Human Biology
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
We are One Species
Humans are numerous, but we're all classified as Homo sapiens. The biological definition of
species is a group of organisms able to interbreed and bear fertile offspring. Any two kinds of
humans are able to reproduce with each other, signifying that all humans belong to the same
species. While it may appear that there are numerous “races,” molecular data show that the DNA
base sequence varies as much between individuals of the same ethnicity as between people of
different ethnicities.
It is generally accepted that the human phenotype is adapted to the climate of a region.
Though dark skin may seem like a defense against the hot rays of the sun, it has been suggested
that it is actually a protection against ultraviolet ray absorption. Dark-skinned individuals living
in southern areas and light-skinned persons living in northern areas absorb the same amount of
radiation. Other features that correlate with skin color, such as hair type and eye color, may also
be side effects of genes that control skin color.
Variations in body shape represent adaptations to temperature. A squat body with short limbs
and nose retains more heat than an elongated body with long limbs and nose. Additionally,
almond-shaped eyes, a flat nose and forehead, and wide cheeks are believed to be adaptations to
the last Ice Age.
While it always has seemed to some that physical differences warrant assigning humans to
different “races,” this rivalry is not borne out by the molecular data noted in this chapter.
Origin of Life
A chemical evolution produced the first cell. In the presence of an outside energy source, such
as ultraviolet radiation, primitive atmospheric gases reacted with one another to produce small
organic molecules.
Subsequently, macromolecules evolved and interacted. The RNA-first hypothesis is supported
by the discovery of RNA enzymes called ribozymes. The protein-first hypothesis is supported by
the observation that amino acids polymerize abiotically when exposed to dry heat. The protocell
must have been a heterotrophic fermenter living on the preformed organic molecules in the
ocean. Eventually, the DNA → RNA → protein self-replicating system evolved, and a proper
cell that could reproduce came into being.
Biological Evolution
Descent from a common ancestor explains the unity of living things—for example, why all
living things have a cellular structure and a common chemistry. Adaptation to different
environments explains the remarkable diversity of living things.
Darwin found much evidence for common descent. The fossil record provides us the history of
life in general and allows us to trace the descent of a particular group. Biogeography shows that
the distribution of organisms on Earth is explainable by assuming organisms evolved in one
locale. The common anatomies and development of a group of organisms adapted to different
environments are explainable by descent from a common ancestor. All organisms have similar
biochemical molecules, supporting the idea of common descent.
Darwin proposed a mechanism for variation called natural selection. Members of a population
exhibit inherited variations and compete with one another for limited resources. The members
with variations that help them survive and reproduce have more offspring, and in this way, the
adaptive traits become prevalent in the next generation. The process of natural selection is
nonteleological.
Humans Are Primates
The classification of humans can be used to trace their ancestry. Humans are primates,
mammals adapted to living in trees. An evolutionary diagram of primates based on anatomical,
molecular, and fossil evidence shows that we share a common ancestor with African apes. This
common ancestor lived about 6 MYA. Researchers are seeking environmental reasons why
humans came down out of trees and walked erect.
Evolution of Australopithecines
The first hominid (humans are in this family) was an australopithecine that lived about 3
MYA. Australopithecines could walk erect, but they had a small brain. This testifies to a mosaic
evolution for humans—that is, not all advanced features evolved at the same time. It is uncertain
which australopithecine is ancestral to early Homo.
Evolution of Humans
H. habilis made tools, but H. erectus was the first fossil to have a brain size of more than 1,000
cc. H. erectus migrated from Africa into Europe and Asia. They used fire and may have been
large-game hunters.
Whereas the multiregional continuity hypothesis suggests that modern humans evolved
separately in Europe, Africa, and Asia, the out-of-Africa hypothesis says that H. sapiens evolved
in Africa but then migrated to Asia and Europe. The Neanderthals were already living in Europe
and Asia before modern humans arrived. The Neanderthals did not have the physical
characteristics of modern humans, but they did have culture. Cro-Magnon is a name often given
to modern humans. Their tools were sophisticated, and they clearly had a culture, as shown by
the art on the walls of caves.
The Nature of Ecosystems
The process of succession from either bare rock or disturbed land results in a climax
community. An ecosystem is a community of organisms plus the physical environment. Every
population in an ecosystem has a habitat and a niche. Some populations are producers and some
are consumers. Producers are autotrophs that produce their own organic food. Consumers are
heterotrophs that consume organic food. Consumers can be herbivores, carnivores, omnivores, or
decomposers.
Energy Flow and Chemical Cycling
Energy flows through an ecosystem. Producers transform solar energy into food for
themselves and all consumers. As herbivores feed on plants (or algae), and carnivores feed on
herbivores, some energy is converted to heat. Feces, urine, and dead bodies become food for
decomposers. Ultimately, all the solar energy that enters an ecosystem is converted to heat, and
thus ecosystems require a continuous supply of solar energy.
Inorganic nutrients are not lost from the biosphere as is energy. They recycle within and
between ecosystems. Decomposers return some proportion of inorganic nutrients to autotrophs,
and other portions are imported or exported between ecosystems in global cycles.
Ecosystems contain food webs, and a diagram of a food web shows how the various organisms
are connected by eating relationships. In a grazing food web, food chains begin with a producer.
In a detrital food web, food chains begin with detritus. The two food webs are joined when the
same consumer is a link in both a grazing and detrital food chain. A trophic level is all the
organisms that feed at a particular link in a food chain. Ecological pyramids show trophic levels
stacked one on top of the other like building blocks. Typically they show that biomass and
energy content decrease from one trophic level to the next. Most pyramids pertain to grazing
food webs and largely ignore the detrital food web portion of an ecosystem.
Global Biogeochemical Cycles
Biogeochemical cycles involve reservoirs, which are parts of ecosystems, such as fossil fuels,
sediments, and rocks, that contain elements available on a limited basis to living things. Pools are
components of ecosystems, such as the atmosphere, soil, and water, that are organized sources of
nutrients for living things.
In the water cycle, evaporation over the ocean is not compensated for by rainfall. Evaporation
from terrestrial ecosystems includes transpiration from plants. Rainfall over land results in
bodies of fresh water plus groundwater, including aquifers. Eventually, all water returns to the
oceans.
In the carbon cycle, organisms contribute as much carbon dioxide to the atmosphere as they
remove. Shells in ocean sediments, organic compounds in living and dead organisms, and fossil
fuels are reservoirs for carbon. Human activities such as burning fossil fuels and trees are adding
carbon dioxide to the atmosphere. Like the panes of a greenhouse, carbon dioxide and other
gases allow the sun’s rays to pass through but obstruct the release of infrared wavelengths. It is
estimated that a buildup of these “greenhouse gases” will lead to global warming. The effects of
global warming could be a rise in sea level and a change in climate patterns, with disastrous
effects.
In the nitrogen cycle, the biotic community, which includes various types of bacteria, keeps
recycling nitrogen back to the producers. Certain bacteria in water, soil, and root nodules can fix
atmospheric nitrogen. Other bacteria return nitrogen to the environment. Human activities
convert atmospheric nitrogen to fertilizer, which is broken down by soil bacteria; humans also
burn fossil fuels. In this way, a large amount of nitrogen oxide (NOx) and sulfur dioxide (SO2) is
added to the ecosystem where it reacts with water vapor to form acids that contribute to acid
deposition. Acid deposition can kill lakes and forests and corrode marble, metal, and stonework.
Nitrogen oxides and hydrocarbons (HC) react to form smog, which contains ozone and PAN
(peroxyacetyl nitrate). These oxidants are harmful to animal and plant life.
In the phosphorus cycle, the biotic community recycles phosphorus back to the producers, and
only limited amounts are made available by the weathering of rocks. Phosphates are mined for
fertilizer production; when phosphates and nitrates enter lakes and ponds, overenrichment
occurs. Many types of wastes enter the rivers and then flow to the oceans, which have now
become degraded from added pollutants.
Conservation Biology and Biodiversity
Conservation biology is the scientific study of biodiversity and its management for sustainable
human welfare. The current unprecedented rate of extinctions has drawn together scientists and
environmentalists in basic and applied fields to address the problem.
Biodiversity is the variety of life on Earth; the exact number of species is not known, but there
are many more insects than other types of organisms. Biodiversity should also be preserved at
the genetic, community (ecosystem), and landscape levels of organization.
Conservationists have found that biodiversity is not evenly distributed in the biosphere, and
therefore saving certain areas may protect more species than saving other areas.
Value of Biodiversity
The direct value of biodiversity is evidenced by the observable services of individual wild
species. Wild species are our best source of new medicines to treat human ills, and they meet
other medical needs as well: for example, the bacterium that causes leprosy grows naturally in
armadillos, and horseshoe crab blood contains a bacteria-fighting substance.
Wild species have agricultural value. Domesticated plants and animals are derived from wild
species, which also serve as a source of genes for the improvement of their phenotypes. Instead
of pesticides, wild species can be used as biological controls, and most flowering plants employ
animal pollinators. Much of our food, especially fish and shellfish, is still caught in the wild.
Hardwood trees from natural forests provide us with lumber for various purposes, including
making furniture.
The indirect services provided by ecosystems are largely unseen but vitally important to our
well-being. These services include the workings of biogeochemical cycles, waste disposal,
provision of fresh water, prevention of soil erosion, and regulation of climate. Many people
enjoy recreating in natural settings. Various studies show that more diverse ecosystems function
better than less diverse systems.
Causes of Extinction
Researchers have identified the major causes of extinction. Habitat loss is the most common
cause, followed by introduction of alien species, pollution, overexploitation, and disease.
(Pollutants often lead to disease, so these were discussed together.) Habitat loss has occurred in
all parts of the biosphere, but concern has now focused on tropical rain forests and coral reefs
where biodiversity is especially high. Alien species have been introduced into foreign
ecosystems due to colonization, horticulture or agriculture, and accidental transport. Among the
many causes of pollution (acid rain, eutrophication, and ozone depletion), global warming is
expected to cause the most instances of extinction. Overexploitation is exemplified by
commercial fishing, which is so efficient that fisheries of the world are collapsing.
Conservation Strategies
To preserve species, it is essential to preserve their habitat. Some emphasize the need to
preserve biodiversity hotspots because of their richness. Often today it is necessary to save
metapopulations due to past habitat fragmentation. In that case, it is best to identify the source
populations and save those rather than the sink populations. A keystone species like the grizzly
bear requires the preservation of a landscape including various types of ecosystems over millions
of acres of territory. Obviously, in the process, many other species may also be preserved.
Conservation today is assisted by two types of computer analysis in particular. A gap analysis
attempts for a fit between biodiversity concentrations and land still available to be preserved. A
population viability analysis indicates the minimum size of a population needed to prevent
extinction from occurring.
Since many ecosystems have been degraded, habitat restoration may be necessary before
sustainable development is possible. Three principles of restoration are: (1) start before sources
of wildlife and seeds are lost; (2) use simple biological processes that mimic natural processes;
and (3) aim for sustainable development so that the environment fulfills the needs of humans.
