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Evolution Lecture 5

How Does the Earth’s Life Change over Time?

• Biological evolution • The process by which Earth’s life forms change

genetically over time • Helps explain why there is such biodiversity • Widely accepted scientific theory

• Natural selection • Process by which species have evolved from earlier

species

Evolution Explains How Organisms Change over Time

• Fossils • Physical evidence of past organisms • Preserved in rocks or ice

• Fossil record • Entire body of fossil evidence • Uneven and incomplete

• Estimate: fossils found so far represent only 1% of all species that have ever lived

Evolution Depends on Genetic Variability and Natural Selection

• Darwin and Wallace independently proposed the concept of natural selection in 1850s.

• Biological evolution involves changes in a population’s genetic makeup over generations.

• Populations, not individuals, evolve.

Steps of Evolution

1. Genetic variability 2. Natural Selection

Genetic Variability

• First step in evolution: Genetic variability • Occurs through mutations

• Random changes in DNA as cells divide and DNA is copied • Can be the result of exposure to external factors (like

chemicals and radioactivity) • Some mutations can be beneficial, and others can be

harmful • Some can result in heritable traits

Natural Selection

• Natural selection • Environmental conditions favor increased survival and reproduction

of certain individuals in a population • Survival of the fittest

Natural Selection

• Adaptive trait • Improves the ability of an individual organism to survive and

reproduce at a higher rate than other individuals in a population • Given prevailing environmental conditions

Evolution Depends on Genetic Variability and Natural Selection

• Genetic resistance • Example of natural selection at work • Occurs when organisms have genes that can tolerate a chemical designed to kill them • Resistant individuals survive and reproduce

• Some disease-causing bacteria have developed resistance to antibacterial drugs (antibiotics)

Evolution Depends on Genetic Variability and Natural Selection

• Human species adaptations • Strong opposable thumbs • Ability to walk upright • A complex brain

Limits to Adaptation through Natural Selection

• Adaptive genetic traits must precede change in the environmental conditions

• A population’s reproductive capacity • Species that reproduce rapidly and in large numbers are better able

to adapt

Myths about Evolution through Natural Selection

• Five common myths • Survival of the fittest means survival of the strongest. • Evolution explains the origin of life. • Humans evolved from apes or monkeys. • Evolution is part of nature’s grand plan to produce perfectly adapted

species. • Evolution by natural selection is not important because it is just a theory.

How do New Species Arise?

• New species arise in two phases

• Geographic isolation • Reproductive isolation

What Factors Affect Biodiversity?

• New species arise in two phases • Geographic isolation

• Occurs first • Populations migrate or are separated

by some other cause

What Factors Affect Biodiversity?

• Reproductive isolation • Mutation and change by natural

selection occurs in the geographically isolated groups

• Eventually prevents breeding between the groups

What Factors Affect Biodiversity?

Geological Processes Affect Biodiversity

• Tectonic plates affect evolution and the distribution of life on earth

• Locations of continents and oceans have shifted through geologic time

• Species move and adapt to new environments, allowing speciation

• Earthquakes can separate and isolate populations

• Volcanic eruptions can destroy habitats

Artificial Selection and Genetic Engineering

• Artificial selection • Selective breeding (or crossbreeding) • Occurs between genetically similar species • Not a form of speciation • Slow process

• Genetic engineering • Way to speed process of artificial selection • Gene splicing

Extinction

• Extinction • Process in which an entire species ceases to exist

• Endemic species • Found only in one area • Particularly vulnerable to extinction

• Background extinction • Typical low rate of extinction

• 0.0001% of all species per year

Extinction Eliminates Species

• Mass extinction • Significant rise above background level • 20–95% of species are eliminated • Causes unknown but could include:

• Giant volcanic eruptions • Collisions with meteors or asteroids

• Provides opportunity for evolution of new species

• Five mass extinctions

Video

• https://www.youtube.com/watch?v=GShGxrw4xOU&feature=emb_ title