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stein10_ppt_ch16_rev.ppt© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
Chapter Sixteen
The Biology of Modern Homo sapiens
© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
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Human Adaptability: Adjustments
- Non-genetic changes called adjustments help humans survive in a wide, diverse range of habitats
- Behavioral adjustments are cultural responses to environmental stresses (e.g., housing)
- Acclimatory adjustments are reversible physiological changes to environmental stress (e.g., shivering in an arctic habitat, sweating in a desert habitat)
- Developmental adjustments are variations in the pattern of growth and development due to environmental stress (e.g., chest circumference)
© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
16-*
Human Adaptation
- Adaptations are the result of microevolutionary change.
For example, human
skin color is adaptive
polygenic
(i.e., controlled by
genes at two or more
loci) trait.
Skin color is due
primarily to the
pigment melanin.
© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
Distribution of Skin Color in Indigenous Populations
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Clinal Distributions
- A cline is a gradual change in the frequency of a trait or allele in populations dispersed over geographical space.
- e.g.: skin color of Indigenous people in 1940
- Clinal distributions are thought to reflect natural selection and/or gene flow.
- Consequently, clinal distributions are explained in evolutionary terms.
© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
Skin Color
Gloger’s Rule: within the same species, heavier pigmented
populations to be located toward the equator and lighter
populations to be farther from it.
WHY?
© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
16-*
Human Adaptation
- In general, people living in equatorial regions and their ancestors have darker skin, as a means of protecting the body from harmful UV radiation and to regulate the production of vitamin D.
- In general, people living in Northern latitudes and their ancestors have lighter skin for vitamin D production.
© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
Distribution of Skin Color in Indigenous Populations
© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
Vitamin D Synthesis
© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
Rickets
- Insufficient amounts of vitamin D during childhood result in rickets, a condition that often leads to bowing of the long bones of the legs and deformation of the pelvis.
© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
16-*
The Distribution of Variability
- Scientists have made several generalizations based on the nature of the bodies of various mammals.
- Gloger’s rule: within the same species, there is a tendency for more heavily pigmented populations to be located toward the equator and lightly pigmented populations farther from it.
- Bergmann’s rule: within the same species, the average weight of the members of the population increases and the surface area of the body decreases as the average environmental temperature decreases.
- Allen’s rule: within the same species, the relative size of the protruding parts of the body (e.g., arms and legs) increase as the average environmental temperature increases.
© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
16-*
Growth and Development
- Growth is an increase in the size of an organism.
- Development is a change from an undifferentiated to a highly organized, specialized state.
- Growth and development are influenced by genes and the environment.
© 2011 The McGraw-Hill Companies, Inc. All Rights reserved.
16-*
Puberty
- Adolescent growth spurt, resulting in changes in body composition (e.g., amounts of fat and muscle).
- Changes in the reproductive organs and secondary sexual characteristics are also included.
- The nature and rates of growth and development are controlled by the complex interaction of many factors, including the endocrine glands, nutrition, and heredity.
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16-*
The Secular Trend in Growth and Development
- The secular trend is the tendency over the last hundred or so years for each succeeding generation to mature earlier and grow larger.
- While no one knows for sure what causes this trend, some researchers believe that the following are responsible:
- improvement in nutrition
- better sanitation
- improved health services
- less tedious lifestyles
[Figure 16-17: secular trend]
