Chapter 13 Modern Human Diversity

Chapter Outline  What are the causes of physical variability in animals?  Is the biological concept of race useful for studying physical variation in the human species?  Is there validity to studying differences in intelligence from one population to another?

Variation and Evolution  In humans, most behavioral patterns are culturally learned or acquired.  Other characteristics are determined by an interaction between genes and environment.

Genetic Variability  Gene pools of populations contain various alternative alleles.  When the environment changes, their gene pool confers the possibility for physical alteration to meet the change.  When a species is separated into different regions, populations differ in the frequency with which genetic variability is expressed.

Frequency of Alleles for the A, B, and O Blood Groups

The Meaning of Race  Early anthropologists classified Homo sapiens into races based on geographic location, skin color, body size, head shape, and hair texture.  The presence of individuals who did not fit the “type” challenged these racial classifications.  No examples of pure racial types could be found.

East-west Gradient in Frequency of Type B Blood in Europe

Race and Human Variation: Limitations  Race is an arbitrary category, making agreement on any classification impossible.  Humans are complex genetically and often the genetic basis of traits on which racial studies are based is poorly understood.  Race exists as a cultural as well as a biological category.

Distribution of Human Skin Pigmentation Before 1492

Factors in Variation of Skin Color  Transparency or thickness of the skin.  Distribution of blood vessels.  Amount of carotene and melanin in a given area of skin.

Factors in Variation of Skin Color  Exposure to sunlight increases the amount of melanin, darkening the skin.  Selective mating, as well as geographic location, plays a part in skin color distribution.

Racism  Racism is a social problem.  Racist individuals react on the basis of social stereotypes instead of scientific facts.  Behavioral characteristics attributed to race can be explained with culture rather than biology.

Decline in Human Male Sperm Counts