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