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Modern Human Diversity: Causes, Variation, and Controversies

Explore the causes of physical variability in animals, the usefulness of the biological concept of race in studying human variation, and the validity of studying differences in intelligence between populations. Understand genetic variability and the impact of environment on gene pools, the limitations of race as a classification, factors influencing skin color variation, and the social problem of racism.

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Modern Human Diversity: Causes, Variation, and Controversies

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  1. Chapter 13 Modern Human Diversity

  2. 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?

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

  4. 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.

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

  6. 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.

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

  8. 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.

  9. Distribution of Human Skin Pigmentation Before 1492

  10. 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.

  11. 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.

  12. 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.

  13. Decline in Human Male Sperm Counts

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