Chapter 12

1. Chapter 12 Human Variation and Adaptation

2. Chapter Outline • Historical Views of Human Variation • The Concept of Race • Racism • Intelligence • Contemporary Interpretations of Human Variation

3. Chapter Outline • Human Biocultural Evolution • Population Genetics • The Adaptive Significance of Human Variation • The Continuing Impact of Infectious Disease

4. Historical Views of Human Variation • Two schools of thought developed to explain diversity: • Monogenists believed that all humans were descended from a original pair of humans. • Polygenists believed that all humans were descended from a number of pairs of humans.

5. Historical Views of Human Variation • Biological determinism - cultural and biological variations are inherited in the same way. • Eugenics - "race improvement" through forced sterilization of members of some groups and encouraged reproduction among others.

6. Traditional Concept of Race • Since the 1600s, race has been used to refer to culturally defined groups. • Race is used as a biological term, but has enormous social significance. • "Racial traits" are not the only phenotypic expressions that contribute to social identity: sex and age are also critically important. • In the 1950's the use of the term "race" was replaced with "ethnicity "

7. Allele FrequenciesWithin and Between Populations • After World War II, the study of human variation shifted to the study of differences in allele frequencies within and between populations. • The application of evolutionary principles to human variation has replaced the view that was based solely on observed phenotype. • Races are no longer viewed as fixed biological entities, composed of individuals fitting a particular type.

8. Groupings Used by Lewontin in Population Genetics Study (1972)

9. Racism • Based on false belief that intellect and cultural factors are inherited with physical characteristics. • Uses culturally defined variables to typify all members of particular populations. • Assumes that one's own group is superior. • A cultural phenomenon found worldwide.

10. Intelligence • Genetic and environmental factors contribute to intelligence. • Many psychologists say IQ scores measure life experience. • Innate differences in abilities reflect variation within populations, not differences between groups. • There is no convincing evidence that populations vary in regard to intelligence.

11. Adaptive Significance of Human Variation • Human variation is the result of adaptations to environmental conditions. • Physiological response to the environment operates at two levels: • Long-term (genetic) evolutionary changes characterize all individuals within a population or species. • Short-term, temporary physiological response is called acclimatization.

12. Pigmentation and Geographical Divisions • Before 1500, skin color in populations followed a geographical distribution, particularly in the Old World. • Populations with the greatest amount of pigmentation are found in the tropics. • Populations with lighter skin color are associated with more northern latitudes.

13. Skin Color Influenced by three substances: • Hemoglobin, when it is carrying oxygen, gives a reddish tinge to the skin. • Carotene,a plant pigment which the body synthesizes into vitamin A, provides a yellowish cast. • Melanin,has the ability to absorb ultraviolet radiation preventing damage to DNA.

14. Thermal Environment • Mammals and birds have evolved complex physiological mechanisms to maintain a constant body temperature. • Humans are found in a wide variety of thermal environments, ranging from 120° F to -60° F.

15. Human Response to Heat • Long-term adaptations to heat evolved in our ancestors: • Sweat Glands • Vasodilation • Bergmann's rule - body size tends to be greater in populations that live in cold environments.

16. Human Response to Cold • Short-term responses to cold: • Metabolic rate and shivering • Narrowing of blood vessels to reduce blood flow from the skin, vasoconstriction. • Increases in metabolic rate to release energy in the form of heat.

17. High Altitude • Multiple factors produce stress on the human body at higher altitudes: • Hypoxia (reduced available oxygen) • Intense solar radiation • Cold • Low humidity • Wind (which amplifies cold stress)

18. Infectious Disease • Caused by invading organisms such as bacteria, viruses, or fungi. • Throughout evolution, disease has exerted selective pressures on human populations. • Disease influences the frequency of certain alleles that affect the immune response.

19. Small Pox • The only disease considered to be eliminated as a result of medical technology • Smallpox has a higher incidence in those with type A or AB than in those type O blood. • The immune systems of individuals with type A antigen may not recognize the small pox antigen as a threat.

20. Impact of Infectious Disease • Before the 20th century, infectious disease was the number one limiting factor to human populations. • Since the 1940s, the use of antibiotics has reduced mortality resulting from infectious disease.

21. Impact of Infectious Disease • In the late 1960s, the surgeon general declared the war against infectious disease won. • Between 1980 and 1992 deaths from infectious disease increased by 58%. • Increases in the prevalence of infectious disease may be due to overuse of antibiotics.

22. Environmental Factors. • Global warming may expand the range of tropical diseases. • The spread of disease is associated with encountering people; this includes crossing borders and penetrating remote areas. • The increasingly large human population leads to overcrowding, unsanitary conditions and the spread of communicable disease.