Chapter 15 & 16

1. Chapter 15 & 16 Human Variation and Adaptation

2. Chapter Outline • Historical Views of Human Variation • The Concept of Race • Racism & Intelligence • Contemporary Interpretations of Human Variation • Human Biocultural Evolution • Population Genetics • The Adaptive Significance of Human Variation • The Continuing Impact of Infectious Disease

3. Historical Views of Human Variation • Early human classification • Biological determinism • Eugenics - "race improvement“ • “Three generations of imbeciles is enough” • The Mismeasure of Man by S.J. Gould

4. Traditional Concept of Race • Since the 1600s, race = ethnicity. • Biological fallacy but social reality. • The characteristics that define races are influenced by several genes, and exhibit a continuous range of expression. • More genetic variation within one race than other “different” races.

5. 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.

6. 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.

7. Human Polymorphisms • Polymorphisms • Genetic trait with 2+ alleles. • Used as a tool to understand evolutionary processes. • Clinal Distributions • A cline is a gradual change in the frequency of a trait or allele in populations dispersed over geographical space. • Example: The distribution of the A and B alleles in the Old World.

8. Distribution of the B Allele in Indigenous Populations

9. Polymorphisms at theDNA Level • Molecular biologists have recently uncovered DNA variability in various regions of the genome. • Scattered through the human genome are microsatellites, sites where DNA segments are repeated. • Each person has a unique arrangement that defines their distinctive “DNA fingerprint.”

10. Evolutionary Interactions Affecting the Frequency of the Sickle-cell Allele

11. Population Genetics • The study of the frequency of alleles, genotypes, and phenotypes in populations from a microevolutionary perspective. • A gene pool is the total complement of genes shared by the reproductive members of a population. • Breeding isolates are populations that are isolated geographically and/or socially from other breeding groups.

12. Hardy-Weinberg Equilibrium • The mathematical relationship expressing the predicted distribution of alleles in populations; the central theorem of population genetics. • Provides a tool to establish whether allele frequencies in a human population are changing (see appendix C, p.391). • Formula= p2 + 2pq + q2 p= frequency of dominant allele q= frequency of recessive allele

13. Factors that Act to Change Allele Frequencies • New variation (i.e., mutation) • Redistributed variation (i.e., gene flow or genetic drift) • Selection of “advantageous” allele combinations that promote reproductive success (i.e., natural selection, sexual selection)

14. 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 evolutionary changes characterize all individuals within a population or species. • Short-term, temporary physiological response is called acclimatization.

15. UV Light and Vitamin D Synthesis

16. 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.

17. 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.

18. 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. • Human Response to Heat • Long-term adaptations to heat evolved in our ancestors: • Sweat Glands • Vasodilation

19. 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.

20. 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)

21. 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.

22. Impact of Infectious Disease • Before the 20th century, infectious disease #1 limiting factor. • Since the 1940s,antibiotics reduced mortality rates. • In the late 1960s,war against infectious disease won. • Between 1980 and 1992 deaths from infectious disease increased by 58%. • Increases may be due to overuse of antibiotics.