1. Human Variation and Adaptation
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 the DNA 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.