1. Chapter 12 Human Variation and Adaptation Key Terms

2. Dolichocephalic Having a long, narrow head in which the width measures less than 75 percent of the length. Brachycephalic Having a broad head in which the width measures more than 80 percent of the length.

3. Biological determinism The concept that various attributes and behaviors are governed by biological (genetic) factors; the inaccurate association of behavioral attributes with certain biological traits, such as skin color. Eugenics Philosophy of “race improvement” through forced sterilization of members of some groups and encouraged reproduction among others; an overly simplified, often racist, view that is now discredited.

4. Polytypic Referring to species composed of populations that differ with regard to the expression of one or more traits. Cline A gradual change in the frequency of genotypes and phenotypes from one geographical region to another.

5. Population geneticists Geneticists who study the frequencies of alleles, genotypes, and phenotypes in populations. Slash-and-burn agriculture A traditional land-clearing practice whereby trees and vegetation are cut and burned. In many areas, fields are abandoned after a few years and clearing occurs elsewhere.

6. Balanced polymorphism The maintenance of two or more alleles in a population due to the selective advantage of the heterozygote. Lactose intolerance The inability to digest fresh milk products, caused by the discontinued production of lactase, the enzyme that breaks down lactose, or milk sugar.

7. Gene pool The total complement of genes shared by reproductive members of a population. Breeding isolates Populations that are clearly isolated geographically and/or socially from other breeding groups.

8. Endogamy Mating with individuals from the same group. Exogamy Mating pattern whereby individuals obtain mates from groups other than their own.

9. Hardy-Weinberg theory of genetic equilibrium The mathematical relationship expressing— under ideal conditions—the predicted distribution of alleles in populations; the central theorem of population genetics. Population genetics A mathematical and statistical approach used to measure and explain evolutionary change in contemporary populations.

10. Neural tube In early embryonic development, the anatomical structure that develops to form the brain and spinal cord. Spina bifida A condition in which the arch of one or several vertebrae fails to fuse and form a protective barrier around the spinal cord.

11. Vasodilation Expansion of blood vessels, permitting increased blood flow to the skin. Permits warming of the skin and facilitates radiation of warmth as a means of cooling. An involuntary response to warm temperatures, various drugs, and even emotional states (blushing). Vasoconstriction Narrowing of blood vessels, reducing blood flow to the skin. Vasoconstriction is an involuntary response to cold and reduces heat loss at the skin’s surface.

12. Hypoxia Lack of oxygen. Hypoxia can refer to reduced amounts of available oxygen in the atmosphere (due to lowered barometric pressure) or to insufficient amounts of oxygen in the body. Pathogens Substances or microorganisms, such as bacteria, fungi, or viruses, that cause disease.

13. Pandemic An extensive outbreak of disease affecting large numbers of people over a wide area; potentially, a worldwide phenomenon. Vectors Agents that transmit disease from one carrier to another. Mosquitoes are vectors for malaria, just as fleas are vectors for bubonic plague.

14. Endemic Continuously present in a population.