Chapter 12Human Variation and Adaptation
Key Terms
DolichocephalicHaving a long, narrow head in which thewidth measures less than 75 percent of thelength.
BrachycephalicHaving a broad head in which the widthmeasures more than 80 percent of the length.
Biological determinismThe concept that various attributes andbehaviors are governed by biological(genetic) factors; the inaccurate associationof behavioral attributes with certain biologicaltraits, such as skin color.
EugenicsPhilosophy of “race improvement” throughforced sterilization of members of somegroups and encouraged reproduction amongothers; an overly simplified, often racist, viewthat is now discredited.
PolytypicReferring to species composed of populationsthat differ with regard to the expression ofone or more traits.
ClineA gradual change in the frequency ofgenotypes and phenotypes from onegeographical region to another.
Population geneticistsGeneticists who study the frequencies ofalleles, genotypes, and phenotypes inpopulations.
Slash-and-burn agricultureA traditional land-clearing practice wherebytrees and vegetation are cut and burned. Inmany areas, fields are abandoned after a fewyears and clearing occurs elsewhere.
Balanced polymorphismThe maintenance of two or more alleles in apopulation due to the selective advantage ofthe heterozygote.
Lactose intoleranceThe inability to digest fresh milk products,caused by the discontinued production oflactase, the enzyme that breaks downlactose, or milk sugar.
Gene poolThe total complement of genes shared byreproductive members of a population.
Breeding isolatesPopulations that are clearly isolatedgeographically and/or socially from otherbreeding groups.
EndogamyMating with individuals from the same group.
ExogamyMating pattern whereby individuals obtainmates from groups other than their own.
Hardy-Weinberg theory of geneticequilibriumThe mathematical relationship expressing—under ideal conditions—the predicteddistribution of alleles in populations; thecentral theorem of population genetics.
Population geneticsA mathematical and statistical approach usedto measure and explain evolutionary changein contemporary populations.
Neural tubeIn early embryonic development, theanatomical structure that develops to form thebrain and spinal cord.
Spina bifidaA condition in which the arch of one orseveral vertebrae fails to fuse and form aprotective barrier around the spinal cord.
VasodilationExpansion of blood vessels, permittingincreased blood flow to the skin. Permitswarming of the skin and facilitates radiation ofwarmth as a means of cooling. An involuntaryresponse to warm temperatures, variousdrugs, and even emotional states (blushing).
VasoconstrictionNarrowing of blood vessels, reducing bloodflow to the skin. Vasoconstriction is aninvoluntary response to cold and reducesheat loss at the skin’s surface.
HypoxiaLack of oxygen. Hypoxia can refer to reducedamounts of available oxygen in theatmosphere (due to lowered barometricpressure) or to insufficient amounts of oxygenin the body.
PathogensSubstances or microorganisms, such asbacteria, fungi, or viruses, that cause disease.
PandemicAn extensive outbreak of disease affectinglarge numbers of people over a wide area;potentially, a worldwide phenomenon.
VectorsAgents that transmit disease from one carrierto another. Mosquitoes are vectors formalaria, just as fleas are vectors for bubonicplague.
EndemicContinuously present in a population.