Chapter 12: Human Variation and Adaption
Linnaeus’s taxonomic classification- placed humans into 4 separate categories; assigned
behavioral and intellectual qualities to each group with the least complimentary descriptions to
Johann Friedrich Blumenbach- classified humans into 5 races (white, yellow, red, black, and
brown); emphasized that categories based on skin color were arbitrary and that many traits,
including skin color, weren’t discrete phenomena and that their expression overlapped in groups.
Biological determinism- that concept that phenomena, including various aspects of behavior
(e.g. intelligence, values, morals) are governed by biological (genetic) factors; the inaccurate
association of various behavioral attributes with certain biological traits, such as skin color.
Francis Galton- feared that “civilized society” was being weakened by the failure of natural
selection to eliminate unfit and inferior members; he lectured on the necessity of “race
improvement” aka eugenics.
Eugenics- the philosophy of “race improvement” through the forced sterilization of members of
some groups and increased reproduction among others; an overly simplified, often racist view
that’s now discredited
Polytopic- referring to species composed of populations that differ in the expression of one or
People who have particular combinations of these and other traits have been placed together in
categories associated with specific geographical localities; such categories are called races—
geographically patterned phenotypic variation with a species.
Ethnicity—refers to cultural factors
Before World War II, most studies of human variation focused on visible phenotypic variation
between large, geographically defined populations (descriptive studies); now, the emphasis has
shifted to examining differences in allele frequencies within and between populations as well as
considering the adaptive significance of phenotypic and genotypic variation.
Typological- categories are distinct and based on stereotypes or ideals that comprise a specific
set of traits
Polygenic- characteristics that are influenced by several genes and therefore exhibit a continuous
range of expression
Intelligence- mental capacity; the ability to learn, reason, or comprehend and interpret
information, facts, relationships, and meanings; the capacity to solve problems, whether through
the application of previously acquired knowledge or through insight. 2
Polymorphism- Loci with more than one allele; polymorphisms can be expressed in the
phenotype as the result of genes action (as inABO), or they can exist solely at the DNAlevel
within noncoding regions.
Cline- a gradual change in the frequency of genotypes and phenotypes from one geographical
region to another
In humans, various expressions of many polymorphic traits exhibit a more or less continuous
distribution from one region to another, and most of the traits that have been shown to have a
clinal distribution are Mendelian.
Microsatellites- areas of nucleotide duplication
All human populations outside Africa have much less genetic variation than African populations’
Slash-and-burn agriculture- a traditional land-clearing practice involving the cutting and
burning of trees and vegetation; in many areas, fields are abandoned after a few years and
clearing occurs elsewhere.
Lactase persistence- in adults, the continued production of lactase, the enzyme that breaks down
lactose (milk sugar); this allows adults in some human populations to digest fresh milk products.
The discontinued production of lactase in adults leads to lactose intolerance and the inability to
digest fresh milk.
Population genetics- the study of the frequency of alleles, genotypes, and phenotypes in
populations from a micro-evolutionary perspective
Population- a group of interbreeding individuals that share a common gene pool (the total
complement of genes shared by the reproductive members of a population)
Breeding isolates- populations that are clearly isolated geographically and/or socially from other
Hardy-Weinberg equilibrium- the mathematical relationship expressing, under conditions in
which no evolution is occurring, the predicted distribution of alleles in populations; the central
theorem of population genetics.
Several factors that act to change allele frequencies:
1. New variation (new alleles produced by mutation)
2. Redistribution variation (gene flow or gene drift)
3. Selection of “advantageous” allele combinations that promote reproductive success
Stress- in a physiological context, any factor that acts to disrupt homeostasis; more precisely, the