C HAPTER 15 Modern Human Biology: Patterns of Variation

H ISTORICAL V IEWS OF H UMAN V ARIATION Biological determinism - cultural and biological variations are inherited in the same way. Eugenics - "race improvement" through forced sterilization of members of some groups and encouraged reproduction among others.

T RADITIONAL C ONCEPT OF R ACE Since the 1960s, race has been used to refer to culturally defined groups. Race is used as a biological term, but has enormous social significance. In any racial group, there will be individuals who fall into the normal range of variation for another group for one or several characteristics.

E XAMPLES OF P HENOTYPIC V ARIATION A MONG A FRICANS (a) San (South African), (b) West African (Bantu), (c) Ethiopian, (d) Ituri (Central African), (e) North African (Tunisia)

R ACISM 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.

I NTELLIGENCE Genetic and environmental factors contribute to intelligence. Innate differences in abilities reflect variation within populations, not differences between groups.

H UMAN P OLYMORPHISMS Characteristics with different phenotypic expressions are called polymorphisms. Geneticists use polymorphisms as a tool to understand evolutionary processes in modern populations.

C LINAL D ISTRIBUTIONS 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. Distribution of the B allele in the indigenous populations of the world.

P ATTERNS OF P OLYMORPHIC V ARIATION Analyzing single traits can be confusing Lewontin’s study People in Sardinia, a large island off the west coast of Italy, differ in allele frequencies at some loci from other European populations.

P OPULATION G ROUPINGS U SED BY L EWONTIN IN P OPULATION G ENETICS S TUDY (1972) Geographic GroupExamples of Populations Included CaucasiansArabs, Armenians, Tristan da Cunhans Black AfricansBantu, San, U.S. blacks AsiansAinu, Chinese, Turks South AsiansAndamanese, Tamils AmerindsAleuts, Navaho, Yanomama OceaniansEaster Islanders, Micronesians AustraliansAll treated as a single group

P OLYMORPHISMS AT THE DNA L EVEL 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.”

P OPULATION G ENETICS 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.

H ARDY -W EINBERG E QUILIBRIUM Hardy-Weinberg Equilibrium The mathematical relationship expressing the predicted distribution of alleles in populations; the central theorem of population genetics. Establishes a set of conditions in a population where no evolution occurs. The hypothetical conditions that such a population would be assumed to meet are as follows: The population is infinitely large to eliminate the possibility of random genetic drift or changes in allele frequencies due to chance. There’s no mutation. There’s no gene flow. Natural selection isn’t operating. Mating is random.

E VOLUTION IN A CTION :M ODERN H UMAN P OPULATIONS Nonrandom mating Endogamy Mating with individuals from the same group. Exogamy Mating pattern whereby individuals obtain mates from groups other than their own. Interbreeding

H UMAN B IOCULTURAL E VOLUTION Humans live in cultural environments that are continually modified by their activities. Evolutionary processes can be understood only within this cultural context. HbS allele

H UMAN B IOCULTURAL E VOLUTION Example: Lactose intolerance In all human populations, infants and young children are able to digest milk. In most mammals, including humans, the gene that codes for lactase production “switches off” in adolescence. The geographical distribution of lactose tolerance is related to a history of cultural dependence on fresh milk products.

F REQUENCIES OF L ACTOSE I NTOLERANCE Population GroupPercent U.S. whites2–19 Finnish48 Swiss12 Swedish4

F REQUENCIES OF L ACTOSE I NTOLERANCE Population GroupPercent U.S. blacks70–77 Ibos99 Bantu90 Fulani22 Thais99 Asian Americans95–100 Native Americans85