Modern Human BiologicalVariabilityConcept of RacePhysical Anthropology• Sub-field of Anthropology concerned withhuman biology and evolution• Developed to explain the extent of physicalvariation among living peoplesHuman Biological Variability• POLYGENIST’SSCHOOL• Different groupsencountered were infact different species• “different creations”• variability solved!• MONOGENIST’SSCHOOL• We are all onespecies!• Development of theconcept of RaceBiological Races• Variability seen in typological terms, that is,“types” or “varieties” of humans• Physical anthropology became involved indeveloping the “correct” racial taxonomyClassification of Human Groups• Folk Taxonomies– classification of some class of phenomenonbased on cultural traditions– Do not always correspond to realityFolk Taxonomies of Race inAmerican Culture• European, African, Asian, AmericanIndians, Hispanics• Are these categories reflections of reality?•Yes and No!Folk Taxonomies of Race inAmerican Culture•Yes =• “Social” Race– Social reality– reflected in manyforms of behavior•No =• Biological Race– No biological reality– No racial classificationscheme has any morescientific merit thanany other!– Ethnocentric ideas!Biological Race• A population differing in the FREQUENCYOF CERTAIN ALLELES from otherpopulations within the same species.• Genetic definition• Since we cannot determine allele frequency,we rely on PHENOTYPIC characteristics–ex. Skin colorProblems with RaceClassifications• Typologies are seen as static, stabledivisions in humankind• Based on folk taxonomies of culturaltraditionProblems with RaceClassifications• Gene flow reduces variation!• There are no, and never have been “pure”races• Gene Flow is the Rule!Problems with Race Classifications• White Americans have about• 5% African genes, 3% native American gene• Black Americans have about• 20% European genes; 3% Native American• Native Americans have about• 30% European genes; 5% African genesProblems with RaceClassifications• Early anthropologists were looking forstatistical averages to define racial groups• However, they ignored– 1) Range of Variation– 2) Adaptation to the Environment– Traits existed because of Natural SelectionProblems with RaceClassifications• Physical traits evidenced in people aroundthe world were NOT aspects of a TYPE• But, GENETIC ADAPTATIONS TOENVIRONMENTSSkin color•Dark skin– advantageous near theequator; greater degreeof ultraviolet radiation– Folic Acid• Light-colored skin– advantageous awayfrom the equator– protection from cold– Vitamin D regulation– ex. neanderthalsClinal Distributions• Continuous change in a biological trait ortrait frequency over time and space• expressed in GRADATIONS• Geographic generalizations do exist, but,there are no boundaries between oneexpression of a trait and another• ex. Blood types; skin colorClinal Distributions• Trait boundaries are ARBITRARY• Different traits give different divisions• No concordance• Cluster of traits are useless as criteriaProblems with Racial Types• Biological traits show no concordance– clusters of traits useless• Maybe more variation within defined racialgroups than betweenCULTURE• Major adaptive mechanism• products of cultural ability– social systems, technology, etc.GENETICS• Basis for human biological variability• All populations are constantly evolving– gene frequencies are constantly changing eachgeneration– gene frequency cannot be displayed in anindividualHuman biological races• Are at best a statistical abstraction• Based on frequency of certain allelecharacters observed in small populations• No stable divisions of humans• Human races do not exist in nature as unitsof study in scienceImportant Points to Remember• Biological variation = DYNAMICEVOLUTIONARY PROCESSES• As social barriers are erected & brokendown = gene flow patterns change• Environmental conditions alter = naturalselection shifts• Mutations are always occurringHuman Morphology & Behavior• Are the products of the dynamic interactionbetween•CULTURAL•BIOLOGICAL• ENVIRONMENTAL VARIABLESInterests of Science Today• HOW human biological variation cameabout in terms of the EVOLUTIONARYPROCESSES which created it?• WHAT biological traits arePOLYMORPHIC & determine theirGENETIC BASIS?• WHY is a trait polymorphic?POLYMORHPIC TRAITS• SIMPLE– controlled by a singlegene– # of alleles– stable throughout life– ex. Blood groups• COMPLEX– controlled by manygenes– traits are unstable– environment &developmental changes– ex. Skin color; statureExample of SPT• large set of SPT (30 or more) = bloodgroups•ABO System:– I gene• Ia, Ib, IoABO Blood System• 6 GENOTYPES•AA•AO•BB•BO•AB•OO• 4 PHENOTYPES•type A•type A•type B•type B•type AB•type OSimple Polymorphic Trait• Use blood types in Paternity CasesPunnett SquareSimple Polymorphic Traits• Important = easy to trace• useful for purposes of comparingpopulations at the genetic level!Complex Polymorphic Traits• More difficult to trace– multiple genes are involved– inability to determine exact number– they undergo environmental and developmentalinfluencesCPT• SKIN COLOR = varies with regard toamounts of sunlight striking the earth’ssurface at different latitudes• NOSE FORM = relationship with thetemperature and moisture content of the air• BODY BUILD = selected to some extentaccording to ave. temperature in an areaComplex Polymorphic Traits• Important = in reconstructing theevolutionary history of human polymorphictraitsWhy are there geneticdifferences?• We don’t know completely• All we can do is indicate traits and genesthat seem to be distributed because ofADAPTATIONS to environments• And, carried along by the movements ofpeople and reflect ANCESTRYADAPTATION + ANCESTRY= HUMAN POPULATIONDIFFERENCESBoth processes may act