Modern human variation (Ch 12) There's variation in ALL humans Polytypic species: composed of populations that differ in the expression of one or more traits -Geographically variable pattern among human populations 1
How anthropologists understand race In sum Race is not biologically real -Arbitrary and subjective Race is useless for studying human variation -More variation within populations than between populations -Traits used to classify race exhibit continuous variation Race is socially constructed -Historical, sociocultural factors influence how humans construct racial groups 2
Race is socially constructed Ex: President Obama: first Black president Socially constructed identity: Obama identifies as Black Biological ancestry: European mother ancestry and African father -The Black identity emphasizes African ancestry in the US while Black identity in Brazil skin physical appearance is emphasized -Sociocultural and historical factors explain the differences between these racial categories 3
Explaining variation in humans Modern human variation is due to adaptations to maintain homeostasis Homeostasis: when an individual has a stable internal environment Stress: environmental factors disrupt homeostasis Many variations reflect our African origins 4
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Explain modern human variation: -Our body's struggle to maintain homeostasis (balance of bodily functions, organs, tissues, cells) - Adaptations evolved as mechanisms to maintain homeostasis when under stress -Different environmental conditions cause stress 6
Adaptations (functional response to environmental conditions) Genetic adaptations: evolutionary changes characterizing all members of a species -Irreversible -Transmitted genetically Acclimatization adaptations: rapid adjustments to differing environmental conditions -Reversible -Affected by duration and exposure to environmental conditions Developmental acclimatization when exposed to environmental conditions during growth and development -Irreversible -Not transmitted genetically Cultural adaptations: human practices used in response to environmental conditions 7
Bergmann's Rule: change in body mass-to-surface area differ with thermal environment Allen's Rule: change in appendage shape differ with thermal environment -As mass increases, surface area decreases -Heat is lost at surface so increased mass = greater heat retention 8
Hotter climates: gracile bodies with longer appendages Ex: Populations in sub-Saharan Africa Colder climates: stockier bodies with short appendages Ex: Populations in the Arctic 9
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Adaptations to Ultraviolet Radiation (UVR) Melanin: pigment responsible skin color -More melanin = darker skin 11
Adaptations to Ultraviolet Radiation (UVR) Too little UVR in northern latitudes: -Lighter skin takes advantage of UVR positive effects Too much UVR at equator -Darker skin protects against UVR negative effects 12
Adaptations to Ultraviolet Radiation (UVR) UVR helps make vitamin D Vitamin D deficiencies result in rickets Natural selection for: Lighter skin in northern latitudes 13
Adaptations to Ultraviolet Radiation (UVR) UVR depletes folic acid Folate deficiencies increase risk of having children with birth defects like spina bifida Natural selection for: darker skin at equator 14
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Adaptations to hot temperatures Stress: heat stroke,... Genetic adaptations Evaporative cooling: sweating cools body down Vaso dilation : blood vessels widen increasing blood flow -Dissipates body heat 16
Adaptations to cold temperatures Stress: hypothermia decreases core body temperature Genetic adaptations -Shivering Vaso constriction : blood vessels narrow decreasing blood flow -Retain body heat 17
Adaptations to high altitudes Stress: Hypoxia: oxygen deficiency Acclimatization -Increase heart/respiration rates -Increase red blood cell count 18
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Adaptations to high altitudes Stress: Hypoxia: oxygen deficiency Acclimatization -Increase heart/respiration rates -Increase red blood cell count Developmental acclimatization -Andeans have larger hearts, chests, red blood cell counts 20
Adaptations to infectious diseases -Pathological conditions caused by microorganisms -Less harmful for hunter-gathers Sedentism: infectious diseases thrive in stationary, large communities -Unsanitary conditions Domestication: increased reliance on animals = increased exposure to zoonotic diseases (tuberculosis, influenza) 21
Adaptations to infectious diseases Vector: agents transmitting disease from carrier to carrier Ex: Bubonic plague = bacterium transmitted from fleas to humans Pandemic: outbreaks affecting large #s of people over a wide area Ex: 1918 influenza outbreak killed 20-100 million people Endemic: diseases that are continuously present in a population Ex: Milder forms of influenza in the US 22
Biocultural evolution: biology affects culture and vice versa Biological -Enzyme that breaks down lactose switches off after weaning - Adult lactose in tolerance in most populations Cultural -Dependence on pastoralism increased frequency of adult lactose tolerance
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