Modern human variation (Ch 12) There's variation in ALL humans - - PowerPoint PPT Presentation

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

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Modern human variation (Ch 12)

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

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How anthropologists understand race

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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

Race is socially constructed

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

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Explaining variation in humans

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• 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

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Explain modern human variation:

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

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Adaptations (functional response to environmental conditions)

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

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• As mass increases, surface

area decreases

• Heat is lost at surface so

increased mass = greater heat retention

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

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Melanin: pigment responsible skin color

• More melanin = darker skin

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Adaptations to Ultraviolet Radiation (UVR)

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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

Adaptations to Ultraviolet Radiation (UVR)

UVR helps make vitamin D Vitamin D deficiencies result in rickets Natural selection for: Lighter skin in northern latitudes

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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

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Adaptations to Ultraviolet Radiation (UVR)

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Stress: heat stroke,... Genetic adaptations Evaporative cooling: sweating cools body down Vasodilation: blood vessels widen increasing blood flow

• Dissipates body heat

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Adaptations to hot temperatures

Stress: hypothermia decreases core body temperature Genetic adaptations

• Shivering

Vasoconstriction: blood vessels narrow decreasing blood flow

• Retain body heat

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Adaptations to cold temperatures

Stress: Hypoxia: oxygen deficiency Acclimatization

• Increase heart/respiration rates
• Increase red blood cell count

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Adaptations to high altitudes

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Stress: Hypoxia: oxygen deficiency Acclimatization

• Increase heart/respiration rates
• Increase red blood cell count

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Developmental acclimatization

• Andeans have larger hearts, chests, red blood cell counts

Adaptations to high altitudes

• 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)

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Adaptations to infectious diseases

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

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Biocultural evolution: biology affects culture and vice versa Biological

• Enzyme that breaks down lactose switches
• ff after weaning
• Adult lactose intolerance in most

populations Cultural

• Dependence on pastoralism increased

frequency of adult lactose tolerance