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human variation- anthro.docx

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University of Toronto Scarborough
Anita Woods

Lecture 11 Human Variation Modern Human Diversity -all humans are one species -why do we see so much physical variation? -mutation- only source of new gene variants -what role do evolutionary forces play in this variation? -natural selection-genes favouring survival become more frequent in population -different environment=different genes favoured -genetic drift-result of small population -few contribute larger share of genes to next generation Eg. Founder effect, social status -gene flow-exchange of genes between populations - = one species over wide geographic area Influences on variation -evolutionary forces= change gene frequencies of genotype -environmental (+cultural) factors influence phenotype - = genetics and environment reflected in phenotype and generate diversity Human Adaptatio -biological plasticity-ability to respond physiologically to changes in environment -acclimation-short term physiologic responses eg. Sweating/shivering -developmental acclimatization-changes occur during growth in response to stress. Eg. Increase in chest size with altitude -adaptation-body size and shape+temperature -bergmann’s and allen’ rules Bergmann’s rule -within same species -heat production function of volume (ie.body mass) -larger=cold climates –smaller=warm climates -heat loss function of surface area -linear body loses heat faster than compact body -colume same, surface area increases; hot climates=linear bodies ; cold climates=compact bodies Allen’s rule -with same species -relationship between protruding parts and temperature ; longer limbs=warm climates; shorter limbs=cold climates -long limbs have more surface area for volume=greater heat loss Nasal sizes and shape -nose-transform ambient air into warm humid air for lungs -long, narrow, projecting nose=dry, cold climates -more surface area to warm and humidify air breathing in, collect moisture breathing out -wider, shorter noses=hot, humid climates -more surface area to dissipate heat and moisture -warm, dry climates-immediate nose form Skin colour -humans lost protection of hair from sunlight -dark skin=decrease risk of skin cancer ; And/Or -protects against folate breakdown (darker) and allows products of vitamin D (lighter) -global variation in UV levels determines balance between 2 factors Selection and Disease -different environments=different infectious diseases -infected resistance to disease=variation between human populations -eg. Sickle cell anemia and malaria resistance Cultural Influences on Variation -modificaction of environment through
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