4. 1AA3-19 - Sex, & Gender to post.pptx

4. 1AA3-19 - Sex, & Gender to post.pptx - ANTH 1AA3 Sex...

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ANTH 1AA3 Sex, Food, and Death Human Variation
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Modern Human Variation Humans are variable They are sexually dimorphic males and females exhibit different physiological traits Humans can also exhibit variation related to adaptations to their ancestral environments & diets (among other things)
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Intro to Human Variation: Skin Colour Very early hominins with hair cover probably had light skin (like chimps) Fur was lost because of: Increased running of early hominins (ca. 1.2 mya)? Increased development of sweat glands for cooling Without hair, skin became darker (melanization) protects against harmful effects of UV radiation
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Modern, Clinal Variation in Skin Colour Indigenous skin colour gradually changes from lighter to darker  in different global regions
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Clinal Variation in Skin Colour The pattern of skin colour changes VERY closely resembles the  pattern of UV radiation on the earth
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Clinal Variation in Skin Colour Indigenous skin colour differences  correlate  with patterns of  ultraviolet radiation. 
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Anthropologists now understand skin colour as an evolutionary adaptive trait related to sun exposure But how/why exactly? Biological anthropologists have worked to understand and explain why our skin colours differ with UV Current thought explains skin colour as related to: 1. Folate 2. Vitamin D
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UV light The Folate Hypothesis (selection for dark skin) Folate (Vitamin B9) is stored in the skin Excessive UV radiation interferes with folic acid synthesis and results in reduced folate levels 8 Risk of folate deficiency in areas of high UV radiation When too much UV light is absorbed, folate is destroyed
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Is folate important? Yes! Link between folate deficiency and neural tube defects in infants (e.g., spina bifida) and fertility Any impact on pregnancy success is an extremely powerful evolutionary selective force ! (if you can’t reproduce, or don’t survive to reproduce, you can’t pass on your genes!) Spina bifida 9
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Folate and Skin Colour 10 Darker skin protects against folate degradation Individuals who are better adapted to high-UV environments (i.e., have dark skin) are the ones that survive to successfully reproduce in those environs The initial populations of early hominins moving out of Africa were likely dark skinned
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The Vitamin D Hypothesis 11 UV light is needed to synthesize Vitamin D (via skin) Vitamin D is essential for uptake of calcium, normal bone growth & mineralization Lack of Vitamin D causes rickets in children
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The Vitamin D Hypothesis Can lead to reduced reproductive fitness , esp. in females, since pelvis may be malformed Any impact on pregnancy success is an extremely powerful selective force 12 Below: ’normal’ pelvis
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Vitamin D Hypothesis Vit. D - synthesized by the skin when exposed to UV radiation If you had darker skin in northern countries, it would inhibit synthesis of Vit. D Lighter skin was ‘selected for’ as humans moved out of Africa and into other, lower UV regions 13
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BUT… Skin colour does not equal race!
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  • Spring '13
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