Class 11 - Skin Color Adaptions

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Integrative Biology
Leslea Hlusko

10/8/13  Yay phenotype variation  Seeing color is beneficial for primates – visual animals o Can see what berries and fruits are good o Care what people look like  Why study skin color o Represents product of 500 million years of evolution  An adaptation is something that enhances the survival and survival and reproductive success of an organism in a particular environment. o Skin color is not adaptive  Skin cancer happens after reproduction  Sun burn don’t matter  Skin color is just a side effect for selection for something else  Sexual selection? o Skin color is adaptive  Melanin varies by latitude  Darker skin protects against UVR (sunburn, damage to sweat glands, skin cancer)  Measure skin color by reflection as opposed to based on a palette o More reflection = lighter skin  Color in skin based on (mainly) melanin, carotene and hemoglobin o Melanin is on the base of the epidermis – acts as a natural sunscreen o Skin: 9lbs, 2 square meters, primarily collagen and water  Monkeys  humans o Less hair, more light o LCA with chimps and humans?  MC1R gene o Melanoctorin 1 Receptor – makes protein that controls hair and skin color  Abundant among Non-Africans and chimps, not in Europe  No variation in Africa  We’ve been hairless for at least 1 million years o Then selection for dark skin  Skin helps with thermoregulation – sweat  Apocrine glands: ear, armpits, groin – milky sweat from hair follicles, bacteria feeds on it and makes it small bad  Eccrine glands: all over, hands, feet, water  Humans = more sweaty than other animals  Babies don’t smell when they sweat – mainly based on eccrine o Sweat works via evaporation – wouldn’t work with fur  Aka: we turned into naked, sweaty, dark animals o Dark because need more melanin to protect against sun o Can decorate yourself more (tattoos and clothes) o People are good at judging  Skin o Positive and negative correlation o Higher UVR, the lower the reflectance, higher melanin, darker  UVR effects o Damage to DNA o Phytoplankton can’t photosynthesize o Damage to cell membranes o Photolysis of bioactive compounds o Catalyzes pre-vitamin D3 synthesis
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