class_12_2010_for_web

class_12_2010_for_web - 10/4/2010 IB35 Human Biological...

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10/4/2010 1 IB35 Human Biological Variation Class #12 Topics for today: Skin Color: A Tale of Adaptive Compromise Most Scientists Think that Skin Color is an Adaptation to the Environment • The pigment that makes skin dark protects us from the harmful rays of sunlight, like ultraviolet radiation (UVR). What is an Adaptation? • An adaptation is something that enhances the survival and survival and reproductive success of an organism in a particular environment. Human Skin Color is Adaptive • Melanin pigmentation varies by latitude and is related to many latitude-dependent environmental parameters. • Darker skin protects against the deleterious effects of UVR (e.g., sunburn, damage to sweat glands, skin cancer). Human Skin Color is Not Adaptive • Sunburn and skin cancer rarely affect reproductive success. Ski l i b d t f l ti • Skin color is a byproduct of selection on other functions of pigmentation genes. • Skin color has evolved as the result of sexual selection. Skin Pigmentation Regulates the Penetration of UVR into the Skin • It determines both the rate of breakdown of UVR-sensitive compounds and the production of UVR-dependent compounds.
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10/4/2010 2 People with darker skin are found closer to the equator. Skin Color is Measured by Skin Reflectance What Gives Skin its Color? • Melanin • Carotene Carotene • Hemoglobin Melanin in the Skin is an Adaptation to Regulate the Amount of Sunlight Entering the Body Melanin is a Natural Suncreen • Melanin prevents the breakdown of important vitamins while allowing the production of others. Dark Skin was the Original
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class_12_2010_for_web - 10/4/2010 IB35 Human Biological...

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