Evolutionary Question

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Why, if white is the coolest “color” (it reflects all the light) and black is the hottest one (it absorbs all the light) — just compare walking in the beach with a white vs. a black t-shirt — , are people in sunny regions darker than those in less sunnier ones?

In other words, why isn’t being white (i.e., more light-reflecting) in sunny regions an evolutionary advantage? Whatever melanin ^WP does (I think it’s supposed to be a sun-blocker), shouldn’t it do it better with the advantage of a more light-reflecting skin?

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elzr Apr 9, 2009

Finally, the answer might be the need for vitamin D.

From the Washington Post’s Scientists Find A DNA Change That Accounts For White Skin:

Unlike most mutations, [whiter skin] quickly overwhelmed its ancestral version, at least in Europe, suggesting it had a real benefit. Many scientists suspect that benefit has to do with vitamin D, made in the body with the help of sunlight and critical to proper bone development.

Sun intensity is great enough in equatorial regions that the vitamin can still be made in dark-skinned people despite the ultraviolet shielding effects of melanin. In the north, where sunlight is less intense and cold weather demands that more clothing be worn, melanin’s ultraviolet shielding became a liability, the thinking goes.

Today that solar requirement is largely irrelevant because many foods are supplemented with vitamin D.

Evolutionary Question

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