Why Skin Comes in Colors
Posted: Wednesday, August 29, 2001The skin is the place where Vitamin D is synthesized using ultraviolet rays to catalyze the reaction. So you need some ultraviolet light to penetrate the skin in order to make Vitamin D. Vitamin D turns out to be critical to your body because it provides the means whereby you absorb calcium from your food in your digestive system. So if you don't have Vitamin D, you can't absorb calcium from your food and you can't build strong bones.
Making the proper skin color turns out to be a balancing act between having enough natural sunscreen to prevent a lot of damage to the contents of the blood system. On the other hand, you have to let in enough ultraviolet light to still permit the formation of Vitamin D in your skin. So people who live in conditions of lower ultraviolet light, away from the tropics and toward the poles, have to have lighter skin than those people who live closer to the tropics or closer to the equator. Those people really have to have darker skin to protect themselves from ultraviolet light.
Those who are sort of in the middle, like inhabitants of most of North America and most of Eurasia, have to have skin that is capable of some level of tanning so that we can protect ourselves from lots of ultraviolet radiation in the late spring and summer. But we can de-pigment ourselves as ultraviolet light becomes less intense in the winter so we can take advantage of the ambient ultraviolet radiation that does exist.
If we look at our earliest Homo sapiens ancestors (about 100 to 150 thousand years ago in eastern Africa), we can reconstruct that those ancestors would have had dark skin to protect themselves from the deleterious effects of ultraviolet light. But those populations began to move out of the tropics and colonize areas that were much less intense in terms of ultraviolet light. As they first moved into the Circum Mediterranean, Western Asia, then onward into Eastern Asia, Europe, Southeast Asia, Australia and so forth, these populations would have to undergo some depigmentation in order for them to be able to synthesize enough Vitamin D in their skin. More
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