Since modern humans originated in Africa, then spread all over the world, we know that black or brown is the original skin color. So how did some people turn out to have white skin? It’s all about Vitamin D.
Vitamin D is the vitamin we get from exposure to the sun. A lack of it can make us more susceptible to everything from heart disease to cancer. Lighter skin absorbs more of this valuable vitamin, and lower levels of vitamin D at higher latitudes, where the sun is less intense, are probably what caused the lightening effect of some modern humans.
The further north humans migrated, the more vitamin D they needed and the lighter they got over the generations, due to natural selection. Also, there are some indications that dark skin is more prone to frostbite than white skin, because it emits more heat.
In LiveScience.com, Heather Whipps quotes geneticist Asta Juzeniene as saying, "Highly pigmented people will need to stay in the sun around 6 times longer than light people in order to synthesize the same amount of vitamin D."
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