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Humanity

The evolution of light skin from dark skin ultimately has the same end result as every other evolutionary change: to allow human beings to live long enough to reproduce. Although it may seem unlikely that skin pigmentation has anything to do with reproductive fitness, it does. The amount of melanin in an individual’s skin determines the color of their skin. Melanin, a pigment which blocks many wavelengths of sunlight from harming tissue underneath the epidermis and absorbs dangerous UV rays is present in large amounts in dark skin and in smaller amounts in lighter skin.
The fact that melanin blocks sunlight is both advantageous and disadvantageous because human beings also need sunlight to facilitate the production of vitamin D, which is necessary for growth, development and metabolism. In equatorial regions such as Africa, which receive the most direct sunlight, having a large amount of melanin is beneficial in the sense that it grants extra protection from the relatively intense sunlight’s harmful effects, but because of the abundance of sunlight, equatorial populations aren’t harmed by melanin’s adverse effects, which are that it hampers vitamin D production.
Too much melanin did not become a problem until a diaspora occurred where early human populations started migrating away from the equator. These emigrants started facing the adverse effects of having large amounts of melanin because the amount of sunlight in a winter day decreases steadily as one heads away from the equator in either direction. These dark-skinned early humans started encountering problems arising from a deficiency of vitamin D because not enough sunlight could penetrate past their melanin to be used in the production of vitamin D. In such a situation, natural selection would favor individuals whom through mutations in their genetic code, had lesser amounts of melanin (pale skin) because they (not suffering from growth and development problems) would have an advantage in competing for...