Human Skin Pigmentation

Human skin has many functions, one of which is mediating the effects of sunlight. Pigmentation, (skin color), in humans has evolved under selection pressure from the duration and intensity of sunlight. Ancestral populations near the equator were selected for dark skin, while those living in higher northern latitudes were selected for lighter skin. The distribution of “light” alleles of well-studied genes associated with skin color is non-random. Some of these “light” versions are found in most northern latitude populations; others are more geographically specific.

Most of the known genes (and alleles) for skin color either 1) are part of the biosynthetic pathway for melanin, or 2) regulate melanin biosynthesis. Complicating the story is polygenic inheritance. The expression of the many genes that contribute to skin color results in a continuum of skin color. This continuum becomes more pronounced as populations migrate and interbreed. There are no measureable genetic differences among and between human populations. Thus, the notion of “race” is a societal idea, not a biological trait.