Our ancestors eventually lost this fur and gained pigment in their skin. But beneath the body hair, they probably had pale skin based on the fact that our evolutionary cousins, chimpanzees and gorillas, have light skin under dark fur today. That’s because early hominins were almost certainly cloaked in dark fur. Several million years ago, our ancestors’ skin tone would not have been obvious. But for the full story of skin color, we’ve got to go way back to hairier days. That’s the basic explanation, proposed in 2000 and fleshed out since by anthropologist Nina Jablonski and geographer George Chaplin. While the intensity of UV rays is dictated by geography, the amount actually penetrating your skin depends on your degree of pigmentation, or skin color. So humans need a happy medium dosage of sun that satisfies both. Hence, the balancing act: People must protect folate and produce vitamin D. Whereas the skin kickstarts production of vitamin D after being exposed to those same rays. Folate is destroyed by the sun’s ultraviolet (UV) radiation. Instead, complexion has been shaped by conflicting demands from two essential vitamins: folate and vitamin D. But actually, humanity’s color gradient probably has little to do with sunburn, or even skin cancer. That may seem obvious, considering the suffering that ensues when pale folks visit the beach. Put simply, dark complexion is advantageous in sunnier places, whereas fair skin fairs better in regions with less sun. There’s a convincing explanation for why human skin tone varies as a global gradient, with the darkest populations around the equator and the lightest ones near the poles.

Human skin color reflects an evolutionary balancing act tens of thousands of years in the making.

Skin luminophor in humans