Why Did Darker and Lighter Human Skin Colors Evolve?

Humanity’s color gradient probably has little to do with sunburn.

The Crux
By Bridget Alex
Jan 28, 2019 10:00 PMApr 17, 2020 8:42 PM
Africa Tribe Sunset - Shutterstock
Members of the Hamer Tribe walk at sunset in Ethiopia's Omo River valley. Studies show that new skin colors evolved as humans moved north and south from equatorial Africa toward higher latitudes. (Credit: Kimberly Petts/Shutterstock)

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Human skin color reflects an evolutionary balancing act tens of thousands of years in the making. 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. Put simply, dark complexion is advantageous in sunnier places, whereas fair skin fairs better in regions with less sun.

That may seem obvious, considering the suffering that ensues when pale folks visit the beach. But actually, humanity’s color gradient probably has little to do with sunburn, or even skin cancer. Instead, complexion has been shaped by conflicting demands from two essential vitamins: folate and vitamin D. Folate is destroyed by the sun’s ultraviolet (UV) radiation. Whereas the skin kickstarts production of vitamin D after being exposed to those same rays.

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