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Skin cancer could have driven the evolution of dark skin in humans, a study of people with albinism in modern Africa suggests.
Albinism is an inherited disorder that prevents people from making melanin, a black or brown pigment. Albino people in sub-Saharan Africa almost universally die of skin cancer — and at young ages, according to a paper published Tuesday in the Proceedings of the Royal Society B.
These modern tragedies point to a potential reason early humans evolved to possess dark skin, said Mel Greaves, a cell biologist at the Institute of Cancer Research in the United Kingdom. [Can People Have Blue Skin?]
When human ancestors began hunting and gathering on the open savannah, they lost their body hair, probably because that kept them cooler amid the strenuous exercise of their lifestyle. These early humans probably had pale skin — much like humans' closest living relative, the chimpanzee, which is white under its fur.
Scientists say early Homo sapiens evolved dark skin around 1.2 million to 1.8 million years ago. But why?
"Cancer has been dismissed by effectively all scientists in the past" as the reason for the evolution of dark skin, Greaves told Live Science. "They did so believing that skin cancer cannot be a selective force acting on survival and reproductive success, because in present-day white-skinned people, it is usually benign or impacts too late in life."
Greaves, however, reviewed published cases on albinism in Africa and found that almost all albino individuals developed skin cancer in their 20s due to sun exposure. These early cancers could have been a fact of life for pale humans living in sub-Saharan Africa without the benefit of medical knowledge or sunscreen. As a result, paler people would have died more frequently at younger ages, leaving mostly darker-skinned individuals to pass on their genes.
Lighter skin became prevalent again among humans who moved out of Africa to higher latitudes, where sun-caused skin cancer was less of a factor.