Early humans may have evolved black skin to protect against a very high risk of dying from ultraviolet light (UV)-induced skin cancer.
Skin cancer has usually been rejected as the most likely selective pressure for the development of black skin because of a belief that it is only rarely fatal at ages young enough to affect reproduction.
But now researchers show evidence that black people with albinism from parts of Africa with the highest UV radiation exposure - and where humans first evolved - almost all die of skin cancer at a young age.
The paper, by professor Mel Greaves at The Institute of Cancer Research, London, cites studies showing that 80 percent or more of people with albinism from African equatorial countries such as Tanzania and Nigeria develop lethal skin cancers before age 30.
Greaves argues that the fact that people with albinism develop cancer at reproductive ages is persuasive evidence that early, pale-skinned humans were under strong evolutionary pressure to develop melanin-rich skin in order to avoid lethal skin cancer.
"While there could have been many benefits of having black skin in Africa, individuals with albinism and no protective benefit from melanin almost all die young from cancer," explained Greaves.
"The clinical data on people with albinism, particularly in Africa, provide a strong argument that lethal cancers may well have played a major role in early human evolution as an important factor in the development of skin rich in dark pigmentation," added Greaves.
Genetic evidence suggests that the evolution of skin rich in the dark pigment eumelanin occurred in early humans between 1.2 and 1.8 million years ago in the East African Savannah.
Most scientists agree the development of black skin occurred in early humans primarily because of the ability of eumelanin to effectively absorb ultraviolet radiation.
The increased black melanin production could have given other benefits that helped individuals to pass on their genes to the next generation - such as preventing damage to sweat glands or the destruction of folate.
Albinism is also linked to skin cancer in indigenous populations of other tropical countries with high, year-round UV exposure such as Panama.
The study was published in Proceedings of the Royal Society B.
