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, researchers said.
A new paper, published in Proceedings of the Royal Society B, cited 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.
Greaves argued that the fact that people with albinism, which is caused by genetic changes that prevent the production of melanin, develop cancer at reproductive ages is indirect but persuasive evidence that early, pale-skinned humans were under strong evolutionary pressure to develop melanin-rich skin in order to avoid lethal skin cancer.
Genetic evidence suggests that the evolution of skin rich in eumelanin, which is brown-black in colour, occurred in early humans between 1.2 and 1.8 million years ago in the East African Savannah.
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Pheomelanin, characteristic of white skin, is red-yellow and packaged into smaller stores under the skin than eumelanin, characteristic of black skin. Eumelanin provides a much more effective barrier against the DNA damage that causes skin cancers, providing almost complete protection.
While most scientists agree the development of black skin occurred in early humans primarily because of the ability of eumelanin to effectively absorb ultraviolet radiation, they have debated exactly how this could have protected early humans against lethal diseases.
"Charles Darwin thought variation in skin colour was of no adaptive value and other investigators have dismissed cancer as a selective force in evolution," said Greaves.
"But 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 - in eumelanin," he said.