Early humans evolved black skin to protect against skin cancer, researchers have said, debunking the common myths about skin colour.
Published in the Proceedings of the Royal Society B, researchers at The Institute of Cancer Research in London looked at studies showing rates of skin cancer among people with albinism in Africa.
Genetics show skin that is brown-black in colour developed in early humans between 1.2 and 1.8 million years ago in the East African Savannah. As humans migrated out of Africa and into Europe between 50 - 80,000 years ago, there was less UV exposure, so having paler skin was an advantage as it can absorb more vitamin D.
Previously, the argument about the evolution of black skin as a result of skin cancer was rejected because of the belief the disease was very rarely fatal in people young enough to affect reproduction.
However, study leader Mel Greaves found that 80% or more people with albinism in African equatorial countries like Tanzania and Nigeria develop lethal skin cancer before the age of 30.
She argues that the fact that people with albinism – caused by genetic changes preventing the production of melanin – develop cancer at reproductive age is evidence to suggest early, pale-skinned humans were under evolutionary pressure to develop skin rich in melanin to avoid cancer.
Early humans had lost most of their body hair to cope with heat loss and probably had pale skin containing pheomelanin, characteristic of white skin. In comparison, eumelanin is characteristic of black skin and provides a stronger barrier against the DNA damage that causes skin cancer, providing near complete protection.
Scientists mostly agree that black skin developed because of the ability of eumelanin to absorb ultraviolet radiation, but questions remain over how this might have protected against diseases.
Other benefits of black skin proposed include preventing damage to sweat glands and the destruction of folate, which is involved in foetal development.
Greaves argues that the high rate of people with albinism dying from skin cancer suggests skin cancer is the main driver: "Charles Darwin thought variation in skin colour was of no adaptive value and other investigators have dismissed cancer as a selective force in evolution.
"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."