Skin Cancer May Have Driven Evolution of Black Skin
WEDNESDAY, Feb. 26, 2014 -- Black skin may have evolved to protect early humans who lived up to 1.8 million years ago from skin cancer, a new study suggests.
The British research team bases their theory on data from today's African pale-skinned albinos -- people with genetic changes that prevent the production of the skin pigment melanin.
The researchers believe that pale-skinned early humans from areas of Africa with the highest exposure to the sun's unhealthy ultraviolet (UV) radiation were under strong evolutionary pressure to develop darker skin to help shield against skin cancer.
"Charles Darwin thought variation in skin color was of no adaptive value and other investigators have dismissed cancer as a selective force in evolution," lead researcher Mel Greaves, director of the Centre for Evolution and Cancer at the Institute of Cancer Research, in London, explained in an institute news release.
"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," Greaves said.
Research suggests the evolution of black skin, rich in the eumelanin pigment that most effectively protects against sun damage, occurred in early humans living between 1.2 and 1.8 million years ago in the East African Savannah.
These early humans likely lost most of their body hair to help stay cooler, revealing pale skin like that of chimpanzees, their closest relatives, Greaves and colleagues suggested.
Although skin cancer is rarely fatal at ages young enough to affect reproduction, the study, published Feb. 25 in the Proceedings of the Royal Society B, revealed that 80 percent of black people with albinism from African equatorial countries such as Tanzania and Nigeria, now die of skin cancer before they reach the age of 30.
There's also an association between albinism and skin cancer among people in Panama and other tropical countries with high, year-round UV exposure, the researchers pointed out in the news release.
The investigators added that increased production of black melanin could have had other health benefits that helped early humans pass on key genes to future generations -- DNA that helped prevent damage to sweat glands or the destruction of folate, a nutrient critical for fetal development.
Looking ahead, the researchers said they plan to continue their investigation of human evolution in order to shed light on why human cancers develop. They will also focus on the development of drug resistance and the genetic diversity within individual tumors.
The U.S. Centers for Disease Control and Prevention provides more information on the risk factors for skin cancer.
Posted: February 2014