When it comes to skin color, the idea that we're really all the same isn't just a utopian dream. A look at skin cancer from an evolutionary perspective suggests that maybe once we were all white; then we were all black; then some of us went back to white.

In a study published in Proceedings of the Royal Society B, Mel Greaves, professor of cell biology at the Institute of Cancer Research in London, looked at some 25 studies of skin cancer in albinos in Africa. Albinos have less melanin, a natural pigment that helps protect the skin against damage from the sun. The more melanin in the body, the darker the skin.

Greaves found that basal cell and squamous