At one time, natural selection may have favored those who had the darkest variations in skin color to protect against ultraviolet radiation.
Greaves, who studies the role that disease plays in human evolution, believes his study adds credence to the idea that when earlier hominids shed their shaggy hair about two million years ago, exposing their naked, pale skin to the sun on the sun-drenched savanna of Africa, natural selection favored those who had the darkest variations in skin color to protect against the ultraviolet radiation (UVR) that can cause skin cancer.
A scientist argues that 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.
Source: Dark Skin May Have Evolved to Protect Against Skin Cancer
Jablonski and Chaplin predicted the skin colors of indigenous people across the globe based on how much ultraviolet light different areas receive. Graphic by Matt Zang, adapted from the data of N. Jablonski and G. Chaplin
Source: Evolution: Library: The Biology of Skin Color: Black … – PBS