Powerful evidence for their thesis comes partly from, of all places, a NASA space satellite. Their achievement is strong evidence for the increasingly common belief among scientists that skin color differences are useless for understanding long-term human evolution, including the evolution of races. Jablonski and Chaplin's finding lends powerful support to the belief that over time, peoples' bodies change their skin colors to adjust to different levels of UV light in different regions of Earth.
Light skin absorbs lots of UV, while dark skin absorbs less.
Exposure to too little UV means the skin doesn't generate enough of these chemicals, some of which enhance one's chances of successful reproduction, while too much UV risks destroying those same chemicals or triggering skin cancers. Their research shows that evolution modifies skin colors to adjust to the regional intensity of UV light. It's to boost the chances of reproductive success - breeding lots of healthy kids who live to adulthood and, in turn, have offspring of their own, according to Jablonski, an anthropologist, and Chaplin, a geographic information systems consultant. For a human to remain healthy, his or her skin must absorb enough UV to generate adequate amounts of folate and vitamin D3 to support life processes but not too much. Too much UV would risk triggering skin cancer and chemical destruction of the precious biochemicals.