Nina Jablonski and George Chaplin used NASA satellite measurements of UVB intensity to predict the amount of skin pigment that would best block harmful UV rays yet still enable the body to produce sufficient vitamin D in populations around the globe. Their predictions closely match actual skin color variations around the world.

SOURCE: Chaplin, G. (2004) Geographic distribution of environmental factors influencing human skin coloration. Journal of Physical Anthropology 125:292-302. Map updated in 2007.