In this TED lecture, Nina Jablonski — scientist, primatologist, and author of Skin: A Natural History — discusses the evolution of human skin color in response to varying levels of UV exposure in different geographical environments.  Inhabitants of equatorial areas, where destructive UVB rays are more prevalent, have evolved darker pigmentation to filter out these harmful rays.  Meanwhile, the skin of residents in northern regions has lightened considerably from its earlier dark pigmentation to allow adequate absorption of Vitamin D, which is especially important during winter months when UVB rays — which also stimulate Vitamin D production — are scarce. 

What’s the evidence for this?  We have found that there is a striking correlation between the levels of UV activity across the globe and the levels of pigmentation in these areas.  In fact, maps of UV activity provided by NASA follow the exact same gradient as maps that show common skin color in different areas.  The relation to natural selection is quite apparent: in areas where UVB rays are plentiful, natural selection would favor darker levels of pigmentation; where they are scarce, selection would favor fairer skin.

As Jablonski puts it, “When people ask you, ‘What is the evidence for evolution?’ you don’t have to think about some exotic examples or fossils; you just have to look at your skin.”