I'm pushing very hard on finishing a story right now, so I'm going to make this a short post. This morning I was directed to a really interesting article called "Why Are Europeans White?" The article doesn't have anything to do with races as social groups, but discusses why it is that skin pigmentation is so light in the region surrounding Europe. A hint: it has to do with successful pregnancies, UV light, eating cereals, and ocean currents.
For the details, here's the link.
This is interesting to me in part because it looks at planetary environmental factors, and biological factors, in a human characteristic that clearly has enormous influence on social behavior.