Nina Jablonski says that differing skin colors are simply our bodies' adaptation to varied climates and levels of UV exposure. Charles Darwin disagreed with this theory, but she explains, that's because he did not have access to NASA. [14:48]
Ooo - I'll have to watch that on Monday when I have access to a decent network. :}
I've known a few Chinese and Koreans who have turned from snow white to really dark in a matter of a week just from being exposed to the sun. I also have a few Irish friends who just burn to a crisp and never seem to get a tan. I've turned a bit darker over the years but the bits that don't get exposed to the sun show my original shade. A few Australian surfers I know have toasted a dark brown and I'm still not used to seeing people walk around with yellow hair, blue eyes, and much darker skin than myself.