Yep, the malaria/sickle celled anemia explanation is right on.

On a somewhat related tip, what do you guys think of Darwin's explanation of why different places have different colored folks? He said that it was sexual selection. Basically sexual selection means that in some cultures certain features where more attractive (darker or lighter skin, hair, etc) and over thousands of years those regonal preferences resulted in different colored people. I think that's how it goes anyway, I only read a little bit about it. Not saying that's what happened, just wondering if anyone knows more about that theory or other theories.

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Not every end is a goal. The end of a melody is not its goal; however, if the melody has not reached its end, it would also not have reached its goal. A parable.
--Nietzsche