It's theorized that the body's need for vitamin D synthesized from the sun is what dictated the genetic drift in the DNA that produces melanin. In tropical and many subtropical climes, the need for clothing was minimal and the exposed skin of the body produced much of the vitamin D it needed from sunshine. There was so much sunlight in those climes that man's skin remained dark to reflect the unneeded sunlight.
As man moved into cooler climes, there was less intense sunlight and they adapted to cooler weather by wearing more clothing. Less intense sunlight and more clothing blocked the sunlight reaching the skin. As time went by, those men whose skin was lighter, a beneficial trait since light skin absorbed a greater amount of the sunlight that was available, were more genetically predisposed to produce the amount of vitamin D the body needed, and they endured better than those who didn't. As the generations went by, it was precisely this group that came to dominate the gene pool; thus, passing along this altered gene to their offspring. And the genetic drift towards white skin continued as long as the populations remained separated.
That said, white skin doesn't make white skinned people genetically superior to black or dark skinned people. It's wrong headed to believe that it does.
Originally Posted by I B Hankering
I assume that this trait was found only in neanderthals and homo-sapiens and quite possibly the Dravidians and Cro-magnons.
theres a trait thats absent in Negroids of africa but present in the above races, but I don't remember what that was. I don't think they have the neanderthal gene, I think that is it. the lack of it is pretty curious.