Okay guys; This Genetic variation grows from the need for Vitamin D--the more solar you get, the more you produce. So, a person living near the equator gets more sun, and someone living around the Caucasus mountains gets less sun"”to produce more vitamin D, those people who got less sun didn't need the blocking provided by melanin.
So they adapted paler skin. Just as Asians adapted to their environment, and the Africans, Island peoples and Inuit Indians and so on. This is what Humans do. Can you imagine what will happen when we finally start colonizing other worlds?