[Nosterrex]

Since dark pigment is a dominate phenotype, your theory doesn’t make much sense. The only way that this could happen is in a community in which female would have to produce a generation in which every offspring had a recessive genotype mutation. Not only that, this generation would have to be completely isolated from sexual intercourse from all other people, including the previous generation. How likely is that?

[allmendream]

Dark pigmentation is, first of all, not a strict dominance/recessive trait and not controlled by a single gene. So you are completely off base right off the bat. A dark skinned and light skinned person do not have a child as dark as the dark skinned parent; the colors blend.

Moreover you have no idea how dominance/recessive traits work, even if it WAS applicable, which it is not.

All it would take for a black population to become a white population due to vitamin D deficiency from living in a northern climate is a slight reproductive advantage towards being even slightly lighter skinned for a couple thousand years.

A lighter skinned individual in northern climates where vitamin D could be a problem DO have a reproductive advantage over those darker skinned individual who would develop rickets from vitamin D deficiency.