Any mutation that produced lighter skin color would have been a severe disadvantage to those living under the bright African sun. When humans left Africa for less sun intense regions of the world, the selective pressure militating against lighter skin would have relaxed, this probably explains the greater variety of skin color found outside sub-Saharan Africa. Lighter skin colors may have been advantageous at higher latitudes since they allow greater penetration of the sun's UV radiation, a requirement for vitamin D synthesis. This may have led to selection for lightly pigmented skin.Scientists have identified at least 100 genes associated with pigment processing. Though African populations are relatively dark, according to a recent study they possess a greater diversity in skin complexion than all other populations. It is therefore likely that many of the alleles associated with light pigmentation were already present in an ancestral population in Africa prior to their dispersal. When humans migrated out of Africa, the lighter skin causing alleles may have accumulated in one population, either by genetic drift, natural selection, sexual selection or a combination of these effects. Since their effects are additive it is possible light skin could arise over several generations without any new mutations taking place.^{(from wikipidea.com)}

A 2006 study provides evidence that the light skin pigmentation observed in Europeans and East Asians arose independently. They concluded that light pigmentation in Europeans is at least partially due to the effects of positive directional and/or sexual selection