1. From ~1.2 million years ago for at least ~1.35 million years, the ancestors of all people alive were as dark as today’s Africans.
  2. The descendants of any prehistoric people who migrated North from the equator mutated to become light over time because the evolutionary constraint keeping Africans’ skin dark decreased generally the further North a people migrated. This also occurs as a result of selection for light skin due to the need to produce vitamin D by way of the penetration of sunlight into the skin (the exception being if dietary sources of vitamin D are available, as is the case among the Inuit).
  1. The genetic mutations leading to light skin among East Asians are different from those of Europeans, suggesting that, following the migration out of Africa, the two groups became distinct populations that experienced a similar selective pressure due to settlement in northern latitudes.

Thank you, WikiPedia, for finally clearing THAT up.