Oviously the first instances of those genes are cery old. Maybe even neanderthal old. But selection preassure for them to become dominant in a population is due to vitamin d deficieny in pregnancy. And that is mostly an agriculturalist thing. But if there is enough sunligth its not as bad. That explains the north south gradient in skintones as well as darker skinned huntergatherers in high latitudes. And that diserent version of the gene were selectd in west and east asia.
Those are definitely reasonable explanations, especially since you do get more vitamin D w/ less sun the lighter your skin is - and there are trade-offs when you get a lot of sun with light skin. Though the story could also be more complex or even seemingly random (or just historically contingent), also having to do with how people migrated, how big their populations got, etc etc.
Oviously the first instances of those genes are cery old. Maybe even neanderthal old. But selection preassure for them to become dominant in a population is due to vitamin d deficieny in pregnancy. And that is mostly an agriculturalist thing. But if there is enough sunligth its not as bad. That explains the north south gradient in skintones as well as darker skinned huntergatherers in high latitudes. And that diserent version of the gene were selectd in west and east asia.
Those are definitely reasonable explanations, especially since you do get more vitamin D w/ less sun the lighter your skin is - and there are trade-offs when you get a lot of sun with light skin. Though the story could also be more complex or even seemingly random (or just historically contingent), also having to do with how people migrated, how big their populations got, etc etc.