*(means white skin, like you didn’t know that)
A mutant version of SLC24a5 is the biggest single cause of light skin color in Western Eurasia. It’s very widespread:
The usual explanation is that light skin ( in Western Eurasia), caused by this variant of SLC24A5, a variant of SLC45A2, and a few other loci, is a product of selection for increased vitamin D production in areas with low levels of UV radiation. It also seems likely that being too pale in a sufficiently sunny land would lead to problems, like skin cancer.
But this mutation wasn’t common in the old European hunter-gatherers: it may not have existed at all. While it was probably common in the Sardinian-like farming populations that apparently originated somewhere in the Middle East – Otzi had it.
But you know, this mutation exists at pretty high frequencies in places that seem sunny. Its gene frequency in Moroccans is 90%. In Egypt, 88%. Libya, 92%. Saudis, 95%. 47% in South India. It’s 50% in Sinhalese, right on the equator.
In pure East Asians, and Amerindians, it’s apparently unknown. It’s rare in most of Africa, but you do see it in places like Ethiopia (55%) and peoples like the Masai (27%).
It’s 7% in the San, but we know who to blame for that, don’t we?
So: although this mutation may help with vitamin D in Copenhagen or Tullamore, that can’t be the reason for such high frequencies in North Africa or India.
SLC24a5 does something other than confer more vitamin D: something that resulted in tremendous fitness advantage.