The article said something about the retaining of the ancient DNA in the people of that AO might have been because it gave some protection from disease or some such.
Imo, it was more likely that there was never the intellectual development pressure necessary to deselect the traits given by that DNA.
We’re talking about a people who, when exposed to tech far advanced from their own developed cargo cults in response. The cultures there were also, for the most part, completely unable to raise themselves up out of the stone age without interference from outsiders.
