That puzzling variant of PLK4, that increases the miscarriage rate, is very widespread, moderately common in almost all population – but it’s rare in Bushmen (frequency of 1 in 38 among the Ju’/hoansi) and Pygmies, enough to you suspect that it wasn’t there at all before the Bantu recently admixed with both groups.
The Bushmen (and probably African Pygmies as well) apparently split off earlier than any other human population, something like 200,000 years ago. Some Bushmen among the Ju’/hoansi, show low or even zero admixture with other groups. How they managed to have so little gene flow with other Africans for such a long time is a mystery to me, but that’s what the stats say. There is more genetic distance between the Bushmen and Bantu than there is between Bantu and Koreans.
This long separation doesn’t necessarily mean that Bushmen ave the most divergent phenotypes (although thinking about it, they probably are, what with steatopygia , the tablier egyptienne, etc) – strength and direction of selection are important, not just time. But all else equal, more time allows greater changes.
This doesn’t mean that the Bushmen are what early homo sap was like – they’ve been evolving too – but we ought to be able to learn quite a bit about changes over the past couple of hundred thousand years by investigating genetic differences between the Bushmen and everybody else. For example, 200 k years ago, our ancestors didn’t have what it takes to out-compete Neanderthals and other archaics on their home grounds, judging by the fact that they didn’t manage it back then. By 40k years ago we could and did – but that isn’t necessarily the case for Bushmen, a separate branch. Although, since Bushmen and Pygmies seem to have picked up a few percent of their genome from some very divergent group of archaic humans, perhaps they too developed the ability to kick archaic ass. But we don’t know if they did it in the same way, and it probably happened in fairly familiar African environments, instead of ice age Eurasia.
By the way, I have a very funny story about Bushman genetics, but there are not enough electrons in this margin.