This is an area I keep wanting to read more of. I read part of Suzman's (
I think) book on the people of the southern Kalahari and he made the assertion that most of humanity went through a genetic bottleneck, meaning the population fell to super low levels and then expanded from there. So most of Africa and all the world beyond Africa comes from this relatively narrow genetic stock, whereas the people of the southern Kalahari were neither part of the mass die-off nor the disapora beyond Africa (beyond limited mixing, obviously). As a result, this small group of people has more genetic diversity than all the rest of humanity combined.
I wonder how this research touches on that. Unfortunately, I can't seem to get around the paywall for the article on the timeline of human evolution, which might answer that.
