Higher genetic diversity doesn't speak to antiquity, it speaks to lifestyles. Once agriculture starts up, the relative population of descendants of the sodbusters will be larger and larger over time, leaving more descendants. Hunter-gatherers have lower birth rates, higher infant mortality, and perhaps even more mix-and-match pairing up. Isolation of small populations means the random survival of different chromosomes. And that doesn't take long, I'm looking at my Penn-Dutch (Deutsch) hitchhiker thumbs right now. :')
A pair of parents have 23 chromosome pairs, each -- that works out to 2^23 squared different combos, only a tiny fraction of which will get expressed. So, for example, if there are three kids, and all five family members get their genetic testing done, it will be found that, at any one chromosome, there are four possible outcomes -- 'left' or 'right' from each parent, FM, Fm, fM, fm. With three kids, it's likely 2:1 at any one position, but could be 3:0. Well, that made sense to me, I'd had to have to draw another one of my world-obscure diagrams...
Kind of what I was getting at. If for sake of argument a bunch of people wandered into Africa and were isolated, say the San and the Hottentots, wouldn't that meet this criteria?
I have noticed in passing that these people share certain unique physical differences with the Adman Islanders, I don't know about DNA, but it seems strange.
t is also interesting to note that the Adman Islanders share the same D Hapologroup with those of the Japanese Islanders and very few others.