An argument can be made that mankind expanded into Africa rather than out. Wouldn't high genetic diversity accompany early settlers and would these earlies not be affected by the various genetic bottlenecks?
Remember, according to Herodotus, the Pygmies lived around Lake Chad in his time. Another interesting thing is the cluster of R1B DNA in central Africa.
Just musing.
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...
| Father left | Father right | |
|---|---|---|
| Mother left | FM | fM |
| Mother right | Fm | fm |