[SophosQ]

Our genetic homogeneity implies that anatomically modern humans arose relatively recently (perhaps 200,000 years ago) and that our population size was quite small at one time (perhaps 10,000 breeding individuals).

-Another strongly supported hypothesis is that there was an near-extinction event that wiped out all but a pocket of human settlements from which we descended. - The diversity in other species that are about as old as ours is significantly far greater than ours suggesting that it is more likely an event like an unusually strong ice-age period that could've worsened our genetic diversity.

[freeflight]

That sounds really interesting, does this hypothesis have a name so I can read up on it a bit more?

[SophosQ]

As for what might explain the near-extinction humanity apparently once experienced, perhaps another kind of catastrophe, such as disease, hit the species. It may also be possible that such a disaster never happened in the first place — genetic research suggests modern humans descend from a single population of a few thousand survivors of a calamity, but another possible explanation is that modern humans descend from a few groups that left Africa at different times.

-It's unlikely that the Toba catastrophe was the root cause of the bottleneck as reasoned in this investigation:

https://www.livescience.com/29130-toba-supervolcano-effects....

- I wonder if the hypothesis of leaving Africa in small groups could be effectively tested.

[dotancohen]

I'm not the OP, but the Toba catastrophe comes to mind. There were a few others.