Obvously many people think that the human line began with only a very few.

So far as I've seen, there's little to indicate a near-extinction episode after the line became identifiably "human," although it might be that I just didn't notice the headlines when it was reported. Another recent thread discussed the MRCE/MRCA theories, which have been misinterpreted by quite a number of people as meaning that the population dwindled to very small numbers at some recent point. That is NOT a correct understanding of the MRCE/MRCA arguments, but you really have to do the math to understand why, and how, it's wrong.

One of the narrowest genetic lines appears, according to some reports, to be among orangutans, and is attributed to their near extinction sometime after "being orang" was an established thing, by the HIV virus (quite recently on evolutionaly time scales). The survivors were only those resistant to the virus, and orangs remain nearly unique as one of the only known animals that (a) does not harbor the virus and is unlikely to pass it around and (b) is almost completely immune to it and can't be infected with it.

Other critters that seem immune (or at least tolerant) normally are "carriers," and/or "hosts" and have "learned" to live with the infection, rather than by developing an immunity that rids them of it.

Some estimates have placed the low point of the orang population at as few as 20 to 40 individuals who survived from a much larger earlier population. The most believable reports I've seen place the time of this event less than about 16 million years back, and a few "plausible" estimates would have it much more recent.

The orang's narrow genetic base is fairly often cited in passing, but most of the good reports were quite a while back, and I'm sorry but I don't have citations for any. Most of what I think I remember of the more rigorous discussions dates back to when early HIV researchers were looking for host animals for lab use, and had difficulty figuring out why testing on orangs didn't work. (1960 - 1980 era perhaps?) [It would have been convenient for the victims among us if orangs could be infected, as they're genetically very close to humans; but it's obvously fortunate for the orangs that they're immune.]

John