Under X amount of human breeding pairs and humans would never recover?

[grude]

I’ve seen this claim thrown around with different numbers of breeding pairs over the years, I think the first claim I saw was an outrageous number like six thousand breeding pairs.

Then after the evidence for actual past population bottlenecks spread through the popular science media the numbers started being adjusted, and I see now the claims on the bottleneck have gone even lower.

http://io9.com/5501565/extinction-events-that-almost-wiped-out-humans

The eruption coincides with a population bottleneck that is often cited as the reason for the relatively low genetic diversity across Homo sapiens sapiens. Research suggests as few as 2,000 humans were left alive by the eruption and its aftereffects.

A recent paper in the Proceedings of the National Academy of Sciences found another population bottleneck much farther back in human history. Genetic studies found that 1.2 million years ago there were as few as 55,000 members of genus Homo, including pre-human hominids like Homo erectus and Homo ergaster. This one is interesting because we don’t have solid evidence of a catastrophic event during that period, so we’re not sure what might have caused the population crash or where to look for more evidence.

Now obviously with something like one breeding pair you’re likely in deep doo doo, but what about 100-200 breeding pairs? Less?

I’m gues what I am asking is how can anyone say with certainty under X number humans would never recover. How can you know without prescience exactly how damaging inbreeding or lack of variety in genetics would be? There are probably many living animals on earth right now(especially domestic animals/pets) with even less genetic variety doing ok.

[TriPolar]

Besides the genetics the survivors have to be located close enough to find each other and reproduce. They would have to all be just the right people also, able to maintain population growth over generations within the environment and without detrimental genes spreading propogating through a small community. 2000 people left after a catastrophic event doesn’t sound like enough unless they were in close proximity.

[septimus]

[QUOTE=West Coast | NOAA Fisheries]

The “50/500” rule of thumb initially advanced by Franklin (1980) and Soule (1980) comes the closest of any to attaining “magic number” status (Wilcox 1986). This rule prescribes a short-term effective population size (N[sub]e[/sub]) of 50 to prevent an unacceptable rate of inbreeding, and a long-term N[sub]e[/sub] of 500 to maintain overall genetic variability. The N[sub]e[/sub]=50 prescription (termed “the basic rule” by Soule 1980) corresponds to an inbreeding rate of 1% per generation, approximately half the maximum rate tolerated by domestic animal breeders (Franklin 1980). The N[sub]e[/sub]=500 prescription is an attempt to balance the rate of gain in genetic variation due to mutation with the rate of loss due to drift, and is based on a genetic study of bristles in Drosophila (Franklin 1980).
[/QUOTE]

I think these numbers are conservative: even smaller populations might be viable, at least in avoiding inbreeding.