After attending a showing of 2012, this question arose: if a species is being wiped out and one intends to try to “save” it, how many breeding pairs would it take to ensure that it would survive? I initially maintained that one pair MIGHT be enough, figuring that although inbreeding is not ideal it wouldn’t necessarily doom all members of future inbred generations, and/or also that modern techniques of targeted breeding plus perhaps a little scientific dabbling might be enough to save the species. I was told in no uncertain terms, however, that one breeding pair simply isn’t enough, and in some finite number of generations the species would die out (although when pressed, my critic could not say how many generations it would take). If she’s right and I’m wrong, how many breeding pairs WOULD it take to ensure survival of a species? If you need to know which species, btw, for some reason we chose elephants.
One pair is enough. The entire population of the Black Robin of New Zealand’s Chatham Islands, now about 250 individuals, is all descended from a single fertile female.
Even for large animals like elephants, while inbreeding depression can be a problem in small populations, it is not a sentence of death. Whether or not a small population will die out is probabilistic, not deterministic. If the population is managed by humans, planned matings can help minimize inbreeding problems.
Cheetahs have extremely low genetic variability, to the extent that unrelated individuals can accept skin grafts from one another. This is probably due to a prolonged population bottleneck in the past. While this seems to cause some problems such as a low sperm count and motility, until recent population decreases due to human impacts the Cheetah was a very widespread and successful species.