Genetic viability
To be genetically viable, i.e having a realistic chance of avoiding the problems of inbreeding, a population of plants or animals requires a certain amount of genetic diversity, and consequently a certain minimum number of members. See effective population size. The minimum is normally somewhere in the region of a hundred unrelated individuals. Where a population has become extremely small in a population bottleneck, due for example to near-extinction of the species, it may have lost its genetic viability, and if numbers recover it will be through inbreeding, possibly leaving an unhealthy population.
