system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:How is it that animals trapped in caves for hundreds of years have enough genetic diversity to survive?
gpt
Genetic diversity isn't really as important as you might think.  Consider: nearly all golden hamsters in captivity are descended from one litter captured in the early 20th century.  Humans care about inbreeding because having one of your kids die from some genetic disease is unacceptable to us.  But for many species, having a dozen, or a hundred, or a thousand offspring with only a couple survivors is the norm.  After a few generations, the lethal alleles are weeded out by natural selection.  

The downside after this happens is that genetic variability is low.  That leaves a population relatively ill-equipped to deal with changing environments and new diseases.  But in isolated caves, neither of those things is very likely.