system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do we know that a species has definitely gone extinct (as opposed to just being extremely rare/elusive)?
gpt
Well, we don't.  In science "definite" answers are few and far between.  However, there isn't much difference between having 10 animals and having 0 animals.  That population of 10 is too small to preserve genetic diversity and survive in the long run.