system
Given the following post, respond as if you're commenting on Reddit:
human
How do scientists know when a species is extinct?
gpt
There's no way to know for sure, but after a certain amount of time without any sightings or other evidence, it's assumed a species is extinct. Every once in a while, there will be a finding of one or more members of a species previously thought extinct, but usually when a population gets to the point of near extinction it's just a matter of time before they're gone.