system
Given the following post, respond as if you're commenting on Reddit:
human
What's the closes humans have ever come to extinction?

What caused it? When was it? Why do we think that's the closest we have been?
gpt
There's a theory that about 70,000 years ago the number of people on the planet may have dropped to about 2,500-4000. 

Lake Toba in Indonesia was formed by a super-volcanic eruption that 
occurred around 70,000 years ago that coincides with a "genetic bottleneck" which can also be used to explain the (generally) low amounts of genetic differences between Homo Sapians today.