Originally Posted by factotum
There's evidence that the entire human species was reduced to a few thousand individuals (some studies say as low as 40 breeding pairs) due to a supervolcano eruption 70,000 years ago--we came within a hair's breadth of extinction.
This is the Lake Toba super-eruption from 74 kya.

Also, do you have citations for the studies claiming 40 breeding pairs?

Originally Posted by Rockphed
70,000 years ago there were humans across eurasia, just not Homo [s]apiens.
Might be more accurate to say “not just Homo sapiens,” since a recent discovery from Fuyan Cave in southern China shows the presence of Homo sapiens from at least 80 kya, if not earlier.

Originally Posted by Rockphed
Species of our genus seem to be at least somewhat cross fertile since most people outside of Africa have some neanderthal DNA.
More to the point, there’s at least one known Neanderthal/Denisovan hybrid, and there’s some conjecture that interbreeding with Denisovans gave proto-Tibetans (or a prior population) genes allowing for better adaptation to high-altitude living.