https://en.wikipedia.org/wiki/Population_bottleneck#Toba_cat...
Halley's Comet takes 75 years to make an orbit. It goes out to about 35AU. Let's call that 1 year per AU. That rough, rough number would lead one to conclude that anything from the Oort Cloud moving at a similar speed could take, say, 100,000 years to get here even if it was aimed at us. If triggered by something 70,000 years ago, we'd still have a bunch of millenia to prepare.
Anyway. I'm sure I'm completely wrong.
https://phys.org/news/2016-12-ice-ages-linked-earth-orbitbut...
Too bad that in our dull and rational reality it's just a coincidence.
"A 2005 study from Rutgers University theorized that the pre-1492 native populations of the Americas are the descendants of only 70 individuals who crossed the land bridge between Asia and North America."
https://www.livescience.com/289-north-america-settled-70-peo...