[tjradcliffe]

Grandparents transmit culture to their grandchildren. This is a very good bet as to why humans live such absurdly long lives.

It might even be testable.

I often wonder if the Upper Paleolithic Revolution (https://en.wikipedia.org/wiki/Upper_Paleolithic_Revolution) could be correlated with genetic changes related to longevity. If the genes responsible for our double-lifetimes (we live about twice as long as you'd expect a mammal of our heart rate to survive) were small in number and had mutations that could be traced back to ~50 ky BP it would be strong evidence for this idea.