Kristen Hawkes of the University of Utah, after studying the Hadza hunter-gatherers of Tanzania, has proposed that grandmothers must have played an important role in the ascent of Homo sapiens. “Good foraging grannies mean healthy Hadza kids – and that was also true for our ancestors,” she said.
Hawkes argues that when our apeman ancestors were evolving in Africa, females normally died at child-bearing age. Then an occasional female lived a little longer, and would have helped her daughters, when they had their own children, to dig and forage for food. These grandmother-mother pairings thrived, so their genes for longevity would have been passed on. In this way, the slow rise of the senior citizens began.
But now Caspari has extended the idea. It wasn’t granny power on its own that did it; grandfathers played a critical role,
Indeed, as other researchers have pointed out.
Just as grannies helping grand kids to survive will tend to perpetuate the genes for long lives, so will those of the age of grandads covering those of the age of their children do so.
For one of the things about human beings is that we’re long lived for our size. It’s not a hard and fast rule, but there’s a general relationship between size of organism (mammals have a different relationship from reptiles, etc, but the relationship generally holds within each major design of animal) and length of life.
Some have even compared it to the number of heartbeats in a life: shrews have very fast heartbeats, elephants very slow, but not all that different a number of total heartbeats in an average lifespan. And yes, heartbeat is associated with size.
When plotting this relationship humans are way, way, off the trend. Much longer lives than would be expected for our mass/heartbeat.
And one of the reasons is that grandads chased the teenage girls, thus passing on those genes for long lives.
At the extreme it’s been said that every human over 50 owes their existence to dirty old men. An exaggeration, yes, but one with that vital grain of truth in it.