A fascinating new paper by the University of Utah’s Kristen Hawkes and colleagues supports the “Grandmother Hypothesis,” which says humans evolved their long postreproductive lifespan, shared only by elephants and killer whales, at least in part due to participation of grandmothers in child rearing.
From a summary here:
The theory says that because a few older women among human ancestors began caring for their grandchildren, their daughters could have more children at shorter intervals, and that women ended up evolving long postmenopausal lifespans, unlike female apes who rarely survive past their childbearing years.
I suspect that evolution of the human appetite for protein was likely optimized through selection pressures for having and raising children, possibly including grandchildren, but not for living past age 60. The Grandmother Hypothesis is consistent with this idea, because once grandchildren become independent, grandmothers have almost no further role in enabling survival of their own genes in later generations. Of course, this assumes no significant participation by great-grandparents in raising great-grandchildren.