Second, even if "elder people were very important in even the most primitive societies", their role is much much important from evolutionary perspective than the pressures based on reproduction. Which is why most close primates get by with zero roles for post-reproduction grandparents.
Also elder people being "very important in even the most primitive societies" is a cultural and recent in evolutionary timescale phenomenon, first and only secondarily an evolutionary one.
> "lifespan" was low in pre-history, not because no one lived long lives, it was because infant mortality was very high.
They also lived shorter lives to begin with. Even in later historical times (say a couple of millenia or so), people's life expectancy at 15 (meaning, with infant mortality excluded) was much shorter than today.
Nobody said that "no one lived long lives" however. Some did. It's an aggregate limitation, not an absolute one.
I’m open to ideas. The only one I’ve been able to come up with is more second-order: the genetic benefit could come from having your children also pass on your genes, if there was a higher probability of them doing that with their parent alive past reproductive age.
Menopause seems to be a biological adaptation to this - most mammals don't have it, they'll keep on having young until they're totally exhausted, and die not long after. Humans seem to be adapted so that women have a wild-type generation's worth (15-20 years) of useful lifespan post fertility.
This is the lie that needs. to die. Elder people were very important in even the most primitive societies. "lifespan" was low in pre-history, not because no one lived long lives, it was because infant mortality was very high.
https://sc.edu/uofsc/posts/2022/08/conversation-old-age-is-n...