> So human evolution (and survival) matters only until 14-40

Not necessarily. I'd imagine it helps the survival chances of your grandchildren if you're around when they're growing up (though it probably mattered less back when children were raised by communities than in the nuclear families we have nowadays).

Sure, it would have helped homo sapiens even more if more of their children had lived to childbearing ages (if, say, they'd discovered antibiotics a few millenia earlier or evolved more natural immunities). But the infant survival rates back then were enough to ensure the species survived, just like the smaller fraction of the population struck down by skin cancer every year wasn't enough to put evolutionary pressure on us to develop resistance to it or develop sunlight avoidance traits. Evolution doesn't guarantee that every possible beneficial adaptation takes place.

> I'd imagine it helps the survival chances of your grandchildren if you're around when they're growing up

Keeping toddlers from walking off a cliff (and the other things unsupervised toddlers will do to kill themselves) is probably why he said 14-40 and not 14-30.

> human evolution (and survival) matters only until 14-40

I just don't think that's true. I think grand parents being around was important for human survival.

If it wasn't, if all that mattered was having the most kids, then why would women go through menopause? Wouldn't it be better if women continued having children until they die?

I think it makes sense that young people have kids (the sooner the better, faster evolution and less chance of DNA degradation)

Then they should live as long as possible to help raise their grandkids to ensure their genes survive.

> If it wasn't, if all that mattered was having the most kids, then why would women go through menopause? Wouldn't it be better if women continued having children until they die?

Given that the risk of birth defects goes up significantly the older a woman is, menopause is probably evolutionarily advantageous.