Elizabeth Preston

You'll see these groups of kids of mixed ages running around together.

And it's kind of like their school.

They learn from the older kids.

They practice doing adult things.

And so their entertainment is really a way of learning and practicing to be an adult.

That's a really interesting question.

And one of the signature things about our species is menopause.

So this idea that older females stick around when we're not fertile anymore.

And it seems to be not that we turn off our fertility in the middle of life, but rather that we live decades beyond when our fertility naturally stops.

So if you look at, for example, a chimpanzee,

she also peters out in her ability to have kids, maybe around age 50, but that's also around when she would die naturally.

We have kind of tacked on these decades of useful life after the end of our fertile period.

And scientists think that that's because evolutionarily, grandmothers were helping to keep their kids and their grandkids alive and pass on their genes.

And when you look across the animal kingdom, the only other place where you see menopause having evolved is not even in a close human relative at all.

It's in certain whales.

So, for example, in killer whales, they have these matriarchal groups where older female whales who have stopped being fertile lead their families.

They help them find food and they help their children and their grandchildren whales to stay alive.

So this is a really interesting question.

If you look at, again, I've given the example before of the baby gorilla, but this is a good parallel, I think, because it's a great ape.

It's a close relative, but it's very different from a human baby.