Kevin Langergraber

Wait, you're listening?

I mean, they would probably say it a little bit more fancy.

So I'm, you know, I would just come.

Well, no, like it is super weird, right?

It is super weird.

And I have a long last name.

Langergraver.

Kevin Langergraver.

I'm an associate professor in the School of Human Evolution and Social Change at Arizona State University.

Yeah.

It shouldn't be, because from the perspective of evolution, right?

Evolution favors traits that get more genes into the next generation.

Well, of course, natural selection isn't everything, right?

Not every trait you look at in an organism has a functional reason.

But, you know, like the vast majority of mammal species, you end up reproducing until you die.

Then it's still super weird that a few don't.

That is the evolutionary puzzle, right?

So let me unpack that.

We're really getting into the weeds here.

Which is a long-term study of this one community of chimpanzees.

It's in southwestern Uganda.

Pretty much smack dab in the middle of Kibale National Park.

So picture like... Huge, huge trees.

Like an open park.

Where every single day... Get up in the morning, have your breakfast and your coffee.

The sun is just starting to come up.

That's when you want to leave and go find the chimps.

Basically, you're writing down what they do.

Like Garbo, for example.

Yeah, exactly, exactly.

This female who now is about 72 years old.

At which point she already had adult kids.

But here's the thing, you know, post reproductive individuals, they exist.

You know, there's always like the occasional old female who doesn't reproduce anymore.

Exactly.

Biological samples.

Yeah.

Urine.

Urine, urine.

Urine collection is actually easier than fecal sample collection because they pee a lot more than they poo.

I don't know about easy, though, because what Kevin has to do is... Is you get a stick from the forest.

Picture a stick that's about three feet long.

And it looks kind of like a Y. Sort of like a weird pitchfork or something.

And then when the chimps are up in a tree, they're peeing down on you and you stick your stick out, you know, away from you so that you don't collect too much pee yourself, you know, on your head and stuff.

And then it fills up that bag.

This is highbrow science.

You're just waiting for Garbo to pee.

And then when she does, you'd better be ready.

We found, you know, smoking gun sort of level of signs that we rarely get.

Because looking at the levels of reproductive hormones.

It was really just easy to tell that.

Yep.

Female chimps.

Garbo and these other old females.

Go through menopause.

Yes.

No.

No, she's not.

Let's think about it.

Monk, Richmond, and Hutcherson.

She had, like, you know, a good relationship with both Hutcherson and Richmond.

What about Monk?

No, Monk, she hated Monk.

Richman and Hutcherson would groom Garbo a lot.

Like zone out in this really zen-like state.

It's like, you know, I'm bald now, but I remember when I used to go to the hairdresser and get my hair cut.

And you could feel like the hairdresser running their hands through your scalp.

I would just zone out and ah.

Also, Richmond and Hutcherson would bring food to Garbo.

You know, share meat with Garbo.

Monkey meat.

Also... If someone would be aggressive to Garbo, often, you know, Richmond and Hutcherson would like chase them off, you know, protecting their mother.

Uh-huh.

No real grandmothering behavior.

No, she's not.

And so because... The grandmother hypothesis doesn't seem to apply to chimps.

The second most prominent hypothesis is called this reproductive conflict hypothesis.

In chimpanzees, males stay in their group for their whole lives.

But the females, the daughters, when they hit puberty, they leave their family group to join another one.

The general reason for this is like avoid inbreeding, right?

Right.

So think of this.

Think of it, you're a female chimp.

You're born in one group.

You disperse to a new group where you want to start having kids.

But as you have your first kid, let's say you have a male.

It eventually grows up.

It has its own kids.

So you're just getting more related to group members.

So now to zoom out a little bit.

Now here's the, why is it called the reproductive conflict hypothesis?

There's a limited amount of resources.

And if you have a kid, that means that some other female in your group can't have a kid.

Reproduction is a zero-sum game.

So there's reproductive conflict between females.

And you're like, who's going to have the next kid?

Me or this young female?

If this young female has this kid, who's she going to have it with?

Well, it could be my son that has the kid with this young female, right?

And my genes could get passed down that way.

So I'm going to get some indirect fitness benefits through this young female's reproduction.

Mm-hmm, mm-hmm.

On the other hand... Can the young female say the same thing about the reproduction of this old female?

No, she shares no genes with the hypothetical offspring of this old female.

So as the evolutionary math would have it— Old females are predicted to sort of cede these reproductive opportunities to the young females and stop reproducing.

But just like the grandmother hypothesis, it's not a perfect fit.

No, I do not.

Oh, what?

I do not.

Wait, so I'm just left hanging?

Right, right.

And left with, I don't know, just the...

The magic and wonder of this world, right?