Radiolab - Blood Buddies

Episode Date: December 28, 2010

In this new short, a tree full of blood-sucking bats lends a startling twist to our understanding of altruism and natural selection.

Wait, you're listening. Okay. All right. You're listening to Radio Lab. Radio Lab. From. W. N. Y. C.

C. See? Yeah. And NPR. I'll say this is Radio Lab, the podcast, and you take it from there. Ready? All right. Okay.

Hey, I'm Chad Abumrod. I'm Robert Crilwich. This is Radio Lab. The podcast. The pod. Let me say it. Okay, sorry. This is Radio Lab.

The podcast. Damn you. You're like, you know what? You know what? actually, this is a sort of appropriate because we want to talk about sharing right now. That's all I was doing that I was trying to share the moment with you in a way. Yeah, unsuccessfully. But so our last hour was all about trying to solve the puzzle of why is there

niceness in a very, very cruel dog-eat dog world? Why would there be any kind of sharing or niceness? And as we asked the scientists in the show, which we called The Good Show, the scientists kept saying over and over again, well, oftentimes what you would call nice behavior is actually disguised selfishness as critters of one kind or other try to push their genes into the future by kind of being nice to particular folks to their sisters, to their cousins, to their mothers and fathers, yes, to those who are from their family which share so many of their genes. Yeah, like according to some, like a real hard-ass biologists could argue, if you're nice to your sister,

you're really just being nice to your own genes in another person's body. We were like, come on. Yeah. Is there another way of thinking about this? And so we met a guy. Yes, my name's Jerry Wilkinson. I'm a professor and chair of the Department of Biology at the University of Maryland College Park. And the story that Jerry told us happened way before he was a chair or anything like that, back when he was a lowly grad student. The first summer of my graduate education, I went to Costa Rica.

This was the summer of 1977. We went all over the country, studied various things, and we had an opportunity to apply for money to stay in Costa Rica and do individual. projects. And Jerry decided what he was going to study were bats. Right. Why bats? Have you always liked bats? I never actually handled a bat before I went to Costa Rica. So I had no prior experience whatsoever. And I was, like anyone, I think, maybe a little bit hesitant, I guess. But he says he just happened to be in this place that had a lot of bats. Because I was on a cattle ranch, otherwise known as the McDonald's of bats.

Yes. Because there's something we haven't told you here. These were... Vampire bats. The common vampire bat which feeds primarily on mammalian blood. And these particular bats, Jerry says, lived down by the river. In hollow trees.

Big ones. Inside, they were like caves. And every night, he says, hundreds of these bats would fly out of their trees kind of like a cloud. And move across the fields, hitting towards... Run cows.

A herd of cows. Basically, they will hop up onto a cow. Sink their teeth. Razor sharp teeth into the cow's neck and start sucking its blood. And in a matter of about a half an hour, they basically swell up like a big tick and fly home to the tree quickly. Then they come back to the trees. Anyhow, what Jerry was really interested in was not so much the cow blood-sucking thing. It was how do the bats behave with each other?

Yeah. So one morning he went down to the river where these bats live, found himself a tree. These trees, some of them, were so big that I could actually lie down inside the tree without bending my knees. We would use binoculars to look up at the top of the cavity, which could be anywhere from 15 feet to 40 feet above the ground. Now, picture this. You're in this tree. It's four stories high. It's dark, it's wet, and up at the top. How many are up there? Maybe 20 would be sort of some of the larger groups. What about poop? Weren't they pooping on you?

Because you write in the direct line. Yes, they do that. And it's sort of like tar when they defecate blood. It's very sticky. But day after day, he would go into these trees, get pooped on, and watch them. Pretty soon he starts to notice that these bats are behaving in ways he didn't expect. They behave quite a bit like primates. Meaning what?

They spend a lot of time grooming each other. Really? 30% of the time in the trees they spend grooming each other. Wow. So there you were looking at these reputedly evil creatures and seeing them kind of snuggle. I mean, were you surprised by this? Oh, yeah. It took me no time at all to become very fond, I guess would be the best way to describe it.

They are very social. They're very interactive. But then Jerry saw one of the bats do something. They went way beyond just being social. You know, it's hard to say. It certainly was not a single observation. But basically here's how it would go. One bat will sort of sidle up to another bat and...

Give her a little hug. They sort of clutch each other with their wings, which are folded up. And then the bat that made the move that came up and gave the hug. You'd see that bat. Try to lick at the mouth of the other bat, the one that's hugging. And if you have a good view, you can actually see the tongue of one bat going into the mouth of the other bat. Like they're giving each other a kiss? Very similar.

Yes. But after seeing this a few times, he realized what really was happening is that the one bat was feeding the other bat. Yes. Giving it a meal. By regurgitating blood. Into the other bat's mouth. And that was a shock. A shock because, well, these weren't moms feeding their babies.

I mean, that we've all seen. And that makes sense. No, these were adult animals. Feeding other adult animals. Food that they could have been eating themselves. Right. Which is weird. That had not been described before.

But then he thought, wait a second, wait a second. I know what's going on here. What? These bats, they're just related. Correct. They're relatives. Close relatives. Yeah.

The idea that was in vogue then and is still in vogue now, and certainly it's actually got much more support now than it did then, is that animals tend to help close relatives and sort of never help anybody who's not a close relative. So he thought that must be it. They're related. But you don't just assume it. You must do.

Test it if you're a scientist. So Jerry said, okay, I'm going to check this out. I'm going to set up a little experiment. Yeah, so he went out and got a bunch of bats that he knew were not related. I think I had two groups of six, total of 12 bats, brought them into my house at the time, went to the slaughterhouse, got a lot of blood, and then every night I would take one of the 12 bats out of the cage and not let it feed while everybody else got access to blood. Which means the sad little bag gets no dinner, but it has to watch the others eat, and it's just getting hungrier and hungrier. Well, how long can a bat go with no blood?

Three days, at most. At most. And then they're dead. So you can imagine that by the time the sun rises, this bat is literally starving. And then at dawn, I would put the female back in who hadn't fed. She will go and beg, please. From other individuals. Please.

And... Weirdly, instead of them saying to her... You're not my sister, bug off. Yeah, according to Jerry, what would happen is that they'd hold still part their lips and... Throw up in her mouth. Thank you. I mean, at that point, I was thrilled

that I had found something that seemed to indicate that it wasn't just all about relatedness. Just to make sure this wasn't a fluke? What I then did over the span of the next two weeks is I continued to take one bat out of the cage every night. And he'd do the whole starver-till-dawn thing

and then put her back in the cage with the others. And she was always fed. by someone from her group and occasionally even by more than one individual from her group. Sometimes one bat would step up and say, okay, here, have something, and then maybe another, sometimes a third. And he thought, I wonder what's going on here. Is this random or is there some kind of system? He just couldn't really tell. So then I just kept track of who fed whom. While I was there, I was staying up all night. I wasn't really doing a lot of analysis of the information. And I was only there for a relatively,

of a short period. I got back up to San Diego. Did the analysis. And discovered that there appeared to be a pattern. If, you know, Sally fed Agnes on the first day and then I later starved Sally, then Agnes fed Sally on the second night. Right. Let's just go through this one more time. If on the first day...

Sally fed Agnes. Then on the second day. Agnes fed Sally invariably, not always, but invariably. What does invariably mean in that? Most of the time? Most of the time, most of the time. So if I'm Agnes, I'm only going to feed Sally under the condition that at some later point in time, she will repay the favor. I feed you, you feed me.

Agnes feeds Sally, Sally feeds Agnes. And if you think about it, this is kind of what friendship is. I mean, we never say that explicitly, but friendship works on these kinds of trades. And Mindy feeds Cindy. Cindy feeds Mindy invariably. In fact, with the bats, Jerry at a certain point, created a kind of matrix that plotted... Who had spent time with whom? The friendships between the individual bats. And that allowed me to actually calculate a number that measured who was the best friends and who were the not such good friends.

Like a friend number? Yes. Oh, this is so eighth grade. And it turns out that number is the best predictor of who will feed whom. It's better than who's related to him. Better? Yes. Although it turned out that they both were important.

Yeah, but I want to write a headline around this. You're saying that buddies beat kin. Yes, yes. Think of what this means. If friends can beat family, first of all, friends are people that you choose. Yeah, I mean, you've stuck with your family, but you can choose your friends. So this is in effect an idea that niceness is really deeply chosen. Yeah.

Well, so what is, in the, in the broad scientific community, does this, does this mean that what you counted and saw open up altogether again the question of who helps who and why? Yes, but now we're talking 1984. That's when this work was published, and that's when the sort of, And I gave talks about it, various places, so it became well-known pretty quickly. And it was a really big deal. In fact, some scientists thought, maybe this is going to revolutionize our whole understanding of niceness in nature and social dynamics and creatures.

Because, you know, maybe this behavior isn't just a bad thing. It's everywhere. And we just haven't been seeing it. We haven't been working hard enough to see it. Like this Jerry guy slept in a tree, got pooped on for weeks on end. Maybe if we pushed ourselves that far, we'd find it. find this all over the place. But no.

Didn't work out that way. There are not many convincing cases that I think people identified in those next few years. So the observation you're making may not be writ large. It just may be writ small? Well, I'm not sure I would describe it exactly that way, but clearly it's how much we can extrapolate. the vampire bat story to other systems is an open question. Well, in your most extrapolative frame of mind, maybe when you're sitting in a bar and your three martinis in, and in your gut, in your drunk gut at that moment, what is your hunch?

Is this a representative case? And we just haven't found it elsewhere, but we will. Or is this a one-off? Oh, I don't think it's unique, but I don't think it's very common. I think it would be quite uncommon. You know, the Empire bats are really pretty special because of this reliance on blood. Here's one story you could tell, says Jerry, way back in the day. Forty thousand or more years in the past. The plains where the bats lived were filled with all of these giant creatures. Big mammals were abundant.

Sabre toothed tigers. Mammoths. Wolves and giant slaws. And all of these things were filled with warm blood, so the bats were very happy. But presumably there was a point in time when, and all of these large mammals disappeared. Really fast. And there are all kinds of theories as to why that happened. The point is...

It must have created a time when vampire bats all of a sudden had a hard time finding prey. At that point, I would think it would have been... behoove a vampire bat to come up with some way to deal with periodic food shortages. And he thinks the strategy they came up with somehow, somehow? What's to share? If they didn't help...

each other, I think you would find vampire bats gone. I mean, we wouldn't see them now. Well, this is interesting. This is a new way to explore the question we've been exploring all this time. Yeah, like, why is there a niceness in the world? Yeah. Now, up to now, we thought, well, mostly niceness is a secret form of selfishness. Selfishness, yeah.

Selfishness dressed up. Get your genes into the future, yeah. Yeah. But this is a different version. This one says, you know, under certain circumstances, for a group of addables, being nice really isn't an option. It's... The only way.

Yeah. Like when the going gets tough, the tough get... Nice. How's that for a bumper sticker? Hi, my name is Kim Yucer, and I'm from Sioux Falls, South Dakota, and I'm a radio lab listener. Radio Lab is supported in part by the Alfred P. Sloan Foundation, enhancing public understanding of science and technology in the modern world. more information about Sloan at www.sloan.org.

Thank you very much. End of message.