Blood Buddies

Summary

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Radiolab: "Blood Buddies" (December 28, 2010)

Overview of Episode's Main Theme

In "Blood Buddies," Radiolab hosts Jad Abumrad and Robert Krulwich dive into the mysteries of generosity and niceness in nature, focusing on a remarkable story of vampire bats who share their most precious resource—blood. The episode traces biologist Jerry Wilkinson's groundbreaking research showing that, for vampire bats, sharing food with non-relatives isn't just possible—it's critical to their survival, upending traditional ideas about animal altruism as purely gene-driven.

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Key Discussion Points and Insights

Recap of the Previous Episode & Central Question

• The conversation opens with a playful exchange about sharing (00:00–00:30), setting the stage for an exploration of why animals help each other in what seems to be a cruel, competitive world.
• The hosts review how biologists often see "niceness" as disguised selfishness—helping kin is really helping one's own genes (00:50–01:22).

Introducing Jerry Wilkinson and His Bat Research

• Dr. Jerry Wilkinson, biologist at University of Maryland, shares how he stumbled upon this research during his first summer as a graduate student in Costa Rica in 1977 (01:28–01:50).
• He chose to study vampire bats due to their abundance on local cattle ranches (01:58–02:25).

Vampire Bat Behavior Observed in the Wild

• Wilkinson describes how vampire bats feed at night, returning home engorged on cow’s blood.
• Unexpectedly, he observes:
  • Highly social behaviors: grooming each other for up to 30% of their time (04:17–04:29).
  • Bats "hugging" and "kissing"—one bat licking inside another's mouth (05:01–05:21).
  • Discovery: adult bats regurgitating and feeding blood to other adult bats, not just their young (05:34–05:41).
    • Memorable quote: "And that was a shock...these were adult animals feeding other adult animals food that they could have been eating themselves." — Jerry Wilkinson (05:38)

Testing the Nature of Bat Generosity

• The expectation: such generosity should be limited to close relatives, consistent with gene-centric evolutionary theory (06:04–06:21).
• Wilkinson sets up an experiment with unrelated bats:
  • Starves one bat while others feed, returning the hungry bat to the group to observe whether it's fed by others (06:31–07:16).
  • Results: Non-relatives feed the starving bat by regurgitating blood, contradicting strict kin selection theory (07:24–08:01).
    • Wilkinson's reaction: "At that point, I was thrilled that I had found something that seemed to indicate that it wasn't just all about relatedness..." (07:30)

How Vampire Bat "Friendships" Work

• Further analysis uncovers a pattern: bats reciprocate favors—giving blood to those who have helped them before (08:32–09:15).
  • Jad Abumrad: "If I feed you, you feed me." (09:15)
• Wilkinson formalizes "friend numbers" based on data, finding that social bonds (friendships) are better predictors of sharing than genetic relatedness (09:33–10:01).
  • Memorable quote: "Buddies beat kin." — Robert Krulwich (10:12, echoing Wilkinson's findings)

Implications and Broader Impact

• The research challenged prevailing ideas, suggesting that chosen social bonds, not just genes, are powerful drivers of "niceness."
  • Robert Krulwich: "This is in effect an idea that niceness is really deeply chosen." (10:19)
• Despite early excitement, such reciprocal altruism among unrelated adults has not been widely documented in other species (11:28–12:15).
  • Wilkinson: "I don't think it's unique, but I don't think it's very common...vampire bats are really pretty special because of this reliance on blood." (12:15)

The Evolutionary Why: Survival Demands Sharing

• Theorizing on evolution, Wilkinson explains that mass extinctions of large mammals likely drove bats to develop sharing behaviors as an emergency survival strategy (12:26–13:29).
  • Wilkinson: "If they didn't help each other, I think you would find vampire bats gone." (13:19)
• The episode comes full circle: in extreme circumstances, generosity isn’t an optional virtue but a necessity for survival (13:34–13:57).
  • Jad Abumrad: "When the going gets tough, the tough get nice." (13:57)

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Notable Quotes and Memorable Moments

• On the revolutionary aspect of bat generosity:
  • "I was thrilled that I had found something that seemed to indicate that it wasn't just all about relatedness..." — Jerry Wilkinson (07:30)
• On bats' friendship matrix:
  • "It turns out that number is the best predictor of who will feed whom. It's better than who's related to whom." — Jerry Wilkinson (09:54)
• On the evolutionary necessity of sharing:
  • "If they didn't help each other, I think you would find vampire bats gone." — Jerry Wilkinson (13:19)
• On altruism and survival:
  • "When the going gets tough, the tough get nice." — Jad Abumrad (13:57)

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Timestamps for Key Segments

• Topic Introduction & Relevance of Sharing: 00:29–01:22
• Meet Jerry Wilkinson / Early Bat Research: 01:28–02:25
• Vampire Bat Social Behaviors Observed: 04:17–04:29
• First Observations of Food Sharing: 05:01–05:41
• Testing the Relatedness Hypothesis: 06:31–08:01
• Discovering Reciprocal Sharing / Bat Friendships: 08:13–10:01
• Comparison: Friends vs. Kin: 10:01–10:19
• Why Is This Rare? Evolutionary Perspective: 12:15–13:29
• Summary: Survival Drives Niceness: 13:34–13:57

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Tone and Style

The conversation is lively, playful, and accessible, mixing scientific insight with humorous asides (like joking about being pooped on by bats or comparing the friendship matrix to "eighth grade"). Quotes are direct and capture the speakers' sense of surprise and curiosity. The episode weaves curiosity, wonder, and a bit of skepticism into the heart of scientific discovery.

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Summary Conclusion

This episode of Radiolab uses the surprising generosity of vampire bats to question and expand our understanding of altruism. Wilkinson's research shows that social bonds—like friendships—can shape survival just as strongly as genetic ties. In the world of vampire bats, when life is on the line, sometimes kindness is more than a virtue—it's a strategic lifeline.

Transcript

[A]

Oh, wait, you're listening. Okay. All right. Okay. All right. You're listening to radiolab radio from WNY. See Y&NPR. I'll say this is Radiolab, the podcast, and you take it from there. Ready?

[B]

All right.

[A]

Hey, I'm Jad Abumrad.

[B]

I'm Robert Krilwich.

[A]

This is Radiolab, the podcast, the pod. Let me say it.

[B]

Okay, sorry.

[A]

This is Radiolab, the podcast. Damn you. Sorry.

[B]

Come on.

[A]

No, you know what? Actually this is a sort of appropriate, because we want to talk about sharing right now.

[B]

That's what I was doing is I was trying to share the moment with.

[A]

You in a way, unsuccessfully. 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?

[B]

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 another try to push their genes into the future by being nice to particular folks. To their sisters, to their cousins, to their mothers and fathers, to those who are from their family which share so many of their genes.

[A]

Yeah. Like, according to some, like a real hard ass biologist 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?

[B]

And so we met a guy.

[C]

Yes, my name's Jerry Wilkinson. I'm a professor and chair of the Department of Biology at the University of Maryland, College Park.

[A]

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.

[C]

The first summer of my graduate education, I went to Costa Rica.

[A]

This was the summer of 1977.

[C]

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.

[A]

And Jerry decided what he was going to study were bats.

[C]

Right.

[A]

Now, why bats? Have you always liked bats?

[C]

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.

[A]

But he says he just happened to be in this place that had a.

[C]

Lot of bats because I was on a cattle ranch.

[B]

Otherwise known as the McDonald's of bats.

[A]

Yes.

[B]

Because there's something we haven't told you here.

[C]

These were vampire bats, the common vampire bat, which feeds primarily on mammalian blood.

[B]

And these particular bats, Jerry says, live.

[C]

Down by the river in hollow trees, big ones inside. They were like caves with trees along the rivers.

[A]

And every night, he says, hundreds of.

[B]

These bats would fly out of their trees, kind of like clouds, and move across the fields heading towards run cows.

[A]

A herd of cows.

[C]

Basically. They will hop up onto a cow.

[A]

Sink their teeth, razor sharp teeth into.

[B]

The cow's neck and start sucking its blood.

[C]

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.

[A]

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?

[B]

Yeah.

[A]

So one morning he went down to the river where these bats live, found himself a tree.

[C]

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 15ft to 40ft above the ground.

[A]

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?

[C]

Maybe 20 would be sort of some of the larger groups.

[B]

What about poop? Weren't they pooping on you? Because you write in the direct line?

[C]

Yes, they do that. And it's sort of like tar. When they defecate blood, it's very sticky.

[A]

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.

[C]

They behave quite a bit like primates.

[B]

Meaning what?

[C]

They spend a lot of time grooming each other. Really, 30% of the time in the trees they spend grooming each other.

[A]

So there you were looking at these reputedly evil creatures and seeing them kind of snuggle. I mean, were you surprised by this?

[C]

Oh, yeah. 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.

[B]

But then Jerry saw one of the.

[A]

Bats do something that went way beyond just being social.

[C]

You know, it's hard to say, it certainly was not a single observation.

[A]

But basically, here's how it would go.

[C]

One bat, one bat will sort of sidle up to another bat and give.

[A]

Her a little hug.

[C]

They sort of clutch each other with their wings, which are folded up and.

[B]

Then the bat that made the move that came up and gave the hug, you'd see that bat try to lick.

[C]

At the mouth of the other bat.

[B]

The one that's hugging.

[C]

And if you have a good view, you can actually see the tongue of one bat going into the mouth of.

[A]

The other bat, like they're giving each other a kiss.

[C]

Very similar. Yes.

[B]

But after seeing this a few times, he realized what really was happening is that the one bat was feeding the other bat.

[C]

Yes. Giving it a meal by regurgitating blood.

[A]

Into the other bat's mouth.

[C]

And that was a shock.

[A]

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.

[C]

Right.

[A]

Which is weird.

[C]

That had not been described before.

[A]

But then he thought, wait a minute, open the post. Wait a second. I know what's going on here.

[B]

What?

[A]

These bats, they're just related.

[C]

Correct.

[A]

They're relatives.

[C]

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.

[A]

So he thought that must be it. They're related.

[B]

But you don't just assume it. You must 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.

[A]

Yeah. So he went out and got a bunch of bats that he knew were not related.

[C]

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.

[A]

Which means this sad little bat gets no dinner, but has to watch the others eat.

[B]

And it's just getting hungrier and hungrier.

[A]

Well, how long can a bat go with no blood?

[C]

Three days at most.

[A]

At most.

[C]

And then they're dead.

[A]

So you can imagine that by the time the sun rises, this bat is literally starving.

[C]

And then at dawn, I would put the female back in who hadn't fed. She will go and beg.

[A]

Please.

[C]

From other individuals.

[A]

Please. And weirdly, instead of them saying to.

[B]

Her, you're not my sister.

[A]

Yeah. According to Jerry, what would happen is.

[C]

That they'd hold still, part their lips.

[A]

And throw open her mouth.

[C]

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, but just to make.

[A]

Sure this wasn't a fluke, what I.

[C]

Then did over the span of the next two weeks is I continued to take one bat out of the cage.

[A]

Every night, and he'd do the whole starve her till dawn thing and then put her back in the cage with the others.

[C]

And she was always fed by someone from her group and occasionally even by more than one individual from her group.

[B]

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.

[C]

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 short period. I got back up to San Diego.

[A]

Did the analysis, and discovered that there.

[B]

Appeared to be a pattern.

[C]

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.

[A]

Let's just go through this one more time. If I, on the first day Sally.

[C]

Fed Agnes, then on the second day, Agnes fed Sally. Invariably. Not always, but invariably and much.

[A]

What does invariably mean in that? Most of the time.

[C]

Most of the time. Most of the time.

[B]

So if I'm Agnes, I'm only going.

[C]

To feed Sally under the condition that at some later point in time, she will repay the favor.

[A]

I feed you, you feed me.

[B]

Agnes feeds Sally, Sally feeds Agnes.

[A]

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 traits.

[B]

Mindy feeds Cindy, Cindy feeds Mindy. Invariably.

[A]

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.

[C]

And that allowed me to actually calculate a number that measured who was the best friends and who were the not such good friends.

[A]

Like a friend number.

[C]

Yes.

[B]

Oh, this is so eighth grade.

[C]

And it turns out that number is the best predictor of who will feed whom. It's better than who's related to whom.

[A]

Better.

[C]

Yes. Although it turned out that they both were important.

[B]

Yeah, but I want to write a headline around this. You're saying that buddies beat kin.

[A]

Yes.

[C]

Yes.

[B]

Think of what this means if friends can beat family. First of all, friends Are people that you choose?

[A]

Yeah, I mean, you've stuck with your family, but you can choose your friends.

[B]

So this is in effect an idea that niceness is really deeply chosen. Yeah, well, so what is in the broad scientific community, does this mean that what you counted and saw open up altogether again, the question of who helps who and why?

[C]

Yes, but now we're talking 1984. That's when this work was published and that's when the sort of. I gave talks about it various places. So it became well known pretty quickly.

[A]

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 this all over the place. But no, didn't work out that way.

[C]

There are not many convincing cases that I think people identified in those next few years.

[B]

So the observation you're making may not be writ large, just may be writ small.

[C]

Well, I'm not sure I would describe it exactly that way, but clearly it's. How much we can extrapolate the vampirebat story to other systems is an open question.

[A]

Well, in your most extrapolative frame of mind, maybe when you're sitting in a bar and you're 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?

[C]

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, vampire bats are really pretty special because of this reliance on blood.

[A]

Here's one story you could tell says Jerry.

[C]

Way back in the day, 40,000 or more years in the past, the plains.

[A]

Where the bats lived were filled with all of these giant creatures.

[C]

Big mammals were abundant.

[B]

Saber toothed tigers, mammoths, wolves, and giant sloths.

[A]

And all of these things were filled with warm blood. So the bats were very happy.

[C]

But presumably there was a point in time when all of these large mammals disappeared really fast.

[A]

And there are all kinds of theories as to why that happened.

[C]

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.

[A]

And he thinks the strategy they came up with somehow, somehow was to share.

[C]

If they didn't help each other, I think you would find vampire bats gone. I mean, we wouldn't see them now.

[B]

Well, this is interesting. This is a new way to explore the question we've been exploring all this time.

[A]

Yeah. Like, why is there niceness in the world?

[B]

Yeah. Now, up to now, we've thought, well, mostly niceness is a secret form of selfishness.

[C]

Selfishness?

[A]

Yeah, selfishness.

[B]

Dressing genes into the future. Yeah. But this is a different version. This one says, you know, under certain circumstances, for a group of animals, being nice really isn't an option, it's the only way. Yeah.

[A]

Like, when the going gets tough, the tough get nice. How's that for a bumper sticker?

[D]

Hi, my name is Kim Uecker and I'm from Sioux Falls, South Dakota, and I'm a Radiolab listener. Radiolab is supported in part by the Alfred P. Sloan foundation, enhancing public understanding of science and technology in the modern world. More information about [e-mail]. thank you very much. End of message.