Kleptotherms

Summary

Radiolab — "Kleptotherms"

Date: February 6, 2026
Hosts: Lulu Miller & Latif Nasser
Theme: The deep ties between warmth—physical, emotional, and social—and our lives, exploring how creatures (including humans) "steal" heat, what warmth means for those on the edges, and why our most trusted number in health may be more myth than fact.

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Episode Overview

This episode of Radiolab takes listeners on an imaginative and investigative journey into the notion of warmth—how organisms seek, share, and sometimes "steal" it in surprising ways. Starting with the natural phenomenon of kleptothermy (the act of stealing heat from others), the show unspools stories that wander from the animal kingdom to human experiences of mental illness, social isolation, and the way body temperature became a cultural touchstone. Throughout, Miller, Nasser, and their guests probe at where the line between biological need and social signal begins to blur, leaving listeners with a new sense of how temperature is woven through both body and mind.

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1. Kleptothermy: The Art of Stealing Heat

[01:13–06:30]

Key Points

• Lulu Miller invites listeners on a whimsical “storybook” journey, introducing the concept of kleptothermy—obtaining heat from another creature ("engaging in heat theft").
• Hans Isermann, a social scientist at University Grenoble Alps, shares examples from the animal kingdom:
  • The blue and black amphibious sea snake of New Caledonia sneaks into seabird burrows to "hug" birds, absorbing their heat without eating them.
    • “[The snakes] take advantage of the mass body heat in warming their own bodies.” (Hans Isermann, 03:43)
  • Male garter snakes pretend to be female to stimulate mating attempts from other males, gaining warmth through friction.
  • Dwarf caimans lie on termite nests to absorb collective bug heat.
• Humans also "steal" heat through huddling/cuddling—an act that, in scientific terms, is at least partially theft.
• Biologists see this as part of the “economy of action”—using less energy by sharing warmth is more efficient than creating it on one’s own.
  • “Getting our warmth from another creature is super efficient. It can decrease the cost of thermoregulation by up to about 60 or 70%.” (Hans Isermann, 05:29)
• Our sensations of warmth are deeply social and communal, a bond that shaped how we survived winters.

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2. Redundant Clothing: Schizophrenia, Warmth, and Isolation

[06:51–22:22]

Key Points

• The story of John, a man from Connecticut, tracks his struggles with weight, mental illness, and experiences of cold:
  • As John’s mental illness (schizoaffective disorder, later paranoid schizophrenia) becomes more severe, he begins wearing excessive layers—even in summer.
    • “I think it's a way of shielding myself from the world...I was just doing what felt natural.” (John, 13:56)
  • He observes social judgment—others fear or shun him when they see his unusual attire.
• Multiple psychiatrists (in India, Australia, the US) notice the same "redundant clothing" behavior in patients with schizophrenia.
  • Dr. Tathagata Mahintamani's studies find that patients wearing layers have lower T3 and T4 thyroid hormone levels, markers linked to temperature regulation:
    • “With cold intolerance, like, you just get cold quicker.” (Dr. Mahintamani, 15:08)
  • Suggests that the need for layers may be due to actual physiological coldness—not just confusion, erraticism, or lack of motivation.
• Non-treatment, or "going it alone," in schizophrenia appears correlated with the redundant clothing signal. Dr. Mahintamani muses that this may be a visible "cry for help."
  • “This kind of redundant clothing might be a window through which we can peep towards something really, really broken down.” (Dr. Mahintamani, 19:35)
• One poignant story details how a stranger's simple kindness (“Don’t feed the birds, just eat your food”) helps John relax enough to finally peel away his layers and touch the sand—his first moment of ease.

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3. Rejection Hurts—And Makes You Cold

[22:59–24:45]

Key Points

• Hans Isermann describes Cyberball, a psychology experiment in which participants are excluded from a ball-tossing game. In the exclusion condition:
  • People not only rate the room as colder but actually experience a measurable drop in skin temperature.
    • “It was stunning to find it...it also opened up the door for figuring out what else was there.” (Hans Isermann, 24:15)
• The bridge between emotional and literal cold/heat is established—social warmth and ostracism can literally alter bodily temperature.

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4. Body Temperature: The Myth and Meaning of 98.6

[24:53–37:41]

Key Points

• The COVID-19 pandemic made the act of taking body temperature—a “literal passport back into society.”
• Their crowdsourced temperature recordings reveal huge variance among “normal” people.
• The origin of 98.6°F is traced back to 19th-century German physician Carl Wunderlich:
  • Wunderlich’s data, later publicized/marketed by Edward Seguin and thermometer companies, burned the number into medical and cultural consciousness.
  • In reality, Wunderlich’s “average” was a statistical artifact, and his methods/focus differed from modern science.
  • “98.6—that thing we all sort of bow before—was just a little footnote from the 1800s.” (Lulu Miller, 32:03)
• Modern research (Katherine Ley, Stanford) shows:
  • No such thing as a fixed “healthy” temperature.
  • Women have higher temps than men; the young higher than the old; height, weight, time of day, hormones, and even location all matter.
  • Recent studies show that our average temperature is now closer to 97.5°F and is dropping over decades.
  • “For some people, because you’re a man, you’re old, and it’s early in the morning, coming up to 98.6 might actually be a fever for you.” (Deanna Day, 35:41)
• Despite this, people (including the hosts) still reflexively judge health or illness based on this old standard.

Memorable Moment

• Lulu, sick after a COVID shot, takes her temperature:
  • “I think my fever must be like 102...and it just comes out as 98.1. Am I a big faker?...The thermometer just said I wasn't sick.” (Lulu Miller, 36:36)

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5. The Social Life of Temperature: Networks, Emotions, and the Body

[37:57–41:25]

Key Points

• Hans Isermann’s research finds that the diversity of a person’s social network is a key predictor of their core body temperature—more types of social groups often means a higher baseline body temp.
  • Suggests our bodies register the safety of our social connections.
  • “The more kinds of groups you had, the higher your core body temperature was...” (Lulu Miller, 39:30)
• Emotional experience—loneliness, exclusion, connection—profoundly impacts our biological warmth.
• The closing montage reframes every temperature check as a possible window into a web of biological, emotional, and social truths:
  • “Did you talk to your sister? Are you on medicine? Or maybe you're off it? Do you live alone? Who do you love? Have you seen them?” (Lulu Miller, 40:47)

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Memorable Quotes

• “There’s just something so primal about the heat being more important even than the meat.”
  —Lulu Miller, [03:56]

• “Getting our warmth from another creature is super efficient. It can decrease the cost of thermoregulation by up to about 60 or 70%.”
  —Hans Isermann, [05:29]

• “I think it’s a way of shielding myself from the world...I was just doing what felt natural.”
  —John, [13:56]

• “With cold intolerance, like, you just get cold quicker.”
  —Dr. Mahintamani, [15:08]

• "This kind of redundant clothing might be a window through which we can peep towards something really, really broken down."
  —Dr. Mahintamani, [19:35]

• “98.6—that thing we all sort of bow before—was just a little footnote from the 1800s.”
  —Lulu Miller, [32:03]

• “For some people...coming up to 98.6 might actually be a fever for you. This is exactly why it’s important to not believe that a number like your temperature can tell you everything.”
  —Deanna Day, [35:41]

• **“The more kinds of groups you had, the higher your core body temperature was, the more kind.” —Lulu Miller, [39:30]

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Segment Timestamps

• [01:13–06:30] — Animal kingdom kleptothermy
• [06:51–22:22] — Human “kleptothermy”: Schizophrenia, layers, and warmth
• [22:59–24:45] — Social rejection and literal coldness (Cyberball experiment)
• [24:53–37:41] — The legend of 98.6°F: History, myth, and new science
• [37:57–41:25] — Social networks, emotion, and the biology of warmth

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Episode Takeaways

Radiolab’s "Kleptotherms" explores not just how heat moves from body to body, but how our biological drives for warmth inform, and are informed by, both our mental lives and social worlds. From evolutionary strategies to hidden signals of distress, from 19th-century big data to the pandemic’s temperature guns, the show peels back the myth of objective temperature—revealing it as a rich, shifting window into animal cunning, human loneliness, community, and care.

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Recommended for listeners curious about: The intersection of biology, society, and emotion; mental health; the cultural construction of “normal”; why warmth is never just physical.

Transcript

[A]

Hey, this is Radiolab. I'm Latif Nasser. So, at this point of the year, at least here in the Northern Hemisphere, it can start to feel like enough with the cold. Already the newness of the season has worn off. The winter holidays are over, and most of us are just ready for it to be warm again. So today we are defrosting an episode of about people and creatures seeking warmth. Sometimes they do it in obvious ways, sometimes they do it in devious ways. We first aired this episode back in 2021, and you'll hear there are certain things about it that do feel very 2021, but there's also so much in here that feels timeless. Stories that I feel confident will stay relevant until the thermal death of the universe.

[B]

Yeah, you're. Wait, you're listening. Okay.

[C]

All right.

[D]

Okay.

[C]

All right.

[E]

You're listening to Radiolab Radio Lab from wnyc.

[F]

Rewind.

[G]

Lulu? Hey, how are you feeling?

[F]

I mean, I feel fine. I think I still am, like, a dashed nasally. Hi there, it's Radiolab. I'm Lulu Miller, here with senior correspondent Molly Webster. So can you humor me and close your eyes?

[G]

Yes. Eyes closed. In my closet.

[F]

Okay, so now journey with me. Me and you are on a trip. We've got our backpacks and our hiking boots, okay? And we come across this site, an archeological dig. And they're, like, unearthing this ancient library. And we're, like, looking all around, and you're over there, and, I don't know, you find, like, a old globe. And then we come across this book that's, like, covered in dust. And we blow the dust off.

[B]

And.

[F]

The dust, like, it turns into, like, snowy, frosty snowflakes and little tiny flames. Oh, it's like. And then it says in silver letters, klep. And we were like, ooh, what's. What?

[B]

What?

[F]

And we crack the book and it's like. And we open it, and there's five chapters, and we turn the page, and the first chapter, there's just a picture of a snake in a coil. So we're going to start and read that chapter.

[G]

Okay.

[F]

So once upon a time, there was a bright blue snake in New Caledonia. It's bright blue and black, so it's just like, stretching.

[G]

Is this real?

[F]

This is real. Oh, this is one.

[G]

Okay. This is real.

[D]

Oh.

[F]

It turns out this whole book is stored in the Library of Congress as nonfiction. Okay.

[G]

Okay.

[F]

So it's this blue and black snake. It looks kind of like Betelgeuse. And it is an amphibious. It is a horrible thing. It's an amphibious sea snake, so it can live in the ocean and on land. And scientists have observed that it does.

[E]

This thing, they sneak into burrows which are occupied by large tropical seabirds.

[F]

This is Hans Isermann, a social scientist at the university Grenoble Alps, who explain that the snake will slither deeper and deeper into the burrow toward the bird, sneaking up and then it just kind of hugs it.

[E]

And they take advantage of the mass body heat in warming their own bodies.

[F]

And are they not even eating those birds? They're just kind of like curling around them and sucking up their heat.

[E]

That's essentially what they're doing? Yes.

[F]

Wow. There's just something so primal about the heat being more important even than the meat.

[E]

Yeah. So this behavior is called kleptothermy.

[G]

Kleptothermy.

[F]

And what does that mean?

[E]

Basically engaging in heat theft.

[G]

Okay.

[F]

You see it all throughout the animal kingdom.

[G]

Really?

[F]

Yeah.

[G]

Seriously?

[F]

Yeah. So like male garter snakes, they pretend.

[E]

To be female so that other males will try to mate with them.

[F]

Like the friction of them trying to mate just warms them up.

[E]

Yes.

[F]

There's little dwarf caimans, which are kind of crocodile y looking things that steal from termite nests.

[G]

How do you cuddle up to a termite?

[F]

I think you just throw yourself upon the whole warm nestiness of all that bug heat.

[E]

And us humans also engage in kleptothermy when we want to.

[F]

That oh so sweet act of cuddling, or as the scientists call it, huddling, is for at least one person involved, a theft.

[E]

I remember reading about it a couple years ago and I thought it was just fascinating. But if you think about feeds into the same kind of equation, an equation.

[F]

Biologists call the economy of action.

[E]

It's very simple. Animals need to take in more energy than they exert. And one of the most expensive things that we do, particularly as mammals, is warming our bodies.

[F]

And it turns out that of all the ways to keep our body warm, jumping up and down, finding a sunspot, eating something really fatty. Getting our warmth from another creature is super efficient.

[E]

It can decrease the cost of thermoregulation by up to about 60 or 70%.

[F]

Wow.

[E]

There are a lot of observational studies on this for many, many different animals.

[F]

Rats, penguins, degus.

[E]

Not only is their peripheral temperature higher, but also their base metabolic rate is much lower, meaning that they exert much.

[F]

Less energy to stay warm. And so Hans idea is that because for so long humans relied on getting warmth from one another to survive, even.

[E]

200 years ago, people would sleep with nine people in one bed to keep warm.

[F]

Our sense of how chilly or warm we feel isn't just about air particles. It is being influenced by the people around us way more than we typically think.

[E]

I think it's. For most people, it's hard to imagine until you see it and then you can't unsee it.

[F]

Which brings us to chapter two.

[G]

What's the picture?

[B]

I'm wearing sweatpants, a long sleeve shirt.

[F]

It's a guy in a jacket.

[B]

It's probably one of my nicer shirts. I want it to look nice, even though it's only the radio.

[F]

His name is John, and he's gonna lead us to a different idea about how to get warm.

[G]

Okay.

[B]

Okay.

[F]

Can you tell me a little bit about where you grew up?

[B]

I grew up in the woods, in a house in the woods in Connecticut.

[F]

Do you remember how the world felt to you as a kid?

[B]

Like, thinking back, me and my sister would make paths through the woods. There was a pond nearby, and we would go frogging. And I just remember playing with the hose, getting water all over us and feeling free.

[F]

But as he started to get a.

[B]

Little bit older when I was 13 or 14, things really started to change. I gained a lot of weight and everyone was, like, making fun of me. And I became very uncomfortable in my.

[F]

Skin, which, you know, happens to a lot of middle schoolers. But for John, it hit him harder.

[B]

I was scared of looking at my own reflection. I almost thought I, like, was seeing a ghost. I would keep the lights off and keep a distance from the mirror. I didn't look at the mirror for like two or three years. And then once he hit college, I started hearing voices.

[F]

And what were some of the, like, the kinds of things they might sort of be saying to you?

[B]

Do this and do that. I gotta walk in a certain fashion. And they told me that I didn't deserve to eat. It was madness. And then I saw a doctor.

[F]

Like, did you get a diagnosis then?

[B]

Yeah, schizoaffective, which is not exactly schizophrenia.

[F]

But has some of its symptoms.

[B]

He prescribed me a drug, an antidepressant. And I had a really bad reaction to it.

[F]

What happened?

[B]

It really brought on those internal voices. Like, I remember driving in the car, think, thinking everyone on the road was targeting me. So I went off my meds.

[F]

But this sense that people were out to get him just kept getting worse.

[B]

I just remember everyone giving me a hard time.

[F]

How did they give you a hard time?

[B]

They would, like, give me dirty looks. They would pull schemes on me and Mock me at times, maybe even.

[G]

Mm.

[B]

I remember my mom saying once, people aren't out to get you, and if you take your meds, then you'll realize that.

[G]

Huh.

[F]

So, like, how sure are you that you were actually being mocked and actually being given dirty looks? And how much do you think that could have been something inside you, seeing it that way?

[B]

It could have been something inside me somewhat, but it's hard for me to believe that it was all me making it up.

[F]

So he keeps just trying to muddle through. And at a certain point, John does something seemingly trivial. It's a nice, warm day out, shorts and T shirt kind of weather. And he puts on a winter hat.

[B]

I got for Christmas one year.

[F]

What color?

[B]

It was gray. It's a comfort.

[F]

And before he heads out the door, he rifles through his stuff and decides.

[B]

To also put on a hooded sweatshirt. Hood up.

[F]

And then he grabs a third layer.

[B]

It was a jacket and a fourth sweatpants.

[F]

Until eventually he's all bundled up from head to toe. And he started going out in the muggy heat of a Connecticut summer wearing this little getup all the time. And people would say things like, what.

[B]

Are you preparing for a wrestling match? Like, trying to lose weight for a wrestling. Wrestling match.

[F]

Right. Like training in trash bags kind of thing.

[B]

Yeah.

[F]

And John is the first person to say, like, as he was putting on all these layers, he was falling into this trope. Like, if you saw someone walking around in a ton of layers in the heat of summer, you're probably gonna think something's up. Maybe keep a wide berth.

[G]

Mm.

[F]

I mean, when you. When people see you wearing layers, what do you think they think about you?

[B]

I think they're fearful. They're fear. They fear me.

[C]

Hello.

[F]

Hello.

[C]

Hello.

[F]

And the thing is, while most people might step away when they see someone wearing layers, there were a few people all over the globe who decided to look closer.

[C]

Am I audible?

[F]

There you are. Sorry about that. This is Dr. Tathagata Mahintamani, a psychiatrist in India.

[C]

Currently I am in northwestern part of.

[F]

India, who, back when he was starting out as a psychiatrist in Raji, started noticing that in the middle of summer, every now and then, people with schizophrenia would walk into the hospital wearing tons of layers.

[C]

Ladies who are wearing multiple layers of sarees, and male patients who are wearing multiple layers of shirts.

[F]

And over in Melbourne, Australia, I was.

[C]

Doing my first psychiatry rotation.

[F]

Dr. Terrence Chong was treating a patient with schizophrenia.

[C]

I noticed at the time he was taking off layers and layers and layers of clothing. And this was in the Heat of summer.

[F]

There was a doctor in Memphis, Tennessee who noticed the same thing.

[G]

Wow.

[E]

Yeah.

[F]

And eventually it even got a fancy medical name.

[C]

Redundant clothing.

[F]

So the idea there is just. It's, it's redundant. You don't need it. It's. It's multiple. It's redundant. Redundant clothing.

[C]

Yes.

[F]

So a bunch of doctors were seeing this, but nobody really knew why. And some of the explanations were like, look, people with schizophrenia, some of them end up not having homes, they're living on the street. You have to keep your belongings on your back. So, like, you have. You wear them all.

[C]

Another thing might be avolition, a lack of motivation.

[F]

So basically the person maybe forgot to take the last layer off.

[C]

Yes. Yes.

[F]

Or another explanation is just this generalized erratic. I'm confused. So I have on all these clothes. I mean, there were all kinds of different explanations. Can you just describe why you crave the layers?

[B]

I think it's a way of shielding myself from the world. Like, I feel the world is harsh. It's, it's. It's hard. It's hard for me to completely put a finger on it because I was just doing what felt natural.

[F]

And Dr. Mahin Tamani, after seeing enough people walk through his door wearing layers in the heat, seemingly comfortable, wanted to figure out if something, something else was going on. So he got a group of people with schizophrenia, some of whom wore layers and some of whom didn't. And he just ran all these tests. He did, like cognitive tests and psych tests and physiological tests, and basically long, long, long, long, long story short, what he found was that the people in layers had something different going on with their blood. First of all, their blood pressure was dropping way lower on certain tests. And when he analyzed blood samples, he found that their T3 and T4 levels were lower. And what does that really mean? Like, what does that mean?

[C]

So free T3 and free T4s are very reliable markers of temperature regulation.

[F]

Temperature regulation?

[C]

Yes.

[F]

With cold intolerance, like, you just get cold quicker.

[C]

Yes. You feel cold quicker.

[G]

Wait, so they're actually. They may have layers on because they are actually physically colder.

[F]

I asked him almost exactly that. Is your idea that they are actually wearing the layers to feel warmer?

[C]

It is our findings that. And our ideas are based on our findings.

[F]

He says the evidence suggests that, like, they are wearing layers for the same reason you or I wear layers when we go out into the winter. Like their body is telling them they feel colder. Now, back in Connecticut, John didn't know any of this. He just knew that the more he Tried to stay warm by bundling. The more it pushed people away.

[B]

It was a really. It was a really difficult time for me.

[F]

And things finally got so bad that he goes back to the doctor and.

[B]

This time is, in fact, diagnosed with paranoid schizophrenia.

[F]

And he's prescribed a different medication.

[B]

I immediately noticed less up and down, less craziness. I noticed myself getting better by the day.

[F]

And the world seemed to be getting a little better, too, a little gentler.

[B]

And I felt people liked me.

[F]

And he started loosening up, literally taking off his hat.

[B]

Yeah, his jacket or one of them. It was winter, and I was. I would wear, like, a tank top under a winter jacket. And that was it.

[F]

And he started to embrace his diagnosis.

[B]

I read about how people with schizophrenic disorders oftentimes think divergently and a link to creativity.

[F]

And he would tell people about it. Like, one time he went to go buy cigarettes, and the guy behind the counter thought he looked a little young.

[B]

And I said something like, schizophrenic people tend to look young, which I don't know if it's even true, But I was very proud. I was. I wasn't very proud, but I was. I was like. I had some pride.

[F]

Call is indicating she thinks there's someone shooting in the building. And then one day, about 30 miles away from where he lives, shooting at an elementary school in Newtown, Connecticut, A young man walked into Sandy Hook Elementary School. And we all know what happened. And the day it happened, one of John's online friends sent him an instant.

[B]

Message, saying, like, when they first heard about the news that there was a shooting in Connecticut, they thought of me for an instant.

[F]

They worried the shooter had been John.

[B]

It was really hurtful. It was like, I would never do anything like that. I definitely stopped having that pride towards my diagnosis.

[F]

He stopped taking his medication.

[B]

It felt a lot more gloom and doom. And I started to slip real quickly.

[F]

Into this chilly spiral where without his meds, the world started to seem colder, which Dr. Mahin Tamani explained can be this unfortunate part of the disease that the longer you go it alone, it can have what's called a neurotoxic effect.

[C]

A neurotoxic effect on the brain, Loss of brain function, and also there is structural brain damage also there. As the time progresses, the patients with schizophrenia often, you know, drift.

[F]

So as John was drifting, the world.

[B]

Started seeming even colder, thinking everyone was targeting me.

[F]

So we'd layer up, which itself would make the world oftentimes be colder.

[B]

There was a woman walking and she just gave me the dirtiest look I've ever seen in my life. And I said to her, what is it the winter clothes that I'm wearing that makes you dislike me? And she immediately called the police.

[G]

And then it's like one more layer, another layer. Wow.

[C]

At the end of our study, we also thought that this might be a window, you know, this kind of redundant clothing might be a window through which we can. We can peep towards something really, really broken down.

[F]

Dr. Mahin Tamani found that the thing that the people who were wearing layers all had in common was that compared to the controls, they were the ones who had been going it alone without treatment for longer. That's really wild that you could just look out and, like, see that from the outside.

[C]

Yeah.

[F]

Which made me start to wonder, is it almost like humans have within them, like, this. This visual signal for, like, I'm really lost. I might not even know how to ask for help. But here is a signal that's.

[G]

That's pretty.

[F]

I mean, I put the idea to Dr. Vahitavani, and he was like, I.

[C]

Am not in a position to answer this, but this is a wonderful and intriguing question.

[G]

Yeah.

[F]

But I also put it to John. Is there anything to that, or am I, like, overly projecting an idea?

[B]

No, I think you're. You could be onto something. I think there could be, like, a cry for help through layers.

[F]

And he told me a story about one time when someone seemed to read it that way.

[B]

Well, there was one time I was at the beach, and I was having a tough day. I was wearing a sweatshirt, a beanie sweatpants, sandals. And I went and ordered a grilled cheese and French fries from this stand at the beach. And I talked to this old woman. She was probably in her late 70s, white hair, I think she was wearing a T shirt and short jean jorts.

[F]

Jordan from Old Lady Jorts?

[B]

Yeah. I said, hey, how are you? I was probably not talking that clearly and making much sense either. And she asked me if I would sit down and have lunch with her. I took a bite or two from my grilled cheese sandwich. I almost felt I didn't deserve that food. And I said to her, I think I'm gonna feed the rest of the birds. And she said to me, don't feed the birds. Just eat your food. Then I ultimately fed the birds. She went, aww. Feeling empathy towards me.

[F]

Yeah. Did you feel a little bit better after that?

[B]

Yeah, I did feel better.

[F]

He eventually felt so relaxed, he slipped off his sandals and he put his feet on the sand. And he just walked home barefoot. Yeah. Okay, so turning the page, chapter three, picture two people playing a game, sort.

[E]

Of like catch the Cyberball experiment.

[F]

Okay. So Hans, our researcher from earlier, told me about this study he did where he had people playing this game called Cyberball. And the way it works is that you enter the game and two other computer players invite you to start tossing a ball around with them. Fwoop. Fwoop. Fwoop. Fwoop.

[G]

Okay.

[F]

And then at a certain point, they just suddenly start rejecting you.

[E]

You're not part of this ball game anymore.

[F]

They just suddenly start excluding you and won't pass you the ball. And in.

[G]

That's terrible. Yeah.

[F]

And so in that, people rate, the room temperature is colder. But then what he did was he snuck onto their fingers a little digital.

[E]

Thermometer with Velcro on. It was just a bunch of sensors with a wire sticking out of it.

[F]

And he found that their peripheral skin temperature. Their skin temperature dropped in that condition when they were excluded. Yeah. And so it's like you perceive it as colder, and your skin actually gets a little colder. Huh.

[G]

Wow.

[F]

I mean, to see it reflected on the skin felt like such a leap from emotion or feeling or thought to physical reality. What was it like for you to find that result?

[E]

I think in the beginning, it was stunning to find it. I mean, I think that's also why we repeated the experiment. But it also opened up the door for kind of trying to figure out what else was there.

[F]

What else was there. After the break. This is Lulu Radiolab back here with senior correspondent Molly Webster.

[G]

Should we go back to the book?

[F]

Yeah.

[G]

Nice.

[F]

Chapter four here.

[G]

Right, Chapter four. Picture's pretty groovy. It's like a thermometer, and it's broken, and mercury is spilling out of it like blood. And I want to take chapter four.

[F]

Hell, yeah.

[G]

Well, welcome, welcome. Thank you for letting us in, because I've been thinking about this a lot lately. Like, for all of us right now, our core body temperatures, that basic temperature that our body is working at, has become a literal passport back into society. It's kind of a rainy day, so.

[F]

It might be a little bit light.

[G]

So I went to a bar in Brooklyn where, like any other bar in the city right now, there are people at the front of the bar with the gun, temperature gun, the temperature gun, zapping. Everybody who shows up deciding is people can come in and out of the door.

[F]

Oh, like the new bouncer of temperature.

[G]

Exactly. We got a 96.1. And this is happening before I go to work. Every morning, basically everywhere, I have to.

[D]

Take my temperature and text it to the school nurse.

[F]

So here we go.

[G]

We actually put a call out to our listeners, had people send us little.

[D]

Recordings to get my temperature tested as.

[G]

They headed towards work.

[B]

Arriving at Mask Sound in East Rutherford, N. Jersey.

[G]

Or to the grocery store.

[F]

I'm at my supermarket.

[B]

I'm about to go take the temperature.

[G]

Dropping their kids off at school.

[E]

Okay, Joey, let's take your temperature so.

[F]

You can go into school. Stop.

[H]

If your Temp reads above 99.4.

[G]

This is how we decide now whether or not it's okay to be around other people.

[F]

Normal temperature. You are free to pass.

[H]

Thank you.

[D]

Good to go.

[B]

See you, buddy.

[G]

Now, we did not get anybody who is in the sort of. Oh. Range. But what you do hear in the tape, 97.5, and what I saw in.

[A]

The bar, 95.5, 96, 96.3, is a.

[G]

Pretty surprising range of numbers. 97.5, 7.2 degrees.

[F]

96.4, 98.5, 95.2.

[B]

That's not right.

[G]

94.6. Little chilly, but low is better. Better than I. I mean, there were temperatures from like, maybe 92 all the way up to 98. That's six whole degrees.

[F]

Okay, so are these guns. They don't work.

[G]

Yeah.

[F]

Was that.

[G]

I mean, if there was just a study out that says the temperature guns read, like 2 to 3 degrees cooler than you actually are, which is troubling in its own right. But the thing that really hit me is that the spread of supposedly healthy people sort of flies in the face of that. That bedrock of human health. That golden number. 98.6. Yes.

[F]

The golden number of, like, what a human body should be, except it's kind of a con. A con, Sort of.

[G]

Let me just explain first where it comes from.

[F]

Okay.

[G]

So the story of 98.6 starts in the 1800s, as all good science stories do.

[F]

Yep.

[D]

So in the late 19th century, you get the introduction of thermometers into medical practice.

[G]

So for this section, I'm going to get a little help from Deanna Day.

[D]

I'm a writer and historian.

[F]

Sorry.

[G]

I got. Great, great. I always.

[D]

I have this moment because I am doing, like, 50,000 things.

[G]

She is the master of many things. But anyway, Deanna told me there's a couple of things to know about the 1800 for the purposes of our story. One is that fevers back then weren't seen as some sort of, like, signal or sign of a disease.

[D]

The fever was just the disease they thought.

[G]

Fevers were the actual illness, the thing.

[D]

You had that was causing all of your symptoms.

[F]

Like, you catch a heat and then it, like, gives you all this bad vomit, a tiredness.

[G]

But then along came a guy named Carl Wunderlich.

[F]

Cool name.

[D]

So Wunderlich was a physician in Germany.

[G]

He was the chair of medicine at the University of Leipzig. And he was one of the first people, one of the first doctors to use thermometers in his clinic at the time. They were like 2ft long and took 20 minutes to take a temperature. And in the 1850s, when Wunderlich was doing his thing, it was like an era when big data was becoming king. Which is funny because you wouldn't actually think about that because there were no computers or.

[F]

Lots of pencils.

[G]

Yeah, lots of pencils, lots of paper. And so his thing that he was like, okay, the data that I'm gonna collect is I wanna understand how temperature of a human body changes throughout the progression of an illness.

[D]

And so at his hospital, they took temperature readings repeatedly, over and over from about 25,000 patients.

[G]

25,000 patients. A million and a half temperature recordings.

[F]

Did he have a fleet of temperature collectors?

[G]

No, it was basically him and whoever worked in his clinic. He just had a really busy clinic in Germany.

[F]

Wow, that's like. That feels. But I guess over, like, decades, right?

[G]

Yeah, like 20 years. So Wunderlich collects all this data and.

[D]

Did the 19th century version of crunching the numbers and created all of these charts, fever charts. He found different diseases had different fever progressions in patients.

[G]

He would have, like, a patient that had syphilis, say, and he could map their temperature change throughout syphilis. And he would get, like, a really pretty pattern on an XY graph.

[D]

Some diseases would have a fever that would spike and drop and spike and drop. And other diseases had a fever course that would kind of like, ramp up gradually or ramp down slowly.

[F]

Really cool. I've never thought of that. Like that. That each illness has a little curlicue signature that you're like, I know.

[G]

Oh, that's cool, if I'm honest. Like, I don't know if that actually still holds up today.

[F]

Yeah.

[D]

But his idea was that you could track someone's temperature and. And diagnose them that way. And that was a big change.

[G]

All of a sudden, we start seeing fever not as something that comes at you from the outside, but something that your body does on the inside when it's reacting to a disease. And this is how we get to a place where we can gun someone and say, oh, you're sick, stay away. Anyways, he publishes it all in this big book.

[D]

And kind of incidentally, he was like, and in healthy people, when they are no longer sick, we have found that body temperature is 37 degrees Celsius, which.

[G]

Is the conversion to Fahrenheit is 98.6.

[F]

Interesting. So he was just like, oops, I was studying this other thing. I accidentally have a cash million data points.

[G]

Yeah. It was essentially a footnote.

[F]

98.6. That thing we all sort of built bow before was just a little footnote from the 1800s.

[G]

Well, yes, until this guy came along named Edward Seguin.

[D]

Edward Seguin is the person who actually translated Wunderlich's work and introduced it to the United States.

[G]

And he's really into thermometry, which is a word. It was just a word. I know.

[D]

He writes this manual called Family Thermometry, which is supposed to teach moms how to take their kid's temperature and why it's important and how to do it.

[G]

And so Seguin, along with thermometer companies, kind of went on this big push.

[D]

Through, like, articles in Good Housekeeping and Ladies Home Journal and Scientific American to.

[G]

Talk about thermometers and make them like a new tool for the home.

[D]

And there are advertisements in all kinds.

[G]

Of publications, and over and over again, they'd hammer on this number. 98.6. 98.6. That's what you should be. That's what your kids should be. And I feel like this, like, marketing campaign that happened at the end of the 1800s and the early 1900s is essential, essentially been handed down to us through the century and made us think that 98.6 is the normal or ideal temperature for a human body, which is bull. Well, it turns out that there's a.

[D]

Lot of variation across all these different parameters.

[G]

So this is Katherine Ley, infectious disease.

[D]

Epidemiologist at Stanford University.

[G]

And as Kat explained it to me, there is no one healthy human temperature.

[D]

Women have higher temperatures than men. Bigger people have higher temperatures.

[G]

Fatter and skinnier people have different temperatures.

[D]

Taller people have lower temperatures.

[F]

Whoa.

[G]

They're just so thinned out that they got surface area for days. I don't know. Hormones can change your temperatures. Morning and night can change your temperatures.

[D]

Younger people have higher temperatures than older people.

[F]

I'm already thinking about the sweatsuits. I want to rock. Okay.

[G]

And even in the same person, temperature taken in the ear, in your armpit, and your butt can vary by, like, 2 degrees mo. Now, all this variation piles up to an average of 98.6. But just to really crack this thermometer wide open. And you might remember this from the episode I did last summer. Fungus among us researchers don't even think 98.6 is. Are average anymore.

[F]

What?

[G]

Like, there was just a new paper a year ago that said it looks like the sort of average of a. Of a healthy kind of Western population is 97.5. And Kat was actually involved in that research, and she said that it looks like our temperature has been dropping 0.05 degrees Fahrenheit every decade since the 1850s.

[B]

Whoa.

[G]

There's a number of reasons they think that might be the case. Like, maybe we have better medicines so we're not fighting infections as much. You know, maybe it's just the fact that we are older and taller.

[F]

You know, even the average is. I mean, I remember that episode. I was so focused on the scary fungus that I feel like I missed the major drawbacks.

[G]

It was just slipped in there, you know?

[F]

But it's like you're saying, so not only is there all this individuality on person and time of day and part of body, but then also. Oh, and also the average isn't the average either.

[G]

Yeah. So much so that for some people, because you're a man, you're old, and it's early in the morning, coming up.

[D]

To 98.6 might actually be a fever for you. This is exactly why it's important to not believe that a number like your temperature can tell you everything.

[G]

But even when you know that, it's so hard to let go of that number. I just got the COVID vaccine yesterday, and I feel so rough. So I had this moment where, like, I got my Covid vaccination, my second one, and it, like, laid me low. So, so, so achy. And in the middle of that, I thought I should take my temperature. I was super achy, and I really hurt, and so I, you know, turned on my voice memo. It hurts so bad, and my voice is ridiculous, and I think my fever must be like, 102. And I take my temperature and it just 98.1 comes out as 98.1.

[F]

Oh.

[G]

And I was just like, oh, am.

[F]

I a big faker?

[G]

Yeah. Am I making this worse than it is? Like, the thermometer just said I wasn't sick. And then I like, no one at Radiolab's gonna believe me. The thermometer can't be right because it doesn't encapsulate how terrible. Despite knowing everything I like, just while.

[F]

You'Re in the midst of this reporting, I'm.

[G]

In the midst of this reporting, you.

[F]

Were still, like, measuring yourself up against that number six.

[G]

And so it's like all of that against me. And then in the middle of sort of like the fever haze, the non fever haze, the non fever fever haze, I'm like, kind of hanging off the side of my bed, like, very pathetic. And I was just like, this is just like what Deanna said.

[D]

I think that acting as if fever as a quantitative measure can give you objective truth just makes it impossible for you, not you. Makes it impossible for anyone to see the full scope of what is happening inside a person.

[G]

I definitely felt that in that moment, taking my own temperature. But. But I think I also realized that you can actually throw out the 98.6 thing, and then your temperature, whatever it is, can be a window into so much more about a person, like how old you are, what your hormones are, or whether you live in a place with adequate medical care.

[F]

Can I add one more kind of eerie one, of course, of what your temperature might be able to tell you? So Hans, our researcher from before, he actually did a study where he wanted to see what predicted core body temperature. So he plugged in all these variables. Age, height, weight, location, distance from equator, cigarette consumption, sugary drink consumption, perceived level of stress, any medications, access to a cell phone. Like, tons and tons of tons of things. And this thing that was right up near the top. More important than body weight or height was diversity of your social network. And so what that means is, like, not how many friends you have, but how many different kinds. So, like, do you have your work?

[G]

Oh, it's not number. It's groups.

[F]

Yes. It's like your work friends and your soccer friends and your knitting friends and your extended family and the Webster sisters. And so, like, the more kinds of groups you had, the higher your core body temperature was, the more kind.

[G]

How do you. Does he have any explanation for that?

[F]

I think the. I mean, he doesn't know. Like, he doesn't know exactly what that means, but I think there's some idea of, like, if one type bails on you, the more types of backups you have, the safer your body, the less at risk your body feels.

[G]

It's just there's this very porous border between what I thought of as a very physiological thing, which is your body temperature, to what's happening mentally and emotionally in your brain. Like emotions tuning your body temperature to what it is.

[F]

Yeah.

[G]

Which makes me think back on that temperature check tape a little differently.

[F]

Like, can I take your temperature?

[B]

Yeah, sure.

[D]

Normal temperature.

[G]

96.1. Did you gain weight?

[B]

97.5.

[F]

96.4.

[G]

What time of day is it?

[F]

Temperature is normal.

[G]

96. Maybe you're pregnant.

[F]

97.2 degrees.

[G]

97.7. Have you seen a doctor night?

[F]

97.7.

[G]

Did a stranger wave at you on the street? 95.4. 96.3.

[D]

Normal temperature.

[G]

Did you talk to your sister? Are you on medicine? Or maybe you're off it? Do you live alone? Who do you love? Have you seen them?

[F]

Molly Webster this episode was produced by Becca Bressler, Molly Webster and me, with production help from Karen Leong and and fact checking by Emily Krieger. Hans Eserman has a new book about a lot of the science we covered in this hour called How Our Inner Thermostat Made Us Human. Special thanks to Tony Bartlumay, Julie Parsonet, Philip Mackowiak, Carla Hawk, Lacy Alexander, Anna Stanowitz, Brendan and all the folks over at the Commissioner in Park Slope, our listeners, for their voice memos. Thank you, thank you, thank you. Temperature, temperature, temperature. And last big one to Invisibilia. I first started talking to John back when I was working with them and they let me use some of that audio. I really recommend you go check it out. Thanks for listening.

[H]

Hi, I'm Eric Baum and I'm from Minneapolis, Minnesota. And here are the staff credits. Radiolab is hosted by Lulu Miller and Latif Nasser. Soren Wheeler is our Executive editor. Sarah Sandbach is our executive executive director. Our managing editor is Pat Walters. Dylan Keefe is our director of Sound design. Our staff includes Jeremy Bloom, W. Harry Fortuna, David Gable, Maria Paz Gutierrez, Sindhu Nayasambadan, Matt Kilty, Mona Madgawker, Annie McEwen, Alex Neeson, Sara Kari, Rebecca Rand, Anisa Vitza, Arianne Wack, Molly Webster and Jessica Young. Our fact checkers are Diane Kelly, Emily Krieger, Natalie Middleton, Angeli Mercado and Sophie Semei.

[F]

Leadership support for Radiolab's science programming is provided by the Simons foundation and the John Templeton Foundation. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation.