[RADIOLAB INTRO]

MOLLY WEBSTER: Lu!

LULU MILLER: Hey!

MOLLY: How are you feeling?

LULU: I mean, I feel fine. I think I still am, like, a dash nasally.

LULU: Hi there. It's Radiolab. I'm Lulu Miller, here with senior correspondent Molly Webster.

LULU: So can you humor me and close your eyes?

MOLLY: Yes, eyes closed in my closet.

LULU: Okay, so now journey with me. Me and you are on a trip. We've got our backpacks and our hiking boots.

MOLLY: Okay.

LULU: And we've—we come across this site, an archaeological 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, an old globe. And then we come across this book that's, like, covered in dust. And we blow the dust off. [blows] And the dust, like, it turns into, like, snowy, frosty snowflakes and little, tiny flakes.

MOLLY: Oh!

LULU: It's like [blows] And then it says in silver letters, "Kleptotherms." And we were, like, "Ooh! What's—what? What?" 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 gonna start and read that chapter.

MOLLY: Okay.

LULU: 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, striped. It looks ...

MOLLY: Is this real?

LULU: This is real. Oh, this is one ...

MOLLY: Okay. This is—okay, this is real.

LULU: Oh, it turns out this whole book ...

MOLLY: [laughs]

LULU: ... is stored in the Library of Congress as nonfiction. Okay.

MOLLY: Okay.

LULU: So it's this blue and black snake. It looks kind of like Beetlejuice. And it is a—and it's 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 this thing.

HANS IJZERMAN: They sneak into burrows which are occupied by large tropical seabirds.

LULU: This is Hans Ijzerman, a social scientist at the Université Grenoble Alpes, who explained that the snake will slither deeper and deeper into the burrow, towards the bird, sneaking up. And then it just kind of hugs it.

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

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

HANS IJZERMAN: That's essentially what they're doing, yes.

LULU: Wow [laughs]. There's just something so primal about the heat being more important even than the meat.

HANS IJZERMAN: [laughs Yeah. So this behavior is called kleptothermy.

LULU: Kleptothermy. And what does that mean?

HANS IJZERMAN: Basically engaging in heat theft.

LULU: Okay.

LULU: You see it all throughout the animal kingdom, kleptothermy.

MOLLY: Really?

LULU: Yeah. So, like ...

MOLLY: Seriously?

LULU: Yeah. So, like, male garter snakes ...

HANS IJZERMAN: They pretend to be female so that other males will try to mate with them.

LULU: Like, the friction of them trying to mate just warms them up?

HANS IJZERMAN: Yes.

LULU: There's little dwarf caimans, which are kind of like crocodiley-looking things that steal from termite nests.

MOLLY: How do you cuddle up to a termite?

LULU: I don't know.

MOLLY: You just [laughs] ...

LULU: You just, like—I think you, like ...

MOLLY: You just get in there.

LULU: You just, like, throw yourself upon the whole warm nestiness of all that bug heat.

MOLLY: Wow!

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

LULU: That oh so sweet act of cuddling, or as the scientists call it ...

HANS IJZERMAN: Huddling.

LULU: ... is, for at least one person involved, a theft.

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

LULU: An equation biologists call the economy of action.

HANS IJZERMAN: 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.]

LULU: 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.

HANS IJZERMAN: It can decrease the cost of thermoregulation by up to about 60 or 70 percent.

LULU: Wow!

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

LULU: Rats, penguins, degus.

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

LULU: To stay warm.

MOLLY: Huh.

LULU: And so Hans' idea is that because for so long humans relied on getting warmth from one another to survive ...

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

LULU: ... 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.

HANS IJZERMAN: I think it's—for most people, it's hard to imagine until you see it. And then you can't unsee it.

LULU: Which brings us to Chapter two.

MOLLY: What's the picture?

JOHN: I'm wearing sweatpants, a long-sleeved shirt.

LULU: It's a guy in a jacket.

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

LULU: [laughs]

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

MOLLY: Okay.

JOHN: Okay.

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

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

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

JOHN: 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.

LULU: But as he started to get a little bit older ...

JOHN: 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 skin.

LULU: Which, you know, happens to a lot of middle schoolers. But for John, it hit him harder.

JOHN: I was scared of looking—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.

LULU: And then once he hit college ...

JOHN: I started hearing voices.

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

JOHN: Do this, and do that. I've 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.

LULU: Like, well, did you get a diagnosis then?

JOHN: Yeah. Schizoaffective.

LULU: Which is not exactly schizophrenia, but has some of its symptoms.

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

LULU: What happened?

JOHN: It really brought on those internal voices. Like, I remember driving in the car thinking everyone on the road was targeting me.

LULU: So ...

JOHN: I went off my meds.

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

JOHN: I just remember everyone giving me a hard time.

LULU: How did they give you a hard time?

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

LULU: Hmm.

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

LULU: Huh. 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?

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

LULU: 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.

JOHN: I got it for Christmas one year.

LULU: What color?

JOHN: It was gray. It's a comfort.

LULU: And before he heads out the door, he rifles through his stuff and decides to also put on ...

JOHN: ...A hooded sweatshirt, hood up.

LULU: And then he grabs a third layer.

JOHN: It was a jacket.

LULU: And a fourth.

JOHN: Sweatpants.

LULU: 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 ...

JOHN: What, are you preparing for a wrestling match? Like, trying to lose weight for a wrestling match?

LULU: Right. Right. Like, training in trash bags kind of thing.

JOHN: Yeah.

LULU: 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.

MOLLY: Mm-hmm.

LULU: I mean, when you—when people see you wearing layers, what do you think they think about you?

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

TATHAGATA MAHINTAMANI: Hello?

LULU: Hello.

TATHAGATA MAHINTAMANI: Hello.

LULU: 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.

TATHAGATA MAHINTAMANI: Am I audible?

LULU: There you are. Sorry about that.

LULU: This is Dr. Tathagata Mahintamani, a psychiatrist in India.

TATHAGATA MAHINTAMANI: Currently, I am in northwestern part of India.

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

TATHAGATA MAHINTAMANI: Ladies were wearing multiple layers of saris, and male patients who are wearing multiple layers of shirts.

LULU: And over in Melbourne, Australia ...

TERENCE CHONG: I was doing my first psychiatry rotation.

LULU: ... Dr. Terence Chong was treating a patient with schizophrenia.

TERENCE CHONG: I noticed at the time he was taking off layers and layers and layers of clothing. And this was in the heat of summer.

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

MOLLY: Wow.

LULU: Yeah. And eventually it even got a fancy medical name.

TATHAGATA MAHINTAMANI: Redundant clothing.

LULU: So the idea there is just it's—you don't need it. It's multiple. It's redundant, redundant clothing.

TATHAGATA MAHINTAMANI: Yes.

LULU: 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.

TATHAGATA MAHINTAMANI: Another thing might be avolition.

LULU: A lack of motivation. So basically, the person maybe forgot to take the last layer off.

TATHAGATA MAHINTAMANI: Yes, yes. Or ...

LULU: 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.

LULU: Can you just describe why you crave the layers?

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

LULU: And Dr. Mahintamani, after seeing enough people walk through his door wearing layers in the heat, seemingly comfortable, wanted to figure out if 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, a 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.

LULU: And what does that really mean? Like, what does that mean?

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

LULU: Temperature regulation?

TATHAGATA MAHINTAMANI: Yes, with cold intolerance.

LULU: Like, you just get cold quicker?

TATHAGATA MAHINTAMANI: Yes.

LULU: Okay.

TATHAGATA MAHINTAMANI: Yes, you'll feel cold quicker.

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

LULU: I asked him almost exactly that.

LULU: Is your idea that they are actually wearing the layers to feel warmer?

TATHAGATA MAHINTAMANI: It is our findings that [laughs] ...

LULU: [laughs]

TATHAGATA MAHINTAMANI: Not—and our ideas are based on our findings.

LULU: 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.

MOLLY: Whoa!

LULU: 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.

JOHN: It was a really difficult time for me.

LULU: And things finally got so bad that he goes back to the doctor, and this time is, in fact, diagnosed with ...

JOHN: Paranoid schizophrenia.

LULU: And he's prescribed a different medication.

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

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

JOHN: And I felt people liked me.

LULU: And he started loosening up, literally. Taking off his hat ...

JOHN: Yeah.

LULU: ... his jacket ...

JOHN: [laughs] Well ...

LULU: ... or one of them.

JOHN: It was winter. And I was—I would wear, like, a tank top under a winter jacket, and that was it.

LULU: And he started to embrace his diagnosis.

JOHN: I read about how people with schizophrenic disorders oftentimes think divergently, and it's a link to creativity.

LULU: 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.

JOHN: 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—like, I had some pride.

[ARCHIVE CLIP, police radio: Caller's indicating she thinks that someone's shooting in the building.]

LULU: And then one day, about 30 miles away from where he lives ...

[NEWS CLIP: ... shooting at an elementary school in Newtown, Connecticut, and you ...]

LULU: ... 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 message saying ...

JOHN: Like, when they first heard about the news that there was a shooting in Connecticut, they thought of me.

LULU: For an instant, they worried the shooter had been John.

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

LULU: He stopped taking his medication.

JOHN: I felt a lot more gloom and doom, and I started to slip real quickly.

LULU: Into this chilly spiral, where without his meds, the world started to seem colder, which Dr. Mahintamani 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.

TATHAGATA MAHINTAMANI: A neurotoxic effect on the brain.

LULU: Hmm.

TATHAGATA MAHINTAMANI: 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.

LULU: So as John was drifting, the world started seeming even colder.

JOHN: Thinking everyone was targeting me.

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

JOHN: 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.

MOLLY: And then it's like one more layer.

LULU: Another layer.

MOLLY: Wow.

TATHAGATA MAHINTAMANI: At the end of our study, we also thought that this is—this might be a window, you know? This kind of redundant clothing might be a window through which we can peep towards something really, really broken down.

LULU: Dr. Mahintamani 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.

LULU: That's really wild that you could just look out and, like, see that from the outside.

TATHAGATA MAHINTAMANI: Yeah.

LULU: Which made me start to wonder, is it almost like humans have within them, like, this visual signal for, like, I'm really lost, I might not even know how to ask for help, but here is a signal?

MOLLY: Hmm. That's pretty ...

LULU: I mean, I put the idea to Dr. Mahintamani, and he was like ...

TATHAGATA MAHINTAMANI: I am not in a position to answer this, but this is a wonderful and intriguing question.

LULU: Yeah.

LULU: But I also put it to John.

LULU: Is there anything to that, or am I, like, overly projecting an idea?

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

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

JOHN: 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 or whatever they're called.

LULU: Jorts, some old lady jorts?

JOHN: Yeah. And I said, "Hey, how are you?" And 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 to the birds." And she said to me, "Don't feed the birds. Just eat your food." [laughs] And then I ultimately fed the birds. She went, "Aww!" Like, feeling empathy towards me.

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

JOHN: Yeah, I did feel better.

LULU: He eventually felt so relaxed he slipped off his sandals, and he put his feet on the sand, and he just walked home barefoot.

JOHN: Yeah.

LULU: Okay, so turning the page. Chapter three. Picture two people playing a game sort of like catch.

HANS IJZERMAN: The Cyberball Experiment.

LULU: 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. Voop, voop, voop, voop.

MOLLY: Okay.

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

HANS IJZERMAN: You are not part of this ball game anymore.

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

MOLLY: That's terrible.

LULU: Yeah. And so, like, in that, people rate the room temperature as colder. But then what he did was he snuck onto their fingers a little digital thermometer.

HANS IJZERMAN: With Velcro on it. It was just a bunch of sensors with a wire sticking out of it.

LULU: And he found that their peripheral skin temperature, their skin temperature dropped in that condition when they were excluded.

MOLLY: What? No way!

LULU: Yeah. And so it's like you perceive it as colder.

MOLLY: That's super cool.

LULU: And your skin actually gets a little colder.

MOLLY: Huh. Wow!

LULU: 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?

HANS IJZERMAN: 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 it kind of trying to figure out what else was there.

LULU: What else was there, after the break.

[LISTENER: Hey, my name's Laurel. I'm calling from London. 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 Sloan at www.sloan.org.]

[JAD ABUMRAD: Science reporting on Radiolab is supported in part by Science Sandbox, a Simons Foundation initiative dedicated to engaging everyone with the process of science.]

LULU: This is Lulu. Radiolab. Back here with senior correspondent Molly Webster.

MOLLY: Should we go back to the book?

LULU: Yeah.

MOLLY: Nice!

LULU: Chapter four here, right?

MOLLY: Chapter four. Picture's pretty groovy. It's like a thermometer, and it's broken and mercury is spilling out of it like blood.

LULU: Ooh!

MOLLY: And I want to take chapter four.

LULU: Hell, yeah.

DOORMAN: Welcome. welcome.

MOLLY: Thank you for letting us in.

MOLLY: Because I've been thinking about this a lot lately. Like, for all of us right now, our core body temperature, that basic temperature that our body is working at, has become a literal passport back into society.

DOORMAN: It's kind of a rainy day, so it might be a little bit light.

MOLLY: 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.

DOORMAN: Temperature gun.

MOLLY: The temperature gun.

MOLLY: Zapping everybody who shows up.

DOORMAN: Bunny and Scott have got it under control.

MOLLY: Deciding if people can come in and out of the door.

LULU: Oh, like the new bouncer of temperature.

MOLLY: Exactly.

[beep]

BUNNY: We got a 96.1.

MOLLY: And this is happening ...

WOMAN: Before I go to work every morning ...

MOLLY: ... basically everywhere.

WOMAN: ... I have to take my temperature and text it to the school nurse. So here we go.

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

WOMAN: I'm walking up to get my temperature tested where I tutor.

MOLLY: ... as they headed to work ...

MAN: Arriving at Masque Sound in East Rutherford, New Jersey.

MOLLY: ... or to the grocery store.

MAN: I'm at my supermarket. I'm about to go take the temperature.

MOLLY: Dropping their kids off at school.

MAN: Okay, Joey. Let's take your temperature so you can go into school.

MAN: Stop if your temp reads above 99.4.

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

WOMAN: Normal temperature. You are free to pass.

MAN: Thank you.

WOMAN: Good to go.

MAN: See you, buddy.

MOLLY: Now we did not get anybody who was in the sort of uh-oh range, but what you do hear in the tape ...

MAN: 97.5.

MOLLY: ... and what I saw in the bar ...

MAN: 95.5.

WOMAN: 96.

MAN: 96.3.

MOLLY: ... is a pretty surprising range of numbers.

WOMAN: 97.5!

MAN: 97.2 degrees.

WOMAN: 96.4.

WOMAN: 98.5.

MAN: 95.2. That's not right.

WOMAN: 94.6. It's a little chilly, but low is better than high.

MOLLY: I mean, there were temperatures from, like, maybe 92 all the way up to 98. That's six whole degrees.

LULU: Okay, so are these guns—they don't work.

MOLLY: [laughs] Yeah.

LULU: Was that—I mean, if ...

MOLLY: Well, there was just a study out that says the temperature guns read, like, two to three degrees cooler than you actually are.

LULU: Dude, okay.

MOLLY: 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 bedrock of human health, that golden number, 98.6.

LULU: Yes, the golden number of, like, what a human body should be.

MOLLY: Except it's kind of a con.

LULU: A con?

MOLLY: Sort of. Let me just explain first where it comes from.

LULU: Okay.

MOLLY: So the story of 98.6 starts in the 1800s, as all good science stories do. [laughs]

LULU: Yup.

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

MOLLY: So for this section, I'm gonna get a little help from Deanna Day.

DEANNA DAY: I'm a writer and historian. [laughs] Sorry. I got ...

MOLLY: Great, great.

DEANNA DAY: [laughs] I always—I have this moment because I am doing, like, 50,000 things.

MOLLY: She is the master of many things. But anyway, Deanna told me there's a couple of things to know about the 1800s 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.

DEANNA DAY: The fever was just the disease.

MOLLY: They thought fevers were the actual illness.

DEANNA DAY: The thing you had that was causing all of your symptoms.

LULU: Like, you catch a heat, and then it, like, gives you ...

MOLLY: Yeah.

LULU: ... all this bad vomit-y tiredness.

MOLLY: Yeah. But then along came a guy named Carl Wunderlich.

LULU: Cool name.

DEANNA DAY: So Wunderlich was a physician in Germany, and ...

MOLLY: 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 two feet 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.

LULU: There were lots of pencils.

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

LULU: Hmm.

MOLLY: And so ...

DEANNA DAY: At his hospital, they took temperature readings repeatedly over and over from about 25,000 patients.

MOLLY: 25,000 patients, a million and a half temperature recordings.

LULU: Did he have a fleet of temperature collectors?

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

LULU: Wow! That's like—that feels—but I guess over, like, decades, right?

MOLLY: Yeah. Like, 20 years. So Wunderlich collects all this data. And ...

DEANNA DAY: Did the 19th century-version of crunching the numbers, and created all of these charts.

MOLLY: Fever charts.

DEANNA DAY: He found different diseases had different fever progressions in patients.

MOLLY: He would have, like, a patient that had syphilis, say.

LULU: Mm-hmm.

MOLLY: And he could map their temperature change throughout syphilis. And he would get, like, a really pretty pattern on an X, Y graph.

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

MOLLY: Really?

LULU: Cool. I never thought of that, like, that each illness has a little curlicue signature that you're, like ...

MOLLY: I know.

LULU: Oh, that's cool!

MOLLY: If I'm honest, like, I don't know if that actually still holds up today.

LULU: Yeah.

MOLLY: But ...

DEANNA DAY: His idea was that you could track someone's temperature and diagnose them that way. And that was a big change.

MOLLY: 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 ...

[beep]

MOLLY: ... gun someone and say, "Oh, you're sick. Stay away."

LULU: Hmm.

MOLLY: Anyways, he publishes it all in this big book.

DEANNA DAY: 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."

MOLLY: Which is—the conversion to Fahrenheit is 98.6.

LULU: Interesting. So he was just like, "Oops, I was studying this other thing. I accidentally have a kaj-million data points.

MOLLY: Yeah. It was essentially a footnote.

LULU: 98.6, that thing we all sort of bow before, was just a little footnote from the 1800s?

MOLLY: Well, yes. Until this guy came along named Édouard Séguin.

DEANNA DAY: Édouard Séguin is the person who actually translated Wunderlich's work and introduced it to the United States.

MOLLY: And he's really into thermometry.

LULU: Which is a word.

MOLLY: Which is a word. I know.

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

MOLLY: And so Séguin, along with thermometer companies, kind of went on this big push through, like ...

DEANNA DAY: Articles in Good Housekeeping and Ladies' Home Journal and Scientific American.

MOLLY: ... to talk about thermometers and make them, like, a new tool for the home.

DEANNA DAY: And there are advertisements in all kinds of publications.

MOLLY: 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 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 [bleep].

LULU: [laughs]

CATHERINE LEI: Well, it turns out that there's a lot of variation across all these different parameters.

MOLLY: So this is Catherine Lei.

CATHERINE LEI: Infectious disease epidemiologist at Stanford University.

MOLLY: And as Cat explained it to me, there is no one healthy human temperature.

CATHERINE LEI: Women have higher temperatures than men. Bigger people have higher temperatures.

MOLLY: Fatter and skinnier people have different temperatures.

CATHERINE LEI: Taller people have lower temperatures.

LULU: Whoa!

MOLLY: They're just so thinned out that they got surface area for days?

CATHERINE LEI: [laughs] I don't know.

MOLLY: Hormones can change your temperatures. Morning and night can change your temperatures.

CATHERINE LEI: Younger people have higher temperatures than older people.

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

MOLLY: And even in the same person, temperature taken in the ear, in your armpit and your butt can vary by, like, two degrees.

LULU: Wow!

MOLLY: 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 Amungus—researchers don't even think 98.6 is our average anymore.

LULU: What?

MOLLY: Like, there was just a new paper a year ago that said it looks like the sort of average of a healthy kind of Western population is 97.5. And Cat 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.

LULU: Whoa!

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

LULU: So 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 temperature drop.

MOLLY: I mean, it was just slipped in there, you know?

LULU: 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 ...

MOLLY: [laughs]

LULU: Oh, and also the average isn't the average either.

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

CATHERINE LEI: Coming up to 98.6 might actually be a fever for you.

DEANNA DAY: This is exactly why it's important to not believe that a number like your temperature can tell you everything.

MOLLY: But even when you know that, it's so hard to let go of that number.

MOLLY: I just got the COVID vaccine yesterday, and I feel so rough.

MOLLY: So I had this moment where, like, I got my COVID vaccination, my second one, and it, like, laid me low.

MOLLY: So, so, so achy.

MOLLY: 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 ...

MOLLY: And it's so bad.

MOLLY: And my voice is ridiculous. And I think my fever must be like 102. And I take my temperature and it just ...

MOLLY: 98.1.

MOLLY: ... comes out as 98.1.

LULU: Oh.

MOLLY: And I was just like, oh [bleep]. Am I ...

LULU: A big faker?

MOLLY: 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.

MOLLY: I—the thermometer can't be right because it doesn't encapsulate how terrible I feel. [laughs]

MOLLY: Despite knowing everything I just told you ...

LULU: Despite, like, this is while you're in the midst of this reporting?

MOLLY: Yeah, I'm in the midst of this reporting.

LULU: You were still, like, measuring yourself up against that number?

MOLLY: On 98.6. And so it's like that against—against me. And then in the middle of sort of, like, the fever haze [laughs]—the non-fever haze, the not 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."

DEANNA DAY: 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.

MOLLY: I definitely felt that in that moment taking my own temperature, 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, you know, whether you live in a place with adequate medical care.

LULU: Can I add one more kind of eerie one ...

MOLLY: Of course.

LULU: ... 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 ...

MOLLY: Ooh!

LULU: ... perceived level of stress, any medications, access to a cell phone. Like, tons and tons and tons of things. And the 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 ...

MOLLY: Yeah.

LULU: ... different kinds. So, like, do you have your work ...

MOLLY: Oh, it's not number, it's, like, groups or something.

LULU: 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.

MOLLY: The more—how do you—does he have any explanation for that?

LULU: 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.

MOLLY: 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.

LULU: Yeah.

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

WOMAN: Can I take your temperature?

MAN: Yeah, sure.

COMPUTERIZED VOICE: Normal temperature.

WOMAN: 96.1.

MOLLY: Did you gain weight?

MAN: 97.5.

WOMAN: 96.4.

MOLLY: What time of day is it?

[beep]

COMPUTERIZED VOICE: Temperature is normal.

WOMAN: 96.

MOLLY: Maybe you're pregnant.

MAN: 97.2 degrees.

[beep]

WOMAN: 97.7.

MOLLY: Have you seen a doctor?

WOMAN: 97.7.

MOLLY: Did a stranger wave at you on the street?

WOMAN: 95.4.

MAN: 96.3.

COMPUTERIZED VOICE: Normal temperature.

[beep]

MOLLY: Did you talk to your sister?

WOMAN: 97.5.

MOLLY: Are you on medicine?

COMPUTERIZED VOICE: Temperature is normal.

MAN: 95.5.

[beep]

MOLLY: Or maybe you're off it.

COMPUTERIZED VOICE: Temperature check.

MOLLY: Do you live alone?

[beep]

MOLLY: Who do you love?

[beep]

MOLLY: Have you seen them?

[beep]

LULU: Molly Webster. This episode was produced by Becca Bressler, Molly Webster and me, with production help from Carin Leong and fact-checking by Emily Krieger. Hans IJzerman has a new book about a lot of the science we covered in this hour called Heartwarming: How Our Inner Thermostat Made Us Human. Special thanks to Tony Bartolome, Julie Parsonnet, Philip Mackowiak, Karla Haack, Lacey Alexander, Anna Stankiewicz, 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. And while I have your ears, Invisibilia has a new season out with new hosts Yowei Shaw and Kia Natisse. It is so good. And if you listen really close, you can hear the sounds of a show molting into something bigger, more beautiful and braver than anything we ever could have imagined when we first started out. I really recommend you go check it out. Thanks for listening.

[LISTENER: Hi, this is Jonathan Chan calling in from Singapore. Radiolab was created by Jad Abumrad and is edited by Soren Wheeler. Lulu Miller and Latif Nasser are our co-hosts. Suzie Lechtenberg is our executive producer. Dylan Keefe is our director of sound design. Our staff include Simon Adler, Jeremy Bloom, Becca Bressler, Rachael Cusick, David Gebel, Matt Kielty, Annie McEwen, Sarah Qari, Arianne Wack, Pat Walters and Molly Webster, with help from Shima Oliaee, Sarah Sandbach and Carin Leong. Our fact-checkers are Diane Kelly and Emily Krieger.]

LULU: Okay, so remember I said this book does have a fifth chapter?

MOLLY: Ooh!

LULU: The picture is just a scale in perfect balance.

MOLLY: Okay.

LULU: So you know how, like, there's a kind of gnarliness to the concept of theft? Like, kleptothermy? This is all about how, like, we are ...

MOLLY: We're stealing something.

LULU: Yeah. It's like that equation: you've gotta take in more than you give.

MOLLY: Mm-hmm.

LULU: And if you don't get enough, you feel wounded and at risk.

MOLLY: Yeah.

LULU: And if you are getting enough, you're stealing it from someone or something else. Like, if we got to an equilibrium, wouldn't that be so nice?

MOLLY: Yes, equilibrium would be—so we're just—we're all giving and taking and, like, coexisting, and it's a balance. Yeah.

LULU: Okay. Do you know what that's called? You know what the physicists call that?

MOLLY: No.

LULU: The thermal death ...

MOLLY: Wait ...

LULU: ... of the universe.

MOLLY: Wait. Equilibrium is thermal death?

LULU: Yeah. Like, there will be a time when everything becomes the same temperature, and that is the end. I don't know.

MOLLY: I will be grateful for the give-and-take.

LULU: Be grateful for the give-and-take. We will give you away to your life. That's the end. See you next time.

MOLLY: [laughs]

LULU: Thanks for listening. Bye.

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