[RADIOLAB INTRO]

LULU MILLER: Back in the chair, Latif.

LATIF NASSER: I'm so excited we finally get to do this together! Hey, it's Latif Nasser!

LULU: And Lulu Miller!

LATIF: And this is Radiolab. Hey, welcome back.

LULU: Thank you!

LATIF: What—remind me, what were you doing this whole time?

LULU: [laughs] I was rearing a small baby.

LATIF: Right.

LULU: Yeah, I was on maternity leave.

LATIF: Okay, so creating life. That sounds like that's—yeah ...

LULU: I was learning to juggle, because now—now there's three, so you gotta always have one in the air.

LATIF: But you were also, as I was to learn, scheming.

LULU: Scheming.

LATIF: For new episodes.

LULU: I came back—on day three—I actually looked back. It was day three, because I had gotten wind of a beautiful but terrifying and arguably kind of urgent story.

LATIF: Hmm.

LULU: And so I dragged you into the studio, totally unprepared.

LATIF: That's true.

LULU: To meet with one of our favorite Radiolab guests ...

CARL ZIMMER: Hi, guys.

LATIF: Hey!

LULU: ... Carl Zimmer.

LULU: Your ears must have been burning right then.

CARL ZIMMER: What have—what have people been saying about me now?

LULU: Carl Zimmer, the sort of the prima ballerina of science writing.

LATIF: The best. The best.

CARL ZIMMER: That's great. Thank you so much.

LULU: He is a columnist for the New York Times. He's written all these gorgeous science books. And he has been working on a new story that is all on your turf; it is history of medicine.

LATIF: Wow!

LULU: And I do not think you know it.

LATIF: Really?

LULU: And it begins with a man named Fred Meyer.

CARL ZIMMER: So you probably have never heard of Fred Meyer.

LATIF: No. Never.

CARL ZIMMER: So Fred Meyer, he started out as what he described as a "watermelon doctor."

LATIF: Okay.

LULU: This was in 1915, by the way.

CARL ZIMMER: So he—he was a plant pathologist, and he was actually in college, like, working one summer down in Washington, DC, and he noticed this huge pile of rotten watermelons next to a boxcar.

LULU: And when he cracked them open, he noticed they weren't rotting in, like, the normal way. They were weirdly black and crazily slimy.

CARL ZIMMER: And, you know, this is the kind of thing he studies. So he takes some of the watermelons in his arms back to the lab, and he actually discovers a fungus that is killing them.

LATIF: Hmm.

CARL ZIMMER: And this is actually new—new to science. So, like—so he discovers his own disease. He's, like, 18 or 19.

LATIF: Wow!

CARL ZIMMER: And so then he starts to, like, think about, well, how does this fungus get from one watermelon to another?

LULU: So he starts looking for this disease out on watermelon farms in the fields, and he starts noticing that it can jump from one watermelon to another, even if they aren't next to each other. So pretty quick, he realizes ...

CARL ZIMMER: This fungus goes through the air. It sends up spores that travel around to get to new fruit.

LULU: Now at the time, every scientist—and honestly, every four year old—knew that things like dandelion seeds and pollen can float through the air. But the idea that living things could travel through the air and stay alive long enough to infect plants and make them sick? That was totally new to Meyer. So he started to wonder, like, how far can these things travel?

CARL ZIMMER: Like, how high do they go?

LULU: You mean, how high, like, up into the air?

CARL ZIMMER: Yes.

LATIF: Huh.

CARL ZIMMER: So he builds these, like, really crazy, crude devices. Basically sticks, like, a petri dish onto a stick. And he starts getting in airplanes.

LULU: This is the early 1930s, so we're talking little propeller planes, you know, with the pilot seat open to the air.

CARL ZIMMER: And he gets into these, you know, open cockpits.

LULU: With his little petri dishes on a stick.

CARL ZIMMER: And he's just hanging them out in the air, you know, in these biplanes.

LATIF: Wow!

CARL ZIMMER: You know, people think he's crazy. You know, he goes on blimps, and he's sticking these things out from the gunwale of blimps and the blimp crew are, like, "What are you doing?"

LULU: [laughs]

CARL ZIMMER: But he's catching stuff.

LULU: He catches microbes that usually live down on the earth on potatoes and lettuce and celery, another that ferments cheese, another that was known to kill trees—all floating around thousands of feet up in the air.

CARL ZIMMER: Then he finds out that Charles Lindburgh and his wife Anne are gonna be flying across the Atlantic.

LATIF: Hmm.

CARL ZIMMER: Charles Lindburgh designs a special instrument to hold out of his plane to catch things—and he does.

LATIF: Wow!

CARL ZIMMER: Over Greenland, over the Atlantic, he's catching all sorts of stuff.

LULU: He attaches his device to balloons that are being sent up into the stratosphere.

CARL ZIMMER: And 12 miles up he catches stuff.

LULU: All these invisible, tiny little creatures, floating around alive, in the air around us, but also miles up into the atmosphere. And eventually, because of all this stuff he's finding ...

CARL ZIMMER: He's actually able to persuade the government, the US government, that they should basically, like, open up a bureau for this life in the air.

LULU: And he actually coins a term for this whole field.

CARL ZIMMER: He calls it aerobiology.

LATIF: Hmm.

CARL ZIMMER: Which no one's heard of before. But just like the government is supporting a weather service, he wants to basically have an aerobiology service.

LATIF: Like, it would be, like, "These bugs are in the air today. Like, watch out for the ..." Is it that kind of thing?

LULU: [laughs]

CARL ZIMMER: That would be one thing he was ultimately hoping for, yeah.

LATIF: Huh.

CARL ZIMMER: And the government agreed to this.

LATIF: Wow!

CARL ZIMMER: In 1938 they were like, "Yes, go for it." So for his first big expedition for this grand new project, which he's now finally getting paid for, he gets on one of the first commercial flights that's going across the Pacific.

LATIF: All right.

CARL ZIMMER: He's very excited. He gets on—onboard the plane that's supposed to get to Manilla. It never gets there. There's a huge search. The US Navy just goes scouring the Pacific for days. This is all on the news. No one ever found the plane. So he disappears, and basically this brave new science of aerobiology kind of disappears with him.

LATIF: Wow!

CARL ZIMMER: In less than a year after he coined the name "aerobiology."

LULU: The freaking founder of aerobiology disappears into thin air?

CARL ZIMMER: Yeah. And in some ways it seems almost cursed.

LULU: So this is why I wanted to talk to Carl, because he actually just wrote a book.

LULU: Can you describe the cover?

CARL ZIMMER: Yes. It's got a groovy yet sinister rainbow cloud on it.

LULU: It's totally groovy yet sinister.

LULU: The book is called Airborne, and it's all about this whole other layer of life that lives up there in the air.

CARL ZIMMER: This is the story of this amazing science that has been trying to get off the ground for centuries.

LULU: A field that, despite a trail of other scientists like Meyer who saw with clear evidence how alive and sometimes dangerous the air could be, it just wasn't able to break through—until—well, until a moment in very recent history when millions of lives were on the line.

CARL ZIMMER: That's—yeah. And I just was trying to—trying to wrap my arms around it with this book.

LULU: And what Carl found was this eerie history of ideas—ideas that were wrong for the right reasons and right for the wrong reasons, and a terrible and complicated truth somewhere in the middle.

CARL ZIMMER: Yeah. And it's—it's a long, crazy story.

LATIF: We're here for it. We've got some popcorn.

LULU: How far back do we go?

CARL ZIMMER: I think we do have to go back, you know, 2,500 years ...

LULU: All right.

LATIF: Okay.

CARL ZIMMER: ... to Hippocrates.

LULU: Okay, so we're in Greece. This is a couple hundred BC. And Hippocrates, in addition to being, you know, do-no-harm, Hippocratic oath guy, was supposedly one of the first to argue that diseases might not be coming from angry gods trying to punish you, but rather from nature itself.

CARL ZIMMER: Hippocrates developed a really powerful concept, that if you look at these different diseases that people got, they got them because they breathed in bad air. Hippocrates would refer to it as a "miasma."

LATIF: Hmm.

LULU: What is, like, the Cliffs Notes of how he saw them? Are they just, like, bad vibes?

LATIF: Smoke monster?

LULU: Ghosts?

LATIF: Yeah.

CARL ZIMMER: It was a—a corruption. Think of it as a corruption of the air. So corrupt air, you know, might smell bad. You know, marsh water could give off fumes, or even a rotting corpse. Or the alignment of planets might also somehow disturb the air.

LULU: And while that may seem silly to us now, it was a very useful idea.

CARL ZIMMER: It seemed to work, and so classical medicine really just sort of took up miasmas just as a fact.

LULU: And it's not a bad idea. I mean, you get it. Like, you see a whole town at the same moment getting a thing.

LATIF: I live in LA right now, post-wildfire. Everyone is afraid of, like, random bits of ash or asbestos or lead or whatever just randomly in the air. And I get how miasmas could really feel real because right now they kinda do.

CARL ZIMMER: Right. So in a way, that kind of stretchiness of the miasma idea helped it to just last a really long time.

LULU: And which kind of diseases did—did this account for?

CARL ZIMMER: It seems like everything. I mean, it's just a long, long list of diseases that Hippocrates and then later people would ascribe to miasmas.

LATIF: Wasn't, like, malaria—it's like, "bad-air-ia?" Like, it's from bad air, right?

CARL ZIMMER: Right. Right. So malaria got its name in the Renaissance, I believe. In Italy. This was an idea that in various forms really, like, took hold, and it worked.

LULU: And this was the central belief for what caused disease for about 2,000 years. Then comes the Enlightenment, and you've got all kinds of new ways to investigate the world and think about what counts as evidence, and great new ways of literally seeing the world.

CARL ZIMMER: So in the 1600s, people are inventing the first microscopes. And they're looking through the microscopes, and they're seeing all these tiny little things squirming around—these animalcules, these germs. And this starts to give some people the idea that hey, like, these might be things that make people sick.

LULU: Basically this is the birth of germ theory. But at the time, the "bad air" people thought this was ridiculous.

CARL ZIMMER: "This is just dreaming. You are just letting your imagination run wild. Where is your actual proof? You're seeing these things through a microscope, then there are these people dying of the plague. You haven't shown us that any bacteria are causing that plague." And so authorities just brushed away the germ theory of disease decade after decade after decade.

LULU: So this debate of, "Hey, I think it's in the germs." "No, it's in the air." "I think it's in the germs." "No, it's in the air," it goes on and on and on, with the germ theory people building up more and more evidence, and the air people, the miasma people just shouting them down, until the late 1800s.

CARL ZIMMER: In the city of Hamburg in 1892, there was an outbreak of cholera.

LULU: You know, terrible. People turning blue in the face, collapsing in the streets, dying by the thousands.

CARL ZIMMER: And all the medical authorities in Hamburg, they were all big believers in miasma. So it's 1892, and people in charge are still treating this like a miasma. And there was this leading figure in terms of public health named Max von Pettenkofer. He was incredibly famous, and everyone took his opinions incredibly seriously.

LULU: And his view was that cholera was caused by fumes coming out of the ground.

CARL ZIMMER: And so you just needed to make sure that the ground was clean, and then these fumes wouldn't come into people's houses and give them cholera.

LULU: Meaning, like, clean of garbage?

CARL ZIMMER: Yeah, garbage, waste.

LULU: Yeah.

CARL ZIMMER: And so people were saying, "Hey, this is what von Pettenkofer says," and everyone followed what he said.

LULU: Now on the other side, you've got this German doctor named Robert Koch. He was a germ theorist, and his argument was that no, cholera was not in the air, it was a bacteria moving through the water that people were drinking. But Pettenkofer ...

CARL ZIMMER: He kept resisting it, saying, "No, it's—cholera's not spread through the water." He just refused to believe it. Like, "No, no, no. It's not the water, it's not the water. No."

LULU: Spoiler alert: It was the water. But Pettenkofer was so sure of himself ...

CARL ZIMMER: He actually asked Robert Koch for some of the cholera bacteria from Hamburg. And he had it prepared in a tube, and he had a bunch of his followers in front of him and he drank it.

LATIF: Oh, wow!

LULU: That was the strength of his conviction of, "No, this is miasma, this is the air. I will drink cholera soup."

CARL ZIMMER: Yes. Yeah. There's this amazing line he wrote later. He said, "Even if I had deceived myself and the experiment endangered my life, I should face death calmly, for it would not be as a thoughtless and cowardly suicide. I should die in the cause of science like a soldier on the field of honor."

LATIF: Wow!

LULU: Wow!

CARL ZIMMER: And well, he survived and he talked about it later.

LATIF: He survived?

LULU: Like, how did he survive that?

CARL ZIMMER: Well—so I mean, the awkward fact is that a lot of people who get infected with cholera don't get that sick.

LATIF: Hmm.

CARL ZIMMER: And it turns out that Robert Koch's colleagues who gave him the bacteria kind of had an idea of what he was gonna do. And so they actually—they actually took their sample from a patient who had had a very mild case.

LULU: Oh, because they didn't want him to die.

CARL ZIMMER: That's what they said later.

LATIF: That's so nice of them!

CARL ZIMMER: Yes. But he didn't know it, so after he recovered, he wrote a note to Robert Koch. He said, "Herr Doctor Pettenkofer has now drunk the entire contents, and is happy to inform Herr Doctor Professor Koch that he remains in good health." So I think that was a little kind of "screw you" moment.

LATIF: Yeah.

CARL ZIMMER: But with this terrible outbreak in Hamburg ...

LULU: Once Robert Koch comes on the scene with his germ theory ideas ...

CARL ZIMMER: He supplies clean water to people. He has buildings cleaned out. And they stop the cholera outbreak.

LATIF: Wow!

LULU: It was a clear message that this disease did not come through the air. It did not travel in the air. It was a bacteria in the water.

CARL ZIMMER: And, you know, Robert Koch says, "Okay, Germany as a whole needs to deal with diseases like this from now on this way."

LATIF: Hmm.

CARL ZIMMER: "We're done with miasmas. It's all germ theory now." When the germ theory of disease won out, all these different diseases that had been thought to be spread through the air just by miasmas turned out to have nothing to do with that. So malaria, you mentioned. That's not bad air. That's mosquitoes. Ringworm ...

LULU: Not spread by fumes, but instead ...

CARL ZIMMER: By ordinary skin contact. Syphilis ...

LULU: Not caused by corrupt air, but ...

CARL ZIMMER: By a kind of bacteria transmitted only by sex. Vibrio and salmonella ...

LULU: Came from contaminated meat or water.

CARL ZIMMER: The rabies virus required the service of live animals which bit their victims. Jail fever proved to be caused not by prison air but by lice-borne bacteria. Rats carried fleas infected with Yersinia pestis.

LULU: And that, not the air, is how people got the plague.

CARL ZIMMER: And so you just had this whole long list of diseases where microbiologists in the late 1800s would definitively prove ...

LULU: Were caused by germs, not the air.

CARL ZIMMER: It didn't seem to them like there was anything left for the air. I mean, you literally have these public health authorities at the time saying things like, "A patient's breath is free of germs." Just flat out. Forget the air.

LULU: And that basically became medical dogma for the next century. But here is what I love about Carl's book is that he finds this whole mostly forgotten history, this trail of scientists who are piling up evidence that okay yeah, germs can cause disease but also germs can travel through the air.

CARL ZIMMER: Laying out very clearly that people can potentially get each other sick with all sorts of diseases through the air over long distance.

LULU: So in the early 1900s, you've got our watermelon guy, Fred Meyer, doing his thing with plant diseases. But then there are these other stories of other scientists who were taking that idea and extending it to human disease. And many of them, like Meyer disappearing over the ocean, would end up being mostly forgotten.

CARL ZIMMER: So you do not know who William and Mildred Wells are?

LATIF: No.

CARL ZIMMER: So ...

LULU: So around the time that Meyer is flying around with Lindburgh, this married scientific duo, William and Mildred Wells ...

CARL ZIMMER: Take a cream separator, something you'd separate cream from milk ...

LATIF: Yeah?

LULU: And they figure out a way to kind of MacGyver it into a device ...

CARL ZIMMER: Glass cylinder called the Wells Air Centrifuge.

LULU: ... that would spin around, and in so doing separate out and capture bacteria and viruses in the air.

CARL ZIMMER: Yeah. And ...

LULU: And then they go on—or at least William goes on to, like, show this in animals, too, right? To show transmission, airborne transmission.

CARL ZIMMER: Yeah. Yeah, so William gets busy in his lab building something that the newspapers call "the infection machine."

LULU: [laughs]

CARL ZIMMER: Basically, what he does is he has a chamber, kind of a big bell jar. And he can put animals in there, he can put mice in there, he can put a rabbit in there, and he can create these mists of disease—influenza or tuberculosis. And he's able to show that these animals, just inhaling the stuff, get sick.

LULU: Now even at the time, scientists knew that diseases could be carried by a cough or whatever, you know, travel maybe five, six feet. But the Wells's were discovering something very different from that.

CARL ZIMMER: These were not, you know, big droplets that were, you know, shot out of someone's mouth when they sneezed and then just dropped to the ground. These were droplets that had to float—aerosols, sometimes people call them.

LULU: Which could travel and cause disease over much, much larger distances.

CARL ZIMMER: And so the—demonstrating that these things could get so far was—that was quite something.

LULU: Which, like, feels like that should be revolutionary in that moment. Like, that feels like it should be massive, scary, big, important news for public health, for a lot of people.

CARL ZIMMER: You know, a lot of other scientists and doctors were very skeptical. It doesn't help that ...

LULU: Why—why is everyone still so confident germs don't go through the air?

CARL ZIMMER: It's—it's—I think it's one of the hardest things to figure out, like, why people don't recognize something that's just out there. And, you know, I would—you know, let me put it this way. The Wells's enemies were not stupid.

LATIF: Hmm.

CARL ZIMMER: They just would look at the evidence differently. They would have different kinds of thresholds for what would convince them, what—you know, what is gonna make them step away from just, you know, generations of what people are taught in medical school.

LULU: And also, Carl says, I mean, just think about the practical public health side, the implications of this if this were true, the idea that disease is just everywhere in the air, is very daunting.

CARL ZIMMER: You know, a lot of the guidelines for staying healthy, they're very individual-based. Here's what you as an individual should do.

LATIF: Right.

CARL ZIMMER: Just stay a few feet away from people who look sick. If you have a cough, cover your mouth. But, you know, if it's all in the air around us ...

LULU: Yeah.

LATIF: Yeah.

CARL ZIMMER: ... you know, you have to think differently.

LULU: So the findings about the air that Wells and this trail of other scientists were seeing through the '30s and '40s and '50s, they just never quite took hold.

CARL ZIMMER: It was all hidden knowledge. I mean, these people were almost entirely forgotten.

[ARCHIVE CLIP: [singing] "Oh Fortuna."]

LULU: And then some 70 years later, we would all go through the painful process of finally thinking differently, thanks in part to a song. That's coming up after this break.

LATIF: All right. Okay, here we are. Latif.

LULU: Lulu.

LATIF: Radiolab.

LULU: We're back with Carl Zimmer ...

CARL ZIMMER: Yes.

LULU: ... who started us way back over 2,000 years ago, but is about to bring us up to the very recent past.

CARL ZIMMER: Yeah, so on March 10, 2020 ...

LULU: A group of about 60 people ...

CARL ZIMMER: ... come into this church on the outskirts of Skagit Valley in Washington. They set up chairs. Somebody closes the door. The heater is running for a while and then it shuts off. And they start to sing.

[ARCHIVE CLIP, Skagit Valley Chorale: [singing]]

LULU: This group is called the Skagit Valley Chorale, and this is one of their rehearsals. Now the people in this chorus, many of whom were retired, they knew about the sort of early spread of COVID.

CARL ZIMMER: There are starting to be reports of it in Washington State, so they did take precautions.

LULU: People who had symptoms like sneezing or coughing stayed home. Those that came kept their distance from one another as much as they could. They sanitized surfaces in the room, they washed their hands. So they were following all of the CDC guidelines at the time.

CARL ZIMMER: And they all thought, "We're doing what the Centers for Disease Control have been telling us to do, so we should be okay." But a couple of days later, some of them started to feel terrible.

LULU: Most of the 60 people in the room that day got sick.

CARL ZIMMER: Just boom, just in that one rehearsal. And a couple—three people ended up in the hospital and two of them died.

LULU: And soon it was all over the news as one of the earliest really big spreading events.

CARL ZIMMER: This little singing group in a corner of Washington State suddenly became internationally famous.

LULU: But for the people who were there that day ...

CARL ZIMMER: They said, "How can this be happening? We did everything we were supposed to. It's not like we were all, you know, hugging each other, and we weren't sneezing on each other. We were just singing."

LULU: Yeah.

CARL ZIMMER: And people who were 40 feet away from each other were getting sick.

LULU: But that feeling of disconnect, says Carl, was actually a symptom of the way experts and public health officials were thinking about COVID in those first few months.

CARL ZIMMER: In March, 2020, when these singers got sick, you actually had public health authorities saying explicitly COVID is not airborne.

LULU: The focus was on staying home if you were sick, you know, wiping down surfaces, washing your hands.

CARL ZIMMER: And that is all really based on this idea that a disease like the flu is spread in big droplets that, you know, you wipe your—you wipe your mouth or your nose, you smear it on a doorknob, or maybe you cough and you, like, cough right in someone's face. And so that was—that was it. And, you know, I as a reporter was trying to make sense of this disease, like we all were. Did you wipe down your groceries?

LULU: Yeah.

LATIF: Totally.

CARL ZIMMER: Me too. And, you know, I would—I would tell people, like, "Yeah, wash your hands. Wash your hands." And I even went on Radiolab and said, "You should all wash your hands because that's one of the great classic ways to stop the spread of infection." And that's true.

LATIF: I helped produce that episode. I still stand by that episode. That was great.

CARL ZIMMER: Yeah, you definitely still wash your hands, but you can't assume that washing your hands will keep you safe from an entirely new virus. And we had to learn the hard way. And I mean, you know, I can—I can remember actually going to have dinner with friends and, you know, I just said, "I'm not gonna hug you, I'm not gonna shake your hand." You know, I was trying to be, you know, good and careful.

LULU: And—and any mask on?

CARL ZIMMER: Of course not.

LULU: Right. Yeah.

CARL ZIMMER: It was ridiculous in hindsight.

LULU: Yeah.

CARL ZIMMER: Yeah, we sat down, you know, after putting on this big show of not making contact. And we'd sit down and we'd talk. Like, knowing what I know now, I think, "Wow, I was endangering my friends' lives." If you're sitting indoors across a dinner table, and having a long, lively conversation, and if you have COVID, they could get COVID, too.

LATIF: Yeah.

CARL ZIMMER: You don't have to sneeze on them. You don't have to drink from the same glass. You just talk. Or sing. Or breathe.

LATIF: Right.

LULU: Now, of course, by spring 2020, there were scientists arguing that COVID had to be airborne, you know, that it could travel further than just droplets from a sneeze or a cough. But it took a really long time for that idea to be accepted.

CARL ZIMMER: And it wasn't just taking a long time. People were yelling at each other. And the World Health Organization was saying, "Cut it out. You know, COVID is not airborne." Like, everything was very strong, opposite poles. And I just thought, what is going on? Like, why is it so hard? And I didn't appreciate just, you know, all the history behind this.

LULU: And now that he does, Carl blames miasmas in a way, or the fact that germ theory was born largely in opposition to the idea that the air could carry sickness. Once that idea had been debunked, it took its place alongside spontaneous generation, or the idea that the Earth was flat as foolish ideas that science had debunked, which made it really hard for the occasional bits of evidence that there was life in the air to break through.

CARL ZIMMER: You know, I would talk to people who—you know, I talked to Anthony Fauci. I said, "What happened?" And he's like, "Well look, you know, you just have to understand, like, this is what we were taught in medical school. This is what we were all taught. We just didn't take airborne infection seriously" You know, he learned a hard lesson in COVID and he admits that.

LULU: And interestingly, one of the things that finally brought medical health professionals around was what happened at the Skagit Valley Chorale.

CARL ZIMMER: Yeah, so there were a few scientists who said, "Folks, this might be airborne." And one of—one of the things that they did was that they got in touch with the Skagit Valley Chorale, because it looked from the news reports like this might be a classic case of airborne transmission. And so they actually collaborated with the singers. And they tried to reconstruct what had happened and, you know, how—how was the air moving that night in the church? So some of these scientists published a paper on this case, and it turned out to be some of the most compelling evidence that COVID can be airborne.

LULU: Wow! I never knew that—that second act of the story.

LATIF: It feels like the story you're telling, it's like a story of two orthodoxies, two ways to explain how and why we get sick that are both kind of right.

LULU: Hmm.

CARL ZIMMER: You know, the idea of miasma was in a lot of ways, really, really wrong. [laughs] And a lot of people may have died because of it. And the germ theory is, in many ways really, really right, and a lot of people's lives have been saved. But it does seem like in that swinging away from the old ideas, people started to jump to conclusions that maybe went too far.

LULU: Or at least left us all with a blind spot.

CARL ZIMMER: I mean, sometimes I imagine, like, if we had glasses where we could see, like, living things in the air ...

LULU: Yeah.

CARL ZIMMER: ... we might think differently. So we've been talking a lot about, you know, living things coming out of our noses and our mouths.

LATIF: Yeah.

CARL ZIMMER: But, you know, things get into the air in all sorts of ways. Like, if you go to the beach and you're looking at the waves, like, every time those waves crash, they send up tiny bubbles of seawater, some of which have bacteria and algae. So if you're walking along the beach, you would see just these plumes of living things, like, rising up, blowing onto land, or going up higher into the sky. If you take a walk in the woods, you would see all this stuff streaming out of the soil. You would actually see lots of bacteria and fungi and things actually coming off of the leaves on the trees. You know, there would be all this stuff that you would recognize as being constantly, like, pumped up into the air all the time from everywhere.

LULU: Are there things that, like, play out their whole life up there? Are there dramas and worlds and existences up there in the aerobiome?

CARL ZIMMER: Well, so, you know, there are lots of bacteria in the clouds, okay? And they're actually possibly eating the clouds.

LATIF: What? [laughs]

LULU: What?

CARL ZIMMER: They are eating the clouds. There's organic matter in the clouds, and it's possible that bacteria can find just enough of that stuff to swallow up, to grow very, very slowly, but to grow and maybe even to divide, in the clouds.

LATIF: Weird!

CARL ZIMMER: And, you know, when it rains, it's not just raining water. It's raining lots of bacteria as well.

LULU: How far has—like, how far has something been seen to travel, in terms of a germ or a bacteria or something that could cause human illness?

CARL ZIMMER: There is a—there is a terrible disease called Kawasaki disease that affects children, a really harsh disease with kids. They have very—very strong immune reactions. Their—their tongue, you know, turns the color of strawberries. And kids will get terrible heart damage from this disease, Kawasaki disease, and that may kill them later. Nobody has found the germ that causes Kawasaki disease. It seems like it's caused by some kind of germ, but no one has found it yet.

LULU: Hmm.

CARL ZIMMER: But what they have found is that in Japan, flare ups of Kawasaki disease seem to correlate with strong winds and dust coming from China.

LULU: Whoa!

CARL ZIMMER: And we get Kawasaki disease in the—in the West Coast of the United States, and those cases seem to correlate with the weather patterns going across the Pacific.

LULU: Oh my God, with a wind current coming all the way from China?

CARL ZIMMER: All the way from China, maybe.

LULU: Yeah.

CARL ZIMMER: Maybe—maybe there's some fungus or some other living thing that gets kicked up with the dust in China and then gets picked up by the wind and then just keeps going.

LULU: Thousands of miles, all the way across the ocean, still alive enough to—maybe.

CARL ZIMMER: Yeah. Still capable of killing a child.

LULU: Oh my God.

CARL ZIMMER: You'll see sometimes these amazing maps of the world's weather, you know, seeing, you know, clouds moving along, and low pressure and high pressure systems and so on across the whole planet.

LULU: Mm-hmm.

CARL ZIMMER: Aerobiologists would like to do that for life.

LULU: Hmm.

CARL ZIMMER: They would like to create a global map in motion, showing how living things are moving around the world in the air. That is a dream that they are working on.

LULU: I guess my—I have one, like, big last question for you, Carl. This concept of the aerobiome and a world up there in the clouds, or up high, I mean, what else could be in there? Can you just kind of give us the profile? Like, you know, we've got aquatic worlds and earth world and, like, what else is up there?

CARL ZIMMER: I think that there is a lot of life up there that we just don't know about yet.

LULU: Hmm.

CARL ZIMMER: Even in the microbial world, when microbiologists, like, are capturing microbes in the air, they tend to find totally new species. These are species they just didn't know about. And so, you know, with viruses and bacteria, fungi, there's just a huge diversity of things up there that we don't know about.

LULU: Young scientists wanting to make a name for yourself, go to the air.

CARL ZIMMER: Totally go. Absolutely. Absolutely. Go to the air, yeah. And I don't want people to, like, leave the book saying, like, "Okay, that's it. I'm never breathing again." We probably actually get some benefit from breathing the aerobiome. It just—you know, you just want to be breathing in the living things in, say, like, forests, for example. And, you know, our immune systems might actually be primed to have kind of a partnership with these things that we breathe. I mean, some of them, we breathe it in and it ends up in our lungs or in our gut and just stays there. Like, we breathe in stuff and some of it just stays. And maybe these are partners that we need.

LATIF: Thank you, Lulu, for dragging me into that interview. It was a real breath of fresh air. I feel like you actually can't say that on public radio.

LULU: No, it's Terry Gross's domain.

LATIF: Right. Right.

LULU: Well yes, thank you for joining me on the conversation. And for everyone listening, Carl's book is called Airborne: The Hidden History of the Life We Breathe. And it is truly—it's so beautiful. It is full of so many more stories you didn't know, and really gorgeous writing around the Chorus, around all kinds of stuff with COVID, his own lack of understanding and learning, and it's just—it's gorgeous. Airborne. Go check it out.

LATIF: Even though it doesn't have wings, it's floating to a bookstore near you. This episode was reported—honestly, it was reported by just Carl Zimmer.

LULU: Yeah.

LATIF: And his book. But it was reported and produced by Sarah Qari, and fact-checking by Natalie Middleton.

LULU: Thanks so much for listening. See you next week.

LATIF: Bye!

[LISTENER: Hi, I'm Rachel and I'm from Norrkoping, Sweden. And here are the staff credits. Radiolab was created by Jad Abumrad and is edited by Soren Wheeler. Lulu Miller and Latif Nasser are our co-hosts. Dylan Keefe is our director of sound design. Our staff includes: Simon Adler, Jeremy Bloom, Becca Bressler, W. Harry Fortuna, David Gebel, Maria Paz Gutiérrez, Sindhu Gnanasambandan, Matt Kielty, Annie McEwen, Alex Neason, Sarah Qari, Sarah Sandbach, Anisa Vietze, Arianne Wack, Pat Walters and Molly Webster. Our fact-checkers are Diane Kelly, Emily Krieger and Natalie Middleton.]

[LISTENER: Hi, this is Charlie Lou, calling from El Pescadero, Mexico. Leadership support for Radiolab's science programming is provided by the Gordon and Betty Moore Foundation, Science Sandbox, a Simons Foundation initiative, and the John Templeton Foundation. Foundational support for Radiolab was provided by the Alfred P. Sloan Foundation.]

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