LULU MILLER: Hello. I'm Lulu Miller. If you joined us last week, you met the hidden body part stowing away inside your body. And today, we have another hidden story about life and non-life and how the line in between them is way blurrier than we might think. We are talking about viruses today. This episode is a rewind, but it's a lovely one. It's called "Shrink."

LULU: And what I love about it is not just that it busts a binary between life and non-life that I always thought was hard and fast, but also that as you listen, it really feels—at least to me—like Robert Krulwich and Jad Abumrad, OG hosts, that they kinda shrink down into these little boys who are so giddy with questions for Carl Zimmer. It's like they're—I picture them like two little boys at Santa's knee just taking in the knowledge. And it's a really raw, lovely glimpse, I think, of what this show does best when it does its best, which is to make space for questions and for real listening. So I hope you enjoy this kind of giddy romp through the evolution of life and non-life and all the places where that line blurs out a bit. Here we go!

[RADIOLAB INTRO]

CARL ZIMMER: Come on! Totally, like, you guys keep saying we want to talk to you about three things.

ROBERT KRULWICH: Radio jocks.

JAD ABUMRAD: Okay, let's do—let's do this.

JAD: Hey, this is Radiolab. I'm Jad Abumrad. We're gonna do something that's a little bit unorthodox today—at least for us. You know, if you've listened to the show in the last 10 years or so, however long we've been doing this, you understand that, like, we like to edit, right? We like—we like a good edit—or 70. But today I want to play you something that has almost no edits at all. It's just a conversation, which is, of course, the foundation of what we do. These long, rambling, occasionally profane, error-strewn conversations that we then edit into something coherent.

JAD: But today, I want to show you the messiness. No edits! This is a chunk of a conversation with science writer Carl Zimmer. He came and sat down with us a while back, and we talked for four hours. Two of those hours became the basis for the CRISPR podcast that was a few podcasts ago that was about gene editing. But then we kept on going for another two hours, and he told us this story—actually, two stories but we're only gonna play one—that I thought was really cool. And it's about this new way of looking at life.

JAD: Is this a longform story, a medium story or a short story?

CARL ZIMMER: No, it's not a—we can get through this a lot faster than CRISPR.

JAD: Okay.

ROBERT: Okay.

JAD: I really like CRISPR, by the way.

ROBERT: So do I.

JAD: I'm into it.

CARL ZIMMER: CRISPR is—yeah, it's the bomb. [laughs]

JAD: [laughs]

ROBERT: [laughs] Yeah, a perfect way to describe it.

JAD: [laughs]

CARL ZIMMER: A biological bomb.

JAD: Okay, so chapter two.

ROBERT: Okay, maybe you could start the story. Once upon a time ...

CARL ZIMMER: Sure. So once upon a time being, I'd say—once upon a time being before 2003 ...

ROBERT: Mm-hmm.

JAD: Okay.

CARL ZIMMER: ... we basically had two kinds of living things on Earth. We had cellular life and we had viruses, and it was nice and distinct and clear cut. And so cells included us, because our bodies are made of cells, and bacteria, which are single-celled, and all the other things that can grow and let their cells divide. They have DNA, they have proteins in them, they all have that stuff.

CARL ZIMMER: And then over here, you had viruses. And viruses were just little packages of genetic material that would go from cell to cell and use the cell to make new viruses. And so inside of them, all they had were genes and a couple proteins that would then sort of hijack their host.

ROBERT: I mean, they seem, like, so—so preliminary that they don't even maybe not even qualify as life.

CARL ZIMMER: Right. They can't grow on their own. They can't generate their own energy, so us and all other cellular life, we—we make a kind of a fuel called ATP. And we need that to do every little thing in our body. And viruses don't make ATP so, you know, they're ...

ROBERT: So couldn't we say that life is us—cells and multicellular beings—and then there's a sort of pseudo-life?

CARL ZIMMER: Yeah.

ROBERT: Which is these little things that live off of us.

CARL ZIMMER: Yeah. Yeah, a lot of people—a lot of scientists don't really think viruses are truly alive. They just sort of take advantage of life to—to make more copies of themselves.

ROBERT: Okay.

JAD: Can I ask a dumb question? So viruses, they don't have a wall around them in the way that cells are walls, essentially? Are walled-off areas?

CARL ZIMMER: They might have a protein shell.

JAD: Uh-huh.

CARL ZIMMER: And—and so, you know, when the flu virus goes into a cell, that protein shell kind of breaks open and the genes and proteins inside come out.

JAD: They do have containers that contain them for ...

CARL ZIMMER: Yeah.

JAD: ... for a while. I see.

CARL ZIMMER: Mm-hmm.

JAD: Isn't that one of the—somebody who had a list of rules that make you alive, and wasn't a container was one of those rules?

ROBERT: I—I—yeah.

CARL ZIMMER: Yeah, that ...

JAD: But I mean, they don't do the energy, but they have the container at least.

CARL ZIMMER: Right. So the problem with viruses is they have some of the things that we think are essential for life, but not quite all of them.

JAD: Right.

CARL ZIMMER: So it's been convenient to just say viruses are not alive.

JAD: Mm-hmm.

CARL ZIMMER: Put them over there because they don't have everything that cellular life has, so we'll just say they're not alive.

JAD: Okay.

CARL ZIMMER: They're just viruses.

JAD: Gotcha.

ROBERT: And then?

CARL ZIMMER: So then what happened is that there was a scientist named Timothy Rowbotham in England who was investigating a ...

ROBERT: Timothy Rowbotham?

CARL ZIMMER: Timothy Rowbotham.

JAD: Yes.

ROBERT: That's a good English name.

JAD: Rowbotham? With a "th—"?

CARL ZIMMER: Timothy Rowbotham was—was working in Bradford, a city in England, and he was looking at the kinds of bacteria that might be growing in a hospital.

JAD: Hmm.

CARL ZIMMER: You know, like, they were having some problems with pneumonia outbreaks and so on, and he was like, "Okay, what's growing around here?" And so he went to a—sort of a cooling tower for water on top of the hospital, and he took a sample and he went and put it under his microscope and he was like, "Hmm, there's some interesting bacteria here. Oh, here's a very interesting bacteria that doesn't really look like anything I've seen before."

ROBERT: Wait, and this guy would just kind of crawl around to weird places and just snatch little snippets of scum? Or what would he ...

CARL ZIMMER: Yeah. I mean ...

ROBERT: What was he? What was his job?

CARL ZIMMER: He's a microbiologist.

ROBERT: Oh. Of course.

CARL ZIMMER: So, you know, it would be good to know. Like, I mean ...

ROBERT: Is that what microbiologists do? They just go scrape little bits of rock or—or water tower scum?

CARL ZIMMER: They search the world—yeah, I mean microbes are everywhere, so microbiologists go everywhere to find microbes. So they even, you know, in a water tower on a hospital.

JAD: Was he—was he in a kind of an investigatory role? He was trying to help them—help them figure out which bacteria are making people sick?

CARL ZIMMER: That was one of the hopes.

JAD: Mm-hmm.

CARL ZIMMER: But, you know, he was thinking of doing a survey because, you know, there are diseases like Legionnaires' disease, which can, you know, grow in these sort of containers of water. You know, that's—there's some concern about that. So better to get to know what's growing.

JAD: Mm-hmm.

CARL ZIMMER: So he's particularly taken by one thing that he assumes is bacteria, and it's got a kind of interesting kind of roundish shape, and he call—and when bacteria are round, you can call them cocci or coccus. So he names this Bradford coccus. He gives it a name.

JAD: That's where the coccus name comes from? It's referring to the shape?

CARL ZIMMER: Mm-hmm.

JAD: Like, streptococcus?

CARL ZIMMER: Mm-hmm.

JAD: Is it because it's round?

CARL ZIMMER: Mm-hmm.

JAD: I did not know that. The things you learn when you talk to Carl Zimmer.

ROBERT: The things you learn.

JAD: My God! Okay.

CARL ZIMMER: So—so he's trying to study this thing, and he's trying to—so when you're a microbiologist, the way you study bacteria is you get them to grow. And he can't get this to grow. He's feeding it things and it's like, it's not growing. Why is it not growing? I can't figure it out. And eventually, you know, he just hits a wall, and unfortunately his lab got shut down, and so he basically said, "Okay, I don't want to throw this stuff out, so I'm gonna—I'm gonna give it to some of my colleagues in France."

JAD: It wasn't dying, it just wasn't growing?

CARL ZIMMER: Yeah. So he gave it to a scientist named Bernard La Scola and his colleagues, and they kind of put it ...

ROBERT: Bernard La Scola.

CARL ZIMMER: Ah, oui. And he just sets—he just sets it aside for a while and doesn't—you know, it's just more bacteria, you know? And it's—for some reason, he decided to, you know, take a look at this Bradford coccus. You know, like, what was this thing that Rowbotham was talking about? So he looks at it and he says, "Okay, this is the size of bacteria, but it looks like a gigantic virus."

JAD: Hmm.

ROBERT: What is gigantic—viruses are usually very small.

CARL ZIMMER: Exactly.

JAD: So a bacteria to a virus is like ...

CARL ZIMMER: Like, hundreds of times bigger.

JAD: Hundreds of times. Okay.

ROBERT: So it's the Queen Mary to a small dinghy.

CARL ZIMMER: Yeah. Right. So he looked up close and he was like, "What is this thing? This doesn't look right. This—this—if I didn't know better, I'd say this was a virus."

JAD: He's saying this based on its internal orientation?

CARL ZIMMER: Its appearance.

JAD: Because it had the protein thingy, it had the stuff?

CARL ZIMMER: So—so a lot of viruses, they have a shell made of protein. And the shell is kind of composed of plates. So it kind of looks like a soccer ball.

JAD: Ah!

ROBERT: Hmm.

CARL ZIMMER: So it's a very distinctive look.

JAD: Okay. And it looked like that.

CARL ZIMMER: It looked like that. It didn't look like bacteria.

JAD: Huh. Interesting.

CARL ZIMMER: He's like, "Wait a minute. Could this be a virus?"

ROBERT: So this would be like—maybe like finding an enormous soccer ball in the woods.

CARL ZIMMER: Yes.

JAD: So he's found the—the leviathan equivalent of that virus.

CARL ZIMMER: Right. It didn't make sense. It was kind of crazy in that microscopic realm to say maybe this is a virus.

JAD: Wait. So didn't—so Brad Mumford, what's his name again?

CARL ZIMMER: Timothy Rowbotham?

JAD: Rowbotham didn't have this realization?

CARL ZIMMER: Nope.

JAD: He hadn't looked at it closely enough?

CARL ZIMMER: He looked at it.

JAD: But he just didn't somehow put that this is a virus?

CARL ZIMMER: It didn't click for him.

ROBERT: It was a Tuesday, you know? Wednesdays are That's A Virus Day. And this was Tuesday.

CARL ZIMMER: And it's—it's likely that other people who were looking at these same things in years before.

JAD: And thinking they were bacteria and not relevant. Interesting.

CARL ZIMMER: Here's a big—here's something the size of bacteria ...

ROBERT: Well, in fairness, because viruses are always small, then you wouldn't think a big thing would be a virus.

CARL ZIMMER: Well, viruses are always small in the sense that they were discovered because they were small. Basically what scientists did was they discovered viruses by filtering fluid from a sick plant or a sick animal through a filter—porcelain, actually—and it was so small that—that anything the size of bacteria got trapped in the porcelain, and anything smaller came out.

ROBERT: Oh!

CARL ZIMMER: And lo and behold, they could find things that could cause sickness in that fluid that passed through the filter.

ROBERT: Oh, so the discovery of viruses meant it was innately small because that's how you filtered for them.

CARL ZIMMER: That's what they were looking for.

JAD: Interesting.

CARL ZIMMER: So there were probably generations of scientists who were looking in through the microscopes, saw some interesting round thing and assumed it was bacteria and it was probably a virus.

JAD: What the fuck is this giant, giant, leviathan virus? I assume that was his question.

CARL ZIMMER: [laughs] Well I mean, first he had to really establish that it was, and so what happened was that he looked very closely at it and kind of worked out its chemistry. And the more he looked at it, the more it looked like a virus. He started—he started actually looking at its DNA, which hadn't been possible before. Turned out that its DNA resembled the DNA of viruses and not of any known bacteria. It didn't have—it actually didn't have the equipment for making fuel inside of it. And then the real kicker was that he found out how to grow it. What he had to do was he had to stick this thing inside of amoeba.

JAD: Hmm.

CARL ZIMMER: And then out of the amoeba would come ...

JAD: More of the ...

CARL ZIMMER: ... more Bradford coccus.

JAD: Just like a virus.

CARL ZIMMER: Exactly like a virus.

JAD: So you need to change the name from Bradford coccus to something else.

CARL ZIMMER: Right. So they named it Mimivirus.

JAD: Mimivirus.

ROBERT: Mimivirus?

CARL ZIMMER: Mm-hmm.

ROBERT: Because they were in France, and Mimi is a—in a French opera?

CARL ZIMMER: Because it was a mimic. And it was mimicking ...

ROBERT: Oh, it was a mimic.

JAD: Oh, interesting. Mimi ...

ROBERT: A little—like a Mini Me.

JAD: Mimi? Is that like a French word for mimic?

CARL ZIMMER: I think they just took, you know, the beginning of mimic and added it to virus.

ROBERT: Oh, Mimivirus. Nice.

JAD: I guess it's the same thing twice: Mimi, it's like mimic. Yeah, okay. I get it. Interesting.

CARL ZIMMER: Yeah, so this was—I mean, this was really bizarre when they published the report on this in 2003, and then people really scratched their head because remember, you know, ordinary viruses have, you know, maybe 10 genes? This one had 1,018 genes.

ROBERT: [laughs]

JAD: Wow!

ROBERT: Wait, when you have 10 genes, those are the genes that—so you have a protein capsule and so you can swim through things, so when you land on a cell you can burrow in and then explode and then make babies. Those are—there's not much to being a virus. You just need a few genes for that. Why would you need thousands ...

JAD: Yeah. Does this thing have particular talents that the other viruses didn't have?

ROBERT: Yes. Maybe it's like ...

CARL ZIMMER: It does.

JAD: It does.

ROBERT: Oh, it does. Okay.

JAD: Okay.

CARL ZIMMER: Well, so what's—one thing that's really interesting is what happens when it goes inside its host, an amoeba. It goes in, but instead of kind of shedding off that protein coat and just spilling out its contents, it actually goes in and stays as it was.

ROBERT: You mean stays like in a container?

CARL ZIMMER: Yeah.

ROBERT: Oh.

CARL ZIMMER: It's called a virus factory. Once it's inside there, it's this thing they call a virus factory. And it basically is able to—to—things, components come into it, and then—then it sort of has enzymes that can refashion them, and then out come the components for new giant viruses.

ROBERT: Oh, but doesn't it have to go into the nucleus of the already-existent cell?

CARL ZIMMER: No. It just floats in there.

JAD: Oh, interesting! So it—it—what does it do ...

ROBERT: Oh, like, builds a little ...

JAD: Open a portal and it sucks up some stuff?

CARL ZIMMER: Yeah. It has this beautiful sort of—they call it a stargate.

JAD: Wow!

CARL ZIMMER: Because it's shaped like—it's a doorway shaped like a star. And things come in and then—and then at another stargate the sort of manufactured things come out. And then in the cell they assemble into new giant viruses.

JAD: Oh, so it spits out the raw materials and then self-assembles into a giant—a giant leviathan?

CARL ZIMMER: Mm-hmm.

ROBERT: No, baby giant leviathans, because then how do they get out of the—do they explode through the surface of the cell?

CARL ZIMMER: Yeah. They just blow out, yeah.

JAD: That's—that's like a totally—that's a totally different thing.

ROBERT: I've never heard of that. I thought normally viruses just go into the machine that's already there because they're parasites. They just use the living things ...

CARL ZIMMER: Yeah.

JAD: This thing is—I have a weird kind of respect for this thing.

CARL ZIMMER: Oh yeah, it's amazing. And, you know, one of the amazing things about it is that it can get its own viruses. It gets—there are ...

ROBERT: Really?

JAD: [laughs]

CARL ZIMMER: Yes.

ROBERT: [laughs]

CARL ZIMMER: So there are viruses of viruses.

JAD: Wow!

CARL ZIMMER: These things are called virophages, and they actually go into the virus factory and hijack it.

JAD: Oh, interesting!

CARL ZIMMER: And instead out come virophages.

ROBERT: Oh, wow!

JAD: Oh, yeah. Soon as you have a virus factory that's what a virus wants.

CARL ZIMMER: Mm-hmm.

JAD: So now the virus has its own virus factory. Well, it's gonna get—it's gonna ...

ROBERT: Virolized.

JAD: ... infected. Virolized by the other viruses.

CARL ZIMMER: Right.

JAD: Weird!

CARL ZIMMER: Very weird.

RZ: Yeah, weird is the right word, I think.

CARL ZIMMER: Right. Now in 2003, you know, you could say, "Well, this is one weird virus," but these scientists said, "Well, hmm. I wonder what else there is?" Like ...

ROBERT: Well, did they—did that sort of—wait a second. So they said, "Okay, it's got all this extra genetic power, but it's doing this sort of special circus act here. It's building its own factory, and it's just behaving differently from the—" so maybe it just needs all those genes to do this special thing it's doing?

CARL ZIMMER: The problem was that when they looked at these, you know, 1,018 genes, most of them didn't match anything anyone had found before.

JAD: Hmm. These are new genes.

CARL ZIMMER: Genes, yeah, that you couldn't even guess at what they were at.

JAD: This has gotta be from—this is like an alien. This is from Saturn, this thing. Is that where you're driving with the story?

CARL ZIMMER: Not quite, but kind of. I mean ...

ROBERT: So wait a second. So they look at all the genes, they look at the chemistry of life as it's known ...

CARL ZIMMER: Yeah.

ROBERT: ... and they don't find any matches for this little thing? This big thing?

CARL ZIMMER: For most of the genes, they couldn't find a match.

ROBERT: Huh.

CARL ZIMMER: You know, you can look at—I mean ...

ROBERT: Wow, that's a double mystery. Like, what is it? What is this, and where does it come from?

CARL ZIMMER: Mm-hmm.

ROBERT: Because it doesn't seem to have the smell of Earth life.

CARL ZIMMER: Yeah, except that it uses DNA. I mean, it uses protein, it uses our chemistry, but it's—it's doing something weird.

ROBERT: Hmm.

CARL ZIMMER: And so these scientists said, "Well, okay. They looked in an English hospital, you know, water cooling tower. Let's go look at one here in France." And so they looked and they found another giant virus, which is even bigger than the one that they had already found.

ROBERT: Where was it in the hospital in France? In the air conditioning unit?

CARL ZIMMER: It was in another cooling tower.

JAD: Geez, this is like a—this is a cooling tower phenomenon so far.

ROBERT: Yeah, rooftop biology.

CARL ZIMMER: Well ...

ROBERT: Excitement galore.

CARL ZIMMER: It's more like the drunk looking for the keys under the lamppost, you know?

JAD: [laughs]

CARL ZIMMER: It's like, you know that ...

ROBERT: Oh, because it's wherever you look there it is?

CARL ZIMMER: Because, like, we know that—we know there were giant viruses found in one water tower, so let's go look in another water tower. Like, that's our safest bet. And hey! Look, we found an even bigger one, you know, which they—which had ...

JAD: An even bigger one?

CARL ZIMMER: It was even bigger, yeah. So instead of 1,018 genes, it had 1,059 genes. So they named this one. Mamavirus.

JAD: [laughs]

ROBERT: Mimi's first cousin, Mama.

CARL ZIMMER: Right, right, right.

ROBERT: Did Mama do the things in the cells that Mimi didn't do? Or was it the same—did it also build a factory?

CARL ZIMMER: Yeah. It was—it was making a virus factory. So, like—so there's something—there's a common theme here with these two—now you have two giant viruses doing the same thing.

JAD: And this—the whole stargate and everything?

CARL ZIMMER: Yeah. What's weird is that, you know, the Mamavirus has a bunch of genes that Mimivirus doesn't have.

JAD: hmm.

CARL ZIMMER: So it's like—and again, don't match anything that ...

JAD: So they don't know what these extra ones do.

CARL ZIMMER: Some of them look like they're involved in building proteins, which doesn't make any sense because viruses are not supposed to do that.

ROBERT: Huh.

CARL ZIMMER: So it's—this is all completely confusing.

ROBERT: Huh.

CARL ZIMMER: But then they say, like, "Okay, maybe we need to kind of get away from the whole water tower thing and, you know, widen our little ..."

ROBERT: [laughs] Where would you go? Like, so the opposite of a water tower would be like the bottom of a well? Or is it—or do you go to a library and look in the interior of old parchment books?

CARL ZIMMER: No, you start looking at places like—you look—you look in the ocean, or you look in sediment, or you look inside animals, or you look in the soil. And they start finding giant viruses over and over and over again.

ROBERT: Really?

CARL ZIMMER: Yeah.

ROBERT: In all those places?

CARL ZIMMER: In many.

ROBERT: Soil? Inside of animals? Like, in animals' tummies or something?

CARL ZIMMER: Yeah, so they—they went to—these researchers went to Brazil and said, "Let's go look at animals and see if we can find giant viruses." And they found a new species in cows, and they found a new species living inside of a monkey.

JAD: Oh! And these were—were they finding gianter giant viruses?

CARL ZIMMER: Yeah.

JAD: I mean, the numbers of genes were going up and up and up?

CARL ZIMMER: Yeah, they would—they would keep finding new record breakers. So the biggest one right now is called Megavirus.

ROBERT: [laughs] That's the summer movie. Megavirus!

CARL ZIMMER: I mean there's, you know ...

ROBERT: Bigger than Mimi! It's bigger than Mama! Mega!

JAD: In a world ...

ROBERT: In a world ...

CARL ZIMMER: You got it. That's right. It's like truckasaurus, you know? Like, this is like—I'm wondering what they're gonna do as they keep finding bigger ones, because you keep having to find superlatives for this thing.

ROBERT: Hmm. Well, where was Mega found?

CARL ZIMMER: Mega, I believe, was found in the ocean.

JAD: And how many genes does Mega have?

CARL ZIMMER: Mega has 1,120 genes.

JAD: Oh, okay!

CARL ZIMMER: But it's not actually the big—so it has the most genes, but it's not actually the physically, the biggest giant virus.

JAD: Which was?

CARL ZIMMER: So this—this one is called a Pandoravirus.

JAD: [laughs]

ROBERT: It was found in a box. Let me guess. In a sealed box, and then they opened it and oh my gosh!

CARL ZIMMER: Well, it's—it has this bizarre shape like an urn.

JAD: Huh.

ROBERT: Oh.

CARL ZIMMER: Which is completely nuts. There's no urn-shaped viruses.

JAD: [laughs]

CARL ZIMMER: That's crazy!

JAD: And the urn, did that remind somebody of the myth of ...

CARL ZIMMER: So Pandora's Box was actually an urn.

JAD: Oh, it was okay. Okay. Oh I see.

ROBERT: Oh, it was? Why did they call it Pandora's Box then?

JAD: God, that's a very learned ...

CARL ZIMMER: Just to make you happy.

ROBERT: [laughs]

CARL ZIMMER: Because you'll love where they found it.

ROBERT: Where do they find it?

CARL ZIMMER: So what they did was these Russian scientists they were collaborating with dug up frozen tundra that had been frozen for 30,000 years and they said, "Let's thaw this out and see what's in there. What kind of things have been asleep for 30,000 years?"

JAD: That sounds like the beginning of a sci-fi movie right there.

ROBERT: Yeah.

CARL ZIMMER: Among other things, they found...

ROBERT: "In a frozen land ..."

CARL ZIMMER: They found Pandoravirus.

ROBERT: Huh.

CARL ZIMMER: And not only did they find it, but they—when they let it warm up a bit and then they gave it some amoeba to check out, they ...

JAD: It did its thing?

CARL ZIMMER: It did its thing.

JAD: Wow! And how much bigger—if the first giant virus you introduced us to was like an elephant-sized mouse, compared to that elephant-sized mouse how much bigger is this one? Maybe that's more specific than you want to be.

CARL ZIMMER: I'd need to look at the numbers.

JAD: Uh-huh.

CARL ZIMMER: But, you know, you're kind of going from, I don't know, elephants to dinosaurs. You're getting bigger and bigger and bigger. You're—you know, we're not talking about, you know, Pandoravirus is bigger than a lot of bacteria.

JAD: Wow!

ROBERT: So wait a second. So these things are now being found everywhere you look? I mean ...

CARL ZIMMER: They are incredibly common. They've even been able to get giant viruses out of people.

ROBERT: Really?

CARL ZIMMER: Yeah.

JAD: What's ...

ROBERT: Where are you finding them in a person?

JAD: In our intestines or something?

CARL ZIMMER: I believe they found one sample in somebody's lungs, and another sample was found in someone's blood. But it's really hard to tell whether they're actually, like, actively invading us and making us sick. You know, maybe instead of invading amoebas, they can invade human cells.

JAD: Hmm.

CARL ZIMMER: Because amoeba and human cells are surprisingly similar. Or is it just kind of along for the ride with some amoeba that infect us? Or does it kind of drift in, and when people are sick, their defenses are down. So we don't know if giant viruses have anything to do with human disease. But ...

JAD: It strikes me though, you have a category problem here.

ROBERT: Yes.

JAD: If you've got a giant virus that's virus-like in its general shell, but it's making proteins, it's got a bunch of genes that viruses don't have, you're already bigger than some bacteria, shouldn't we call it as its own separate thing at this point?

CARL ZIMMER: That's what people are arguing about right now. I mean, do we keep that line between viruses and cellular life and just put the giant viruses with the viruses, or do we kind of blur the line a bit?

JAD: Yeah, this feels like it's on its way from one category to the other.

CARL ZIMMER: So that's—that's one of the big questions is like, what way did this thing go in evolution?

ROBERT: What does that mean?

CARL ZIMMER: Well, how do you get a giant virus? Like ...

ROBERT: How do you?

CARL ZIMMER: How do you? Well, that—so ....

JAD: We'll get to the potential answer to that question, which I think is totally fascinating, after the break.

JAD: Hey, Jad here. Radiolab. So we're gonna return to our conversation, with science writer Carl Zimmer—it's an unedited conversation. And we were talking about giant viruses and what they can teach us about life, which really starts with a simpler question of, like, where the hell do they come from?

CARL ZIMMER: How do you get a giant virus? Like ...

ROBERT: How do you?

CARL ZIMMER: How do you? Well, that—so one clue comes from those genes. So now that they're finding more and more of these giant viruses, they're finding enough variety of them, they can look for some common genes that they share, some common mutations in genes. And they're finding actually that it looks like giant viruses might actually belong to one lineage.

JAD: Oh, interesting.

ROBERT: Oh, so they're cousins? They have a common ancestor?

CARL ZIMMER: Yeah. So ...

JAD: It's a tribe of a sort.

CARL ZIMMER: Right. And if—if that's true, it could be an incredibly old tribe. These giant viruses could be a lineage conceivably that, you know, goes all the way back to, you know, the early stages of life.

ROBERT: "The dawn of time."

JAD: "In a world ..."

ROBERT: "In a world ..." It's really old? Like, back to the very beginning of life on Earth?

CARL ZIMMER: To that era, yeah. Yeah. I mean, maybe when cellular life was getting started. But the question is well, what were the giant viruses like then? Now some people have said, "Well, no. Giant viruses actually started out as teeny tiny viruses, and they've just been, like, gathering up new genes through time and just been getting bigger and bigger bigger." But, you know, a number of the people who actually study giant viruses and have really, you know, helped us to understand the most are saying, "No, we don't think so. We actually think that these things started out as cellular life. They were cells. They were full-blown cells." And ...

JAD: Hmm.

ROBERT: Oh, you mean they were from the other side of the road? They were cellular life.

JAD: Whoa!

CARL ZIMMER: Yeah.

ROBERT: And then what, they switched sides?

CARL ZIMMER: Yeah. They changed teams, yeah.

JAD: How ...

ROBERT: How—no that—like, I can't have a plant that becomes an animal. [laughs]

JAD: How did they—so they've started off as like what we would call "creatures." And then ...

CARL ZIMMER: Right. They started out truly alive, you know, they ...

ROBERT: Like, freestanding, out there in the air or the water or the ground or ...

CARL ZIMMER: Yeah Yeah, just some, like, some free-living microbe.

ROBERT: Uh-huh.

CARL ZIMMER: Yeah.

JAD: And then ...

ROBERT: Then why would they be—why would you go demote yourself?

CARL ZIMMER: This is—this is your problem with parasites. You keep saying mean things about parasites.

JAD: [laughs]

CARL ZIMMER: How many years have we been talking about parasites? Have I taught you nothing?

JAD: [laughs]

ROBERT: If I had a choice between being a—having my own integrity and choosing to make a living on my own or to suck off you, I would just live on my own. Excuse me for—I know you like parasites, but honestly ...

CARL ZIMMER: Could you not use that passage in the recording, please?

JAD: [laughs] It's already been cut.

CARL ZIMMER: Thank you.

JAD: So wait a second. So you—according to this theory, you have a ...

ROBERT: It stands true nevertheless.

JAD: ... we have a microbe that is—that is doing its thing, and then something happens.

CARL ZIMMER: Okay, but ...

JAD: What is the something?

CARL ZIMMER: It becomes a parasite.

JAD: It becomes a parasite.

CARL ZIMMER: Or at least, you know, maybe a symbiont. Basically, what it does is it starts living inside another cell.

ROBERT: You mean it gives up its integrity as a free life form, a free-standing life form.

CARL ZIMMER: Mm-hmm.

JAD: Just so we understand what that means, that means that it's got a shell, it's got a border, it's making its own energy, it's replicating in the way that ...

CARL ZIMMER: At the beginning.

JAD: At the beginning.

CARL ZIMMER: At the beginning it can make its own energy. It can grow, it can divide.

JAD: It can do all the things that living things do.

CARL ZIMMER: Yeah.

ROBERT: And then for some reason, it chooses to require some other creature's existence for its own. It has—it has to become dependent on some other organism for its very—very existence.

CARL ZIMMER: Well, let's flip it the other way and say it discovers a wonderful new home inside of another cell. It comes in and is like ...

ROBERT: Just like I love leaving my Park Avenue apartment for a dark cave.

CARL ZIMMER: No!

ROBERT: It's a new and exciting opportunity, real estate-wise.

CARL ZIMMER: No, no, no. Au contraire. Au contraire. Like, imagine you're like—let's imagine you're, like, Bear Grylls, okay? Let's imagine you are, like, hiking around and killing your own food, okay? Let's try to picture this, okay?

ROBERT: [laughs]

JAD: Robert doing this?

CARL ZIMMER: You're gutting your deer, you're starting your own fires, you're going on and on and on. And you do that for, like, a few years and then—and you're walking through the jungle ...

JAD: And you're very, very skinny because it's not going well.

CARL ZIMMER: So Robert Krulwich, the haggard hunter—and let's say you're doing this in Minnesota, all right? So it's like cold, okay? And then suddenly, like, you—there's a break in the forest and you come across a giant mansion. And you're like, "What is this place?" And you open the door, and inside there's, like, conveyor belts with ice cream and steak. And—you know, and there are slippers waiting for you. And, you know, anything you need. It's—somebody else is taking care of it.

ROBERT: There is one thing you left out. When I walked into this magical kingdom of sorts, it doesn't let me out. I can't leave ever again.

CARL ZIMMER: Sure you can.

ROBERT: Because I have become so dependent on its natural wonders that I lose my independence, my integrity and the very, very thing that I walked in with is now gone. I'm stuck inside.

CARL ZIMMER: We did literally have this conversation a few years ago.

JAD: We did. It's true.

CARL ZIMMER: We did. And I did point out to you at the time that you are quite dependent on other species. Do you want me to bring ...?

JAD: No, no, no, no, no!

CARL ZIMMER: I will just—I will just say see episode 32 or whatever.

ROBERT: Jad's eyes will roll right out of their sockets.

CARL ZIMMER: Yeah. So—so, like, becoming—being able to take advantage of another cell, evolutionarily speaking, is a great way to go.

JAD: Mm-hmm.

CARL ZIMMER: Because you have all these things taken care of for you. Now the—according to this theory, these mysterious ancient microbes started going into these cells and reproducing there, and then going out again and then finding another host cell to infect, okay?

JAD: Were they making—like, were they making their hosts sick?

CARL ZIMMER: Probably, yeah.

JAD: Probably.

CARL ZIMMER: Yeah. Because giant viruses are not good to get.

JAD: See, this is—this complicates your mansion metaphor just a tiny bit because what it means is that you go to the conveyor belts and you're feeding yourself and having a good time, but then your filth starts to muck up the place and it starts to collapse from within. That doesn't sound so nice.

CARL ZIMMER: To strain the metaphor a bit ...

ROBERT: Go boy! Go boy!

CARL ZIMMER: Robert Krulwich. Robert Krulwich.

ROBERT: Stop referring to me. Now let's go to him.

CARL ZIMMER: Okay.

JAD: No, I'm just trying to understand.

CARL ZIMMER: So—so you spend some time in this wonderful mansion. You rest, it's warm, it's comfortable and so on. You eat.

JAD: You fill it with your filth.

CARL ZIMMER: You start a family, you know? And then all of a sudden, you and your descendants, you know, leave the mansion. The mansion just collapses ...

JAD: [laughs]

ROBERT: [laughs]

CARL ZIMMER: ... from all the damage you did to it. But, you know, actually you see in the distance there's another mansion. Let's just go over there. Now you feel, like, rested and ready and, like, yeah, all we gotta do is get over there. So let's just go there. We don't have to—we don't have to stop to kill a deer. We just go to that next mansion. The ice cream is waiting.

JAD: I still gotta walk, so I need my legs so to speak.

CARL ZIMMER: Yeah. Sure, sure.

JAD: Just to get to the next mansion.

CARL ZIMMER: Right.

JAD: But I don't need the powerful muscles that I would have needed to kill the deer. I can let go of those.

CARL ZIMMER: You don't even—you don't even need—you know, let's say that you were—you know, you don't even need the knowledge of how to kill a deer.

JAD: [laughs]

ROBERT: He would be blind, dumb and fat. That's where you end up.

CARL ZIMMER: So these things, these things ...

ROBERT: And destructive.

CARL ZIMMER: ... they start getting rid of these genes.

JAD: And how does that happen?

CARL ZIMMER: Just, you know, a random mutation comes along and just cuts out a bit of DNA.

ROBERT: Oh, because it doesn't need them.

CARL ZIMMER: You're fine. Yeah. You're like, "Okay."

JAD: Is it a moment where—bloop—oh, there goes a big chunk of me. Gone. I don't need that.

CARL ZIMMER: Yeah. That's a regular kind of mutation. That happens all the time in cells.

JAD: Really?

CARL ZIMMER: Oh, yeah. Yeah.

ROBERT: But then your—your successor being—just travels a little bit lighter and is able to succeed just as well.

CARL ZIMMER: Right. So, you know, if—you know, if we are born, you know, with a part of our DNA that's deleted that had some, you know, like, hemoglobin genes in it, like good night. Like, that's bad. I mean, but—you know, but if you cut out a gene that this giant virus no longer needs because it's got everything supplied to it in its host? Fine. So let's chuck that—chuck it out. So you have this—so the idea is that you—these viruses, they're giant viruses, but they've actually been shrinking.

JAD: Huh. At a—how fast does a giant—like the—imagining back in the beginning there was—there was not Mega, not Gino but, like ...

ROBERT: No, it began as a cellular being, right?

JAD: Oh, a cellular being. Right. Okay, so this ...

ROBERT: A cellular being.

CARL ZIMMER: A cellular being.

ROBERT: With all of the privileges and joys of independent life.

JAD: [laughs] Size-wise, it's a blimp, it's a massive thing. And then suddenly, it starts to shrink bit by bit by bit by bit. At what rate does it start to shrink and shed itself?

CARL ZIMMER: Well, it could be that these giant viruses we're finding, these giant viruses that scientists are finding could be shrinking very, very, very slowly.

JAD: Hmm.

CARL ZIMMER: It could be that there are other viruses that made this transition that shrank faster.

ROBERT: Hmm.

CARL ZIMMER: So maybe, maybe ...

JAD: It's a race to the bottom.

CARL ZIMMER: Maybe some—some—maybe some tiny viruses are just former giant viruses that just shrank really fast.

ROBERT: Wow, race to the bottom! It's such a different way of thinking about life. You—you generally assume, being a multicellular organism yourself ...

JAD: Yeah.

ROBERT: ... that little things in some deep sense, even though you're not supposed to say this, want to be big things.

CARL ZIMMER: You don't want to say this.

ROBERT: I know, I know. But most people unlike you, asshole, most people think that it's better ...

CARL ZIMMER: Now that I want in the podcast.

ROBERT: [laughs] It's better to be more complex than to be simple. But here you're talking about a different voyage all together. It might just work out for you to be simple rather than complex.

CARL ZIMMER: Well, given that—that viruses are insanely abundant on this planet—I mean, there are, by some estimates, 10³¹ viruses on Earth. Think about that. Like, it's a—you know, it's a one with 31 zeros after it. I mean, it's inconceivable how many viruses there are on Earth.

JAD: It's their world.

CARL ZIMMER: So apparently, you know, nature has not agreed with you.

ROBERT: [laughs]

CARL ZIMMER: But, you know, it is interesting, like, thinking about how—how life gets smaller and simpler.

JAD: It's interesting, yeah. If it's true that this trajectory is as common as you say, that things start out—sometimes start out big, and then learn to live inside other things, and in the process get smaller and smaller and smaller, and this is actually maybe what happens to a lot of viruses, not just some viruses, in a way it gives the virus an honorable history. I don't know why I feel that way.

ROBERT: Now this boy isn't gonna sign up for that.

JAD: No, he's not gonna sign up for that, and I don't ...

CARL ZIMMER: That's okay. Well, an honorable history, but then, I mean, it abandoned its free-living past, right?

JAD: It did.

CARL ZIMMER: It gave in to the temptations of the mansion full of steak and ice cream.

JAD: It's true, but I've always assumed—and this is not something one should assume—that viruses were a kind of proto-organism. They were somehow at the beginning of something and they never quite got going.

CARL ZIMMER: Yeah.

JAD: But this—you're actually saying that these viruses are, in a way, at the end. Not at the end, but they're at the—I don't know how to quite use the words that I want to use. They feel somehow at the end of something, not at the beginning. Like, you've just took the—you just took what I consider to be the beginning and you've now made it an end.

ROBERT: An end.

CARL ZIMMER: Mm-hmm.

JAD: And that's interesting. I never ...

ROBERT: Yeah, that's very interesting. Yeah, very interesting.

CARL ZIMMER: So—so life can go in different directions.

JAD: And how far can that reverse journey go? I mean, can you go from, like—how big did that—was it ever like a turtle with—with things?

CARL ZIMMER: No.

JAD: Or like a giant dinosaur? No?

CARL ZIMMER: No. Sorry. There are things called—I believe they're called myxozoans, which started out as free-living animals and have become parasites. And they're just down to just a few cells.

JAD: Wait, wait, wait, wait, wait. Myxozoans? You say free-living animals, you don't mean animals in the way that ...

CARL ZIMMER: Animals-animals.

JAD: ... anyone would think of an animal.

CARL ZIMMER: Like a jelly ...

JAD: Like, "Oh, look: my pet Fluffy." Not like that.

CARL ZIMMER: More like, "My pet jellyfish."

ROBERT: Really?

JAD: Really?

CARL ZIMMER: Yeah!

JAD: So you're saying a jellyfish-sized thing has now reduced itself to a tiny speck?

CARL ZIMMER: To a microscopic parasite of fish.

JAD: Get the fu ...

ROBERT: Don't even say it, because you can't do it if you're that small.

JAD: That's insane! Really? Like, going from something you can see and would want to avoid while swimming, down to something that you might even just breathe in without even knowing it.

CARL ZIMMER: Mm-hmm.

JAD: Wow! You're blowing my mind! Shrinking my mind.

ROBERT: What was it called again?

CARL ZIMMER: Myxozoans.

JAD: Myxozoans.

ROBERT: A myxozoan?

CARL ZIMMER: Yeah.

ROBERT: How do you spell that?

CARL ZIMMER: M-Y-X-Z-O-A-N.

JAD: I'm trying to, in my mind, to construct a scenario where we, like the myxozoan, could begin to shed. Like, if we were living inside the—like, not the iPhone, but the iHome, the iUniverse.

CARL ZIMMER: Well, you know, but the fact is that we have cast aside some things, you know?

JAD: What have we cast aside?

CARL ZIMMER: Well, we can't ...

JAD: I mean, we used to smell better. I know—I know that.

CARL ZIMMER: We used to smell better. We used to be able to make our own vitamin C in our own bodies. Our own bodies were vitamin C factories.

JAD: Really?

CARL ZIMMER: Yes.

JAD: What—what changed that? Why did we want to let go of that? That sounds great.

ROBERT: Sunshine. Vitamin C.

CARL ZIMMER: Yeah. Making your own supply of vitamin C. Well, if you are sitting around eating fruit all the time, fruit which is loaded in vitamin C, then if you get a mutation on your vitamin C gene well, you're fine because you're getting your vitamin C from somewhere else. You don't feel that lack, you know?

JAD: I see.

CARL ZIMMER: You don't start getting scurvy because you're feeding yourself on fruit. And then that mutated gene may then spread out and end up being in every member of your species, which seems to have happened to us. I mean, you can literally, like, see, like, these—we have these broken vitamin C genes.

JAD: Huh. So sometimes we shrink, too.

CARL ZIMMER: Yeah.

JAD: Okay, so there you have it—a raw conversation with science writer Carl Zimmer about shrinking, shrinkage in life. Now usually what happens in these conversations is because you're just talking, and because you don't really have, like, an encyclopedia sitting right next to you, you get a lot of the little things wrong: little details, little facts, names, dates, whatever. And then, you know, you fact check it later. So in fairness to Carl, as we were fact-checking, we gave him the chance to listen back to the raw conversation and make a couple of amendments.

CARL ZIMMER: This is fact-checker Carl scolding rambling Carl.

JAD: Okay. [laughs]

CARL ZIMMER: Okay, we were saying that this microbiologist Tim Rowbotham took his samples to France, but actually there was another microbiologist named Richard Birtles that did it.

JAD: Gotcha.

CARL ZIMMER: So, small but important.

JAD: Sorry, Richard.

CARL ZIMMER: Our apologies.

JAD: Yeah.

CARL ZIMMER: And Mamavirus turns out to have 1,023 genes not 1,059 genes. My apologies. Then I started talking about Megavirus. At the time in 2011, it was indeed the biggest virus known. 1,120 genes, okay?

JAD: Okay.

CARL ZIMMER: However, there was, in 2013, another virus found called Pandoravirus. Now I was saying that this was something found in the Siberian tundra. Wrong. This was found in the ocean.

JAD: [laughs]

CARL ZIMMER: And this virus has a whole lot of genes.

JAD: How many?

CARL ZIMMER: It has 2,500?

JAD: Whoa!

CARL ZIMMER: 2,500. I mean, that's way more than a lot of bacteria.

JAD: Also, at a certain point we do refer to Pandoravirus as being the biggest virus in size. Actually, that distinction goes to Pithovirus. And also, it seems that since we talked, there's evidence that there might actually be a couple separate lineages of giant viruses. One may have evolved from big to small as we talked about, but another one might have gone in the usual direction, from small to big.

CARL ZIMMER: There's one last thing that I see. So apparently—apparently I didn't quite spell myxozoan correctly.

JAD: [laughs]

CARL ZIMMER: This is how you spell myxozoan: M-Y-X-O-Z-O-A-N. Apparently, I missed one of those Os. I can't remember.

JAD: I mean, I'd be lying if I say I didn't think a little bit less of you now.

ROBERT: [laughs]

JAD: Okay. Extra O. Back in.

CARL ZIMMER: The raw stupidity that goes into Radiolab. Stupid people interviewing stupid people.

JAD: [laughs] About smart things. That's funny. That's a great tagline. Okay, that's our new tagline. I'm Jad Abumrad. Thanks for listening.

[LISTENER: 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, Ekedi Fausther-Keeys, W. Harry Fortuna, David Gebel, Maria Paz Gutiérrez, Sindhu Gnanasambandan, Matt Kielty, Annie McEwen, Alex Neason, Alyssa Jeong Perry, Sarah Qari, Sarah Sandbach, Arianne Wack, Pat Walters and Molly Webster, with help from Timmy Broderick. Our fact-checkers are Diane Kelly, Emily Krieger and Natalie Middleton.]

[LISTENER: Hi, my name's Michael Smith. I'm calling from Pennington, New Jersey. 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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