What Are The Weirdest Types Of Life? - Carl Zimmer | Modern Wisdom Podcast 394

1. 0:00 – 0:38

   Intro

   1. CZCarl Zimmer0:00

      Let's put it this way. There are other species that can recognize things that are alive and are not alive. That doesn't mean that they have, like, a deep conceptual understanding of life. But, you know, you could argue that we don't really either. (laughs) You can see different behaviors that animals have in response to living and dead things. You can see that, uh, that some animals are, are very good at recognizing biological motion, that is the movement of living things, and can distinguish that from the movement of things, you know, like rocks or something that are moving but are not alive. And that's really important for a lot of species.

   2. CWChris Williamson0:35

      Carl Zimmer, welcome to the show.

   3. CZCarl Zimmer0:37

      Thanks for having me.

2. 0:38 – 10:09

   Our Awareness of Life

   1. CZCarl Zimmer0:38

   2. CWChris Williamson0:38

      It's an interesting thing talking about life and what it constitutes, right? Because I think a lot of people have heard about discussions to do with euthanasia and assisted suicide, and is this person really alive, what does it mean, philosophical arguments to do with is somebody in a coma, uh, discussions around abortion, what constitutes life during, um, childbirth and, and beforehand. And yeah, it's an interesting, an interesting area. It seems like it sort of coalesces a lot of big questions that people have.

   3. CZCarl Zimmer1:12

      Uh, it really does. Um, a- and, but at the same time, uh, for as important as it is, um, there hasn't been really all that much, um, thinking among scientists about, you know, life with a big capital L. I mean, when we talk about life, w- what do we really mean? Um, and so what's really astonishing is that, you know, you can find plenty of definitions of life, uh, in the scientific literature, um, but there are different definitions. And I find if I, if, uh, I start talking about life with a scientist, um, they might very well have a definition and it's different from the one I heard from the last person. Um, so y- you have this situation wh- which is really strange. I mean, imagine like in chemistry people didn't agree on what an atom is. I mean, (laughs) that would be kind of problematic. And yet we're in this situation where scientists who study life, life in different forms, they just, they really don't agree on what it is they're talking about.

   4. CWChris Williamson2:12

      Why is it so messy?

   5. CZCarl Zimmer2:15

      Um, you know, that's a good question. I think, uh, part of the problem is that, uh, i- is, is that sometimes we're trying to get at different things when we use the same word. So, you know, um, there are these, uh, issues about end of life, you know. So, um, is someone who's on a ventilator, are, are they alive? Um, and so we start to talk about, um, uh, you know, brain death as being sort of the definition of the end of life. Um, but that's really the end of one person's life, um, you know, their state of being alive. Um, whereas other people want to say, "Okay, um, you know, a snake and a tree and me, we, we all have something in common that's different than a rock. Um, what am I gonna call that?" And people will say, "Well, that's life." And so it's a, and so it can be a way of trying to pull things together into s- and trying to figure out what they have in common. Um, but, you know, e- but even then you get yourself into trouble because then, you know, you think you kind of have a nice little category of things that are alive and then someone comes along with something else, like a virus, and then everyone starts yelling all over again. Um, so, so it's, it, it's a, it's marvelously prone to lead to big arguments.

   6. CWChris Williamson3:44

      Whose job is it to work out what life is? Is it biologists, chemists, philosophers?

   7. CZCarl Zimmer3:51

      It's funny. Like, I mean, if, if you talk to, uh, a typical biologist, you know, I, I talk to biologists all the time for my work, and, um, if you, uh, kind of stop the conversation and you say, "Oh, by the way, I'm kinda curious, like, um, what's, what's your definition of life? I mean, what, what does it mean to be alive?" Um, a lot of them actually don't want to really, like, talk about that at all.

   8. CWChris Williamson4:15

      Why?

   9. CZCarl Zimmer4:15

      Um, well, because, you know, y- you might be a scientist who, let's say you're a, a scientist who, uh, studies tigers and you really like tigers, um, and you don't know a whole lot about, uh, you know, uh, fungi. They're fine. Um, you know that your tiger and the fungi have some things in common, but, like, it's not really your job to, to get too into that. Like, there's enough to do with the tigers. So, um, s- so for a lot of scientists, like, life is so big and so complicated and so overwhelming that they really just want to kind of zero in, um, you know. I mean, somebody, you know, there are some people who just want to study, you know, one protein. Um, i- uh, so that's even smaller, you know. And, and you can get a lot of, you can get a lot out of that as, as a scientist. You can learn a lot. But it is a little awkward when, like, this, you know, you, as a biologist you are studying life, right? And yet, um, it's, it can be really hard (laughs) for, to get a straight answer out of scientists about that. But, um, you know, so it's, so it, so then it's fun to find the, the people who really are thinking about life, um, and, and to get, and who are even trying to do research on, on, you know, life itself, a- and to, to figure out, f- to learn what they're trying to do and how they're grappling with it.

   10. CWChris Williamson5:40

       Uh-

   11. CZCarl Zimmer5:40

       But it's definitely a minority.

   12. CWChris Williamson5:41

       Would you say that humans are the only animals that are aware of life and death?

   13. CZCarl Zimmer5:46

       No, actually not. I mean, and, uh, uh, let's, let's put it this way. Um, other, there are other species that, um, can recognize things that are alive and are not alive.You know, um, that doesn't mean that they have, like, a deep conceptual understanding of life. But, you know, you could argue that we don't really either. (laughs) Um, so, you know, for example, like, I mean, you know, a fish swimming along, um, can tell that there's something dead nearby and will avoid it. You know, that they... You can see different behaviors that animals have in response to living and dead things. Uh, you can, uh, you can see that, uh, that some animals are, are very good at, um, sort of recognizing biological motion, that is, the movement of living things co- and, and can distinguish that from the movement of things, you know, like rocks or something that are moving, but are not alive. Um, and that's really important, uh, for a lot of species. You know, um, y- you, you want to, you want to avoid, you know, cadavers that could make you sick. Uh, you want to, um... If y- if something's moving, um, that could be a predator that's gonna kill you, or it could be a rock that's tumbling down and, you know, that could kill you too, but you need to respond in different ways. You know, the rock isn't gonna come after you. The predator might. So, um, so there are good evolutionary, uh, benefits to being able to recognize life and death. And we can probably... We... Our own sense of life, you know, that we ourselves are alive, um, that probably has these deep evolutionary roots too, um, just sort of monitoring our own bodies and that kind of sense of being alive. It's not like an, a, a rational deduction. You know, we don't say like, "Ah, from these, these certain things, I deduce that I'm alive." It's just you feel alive. And what's fascinating is that, you know, the flip side is that there is actually a syndrome, a psychological syndrome, where people are convinced that they are dead. And they will tell you that they're dead, and they'll explain how they died and how it is that they're still able to talk to you after death. It's called Cotard Syndrome, named after a doctor who first recognized it in a patient in the 1800s. So, um, so I actually think that, like, this sort of deep ability to recognize life and death, um, actually kind of gets in the way, uh, of our trying to understand life scientifically. Um, e- because we sort of, we sort of assume that it's gonna be easy, you know, 'cause it feels easy, but it's... Really, if you're trying to understand life, uh, as, as scientists, it's not easy at all.

   14. CWChris Williamson8:31

       What are some of the stories that the patients that have that Cotard Syndrome will tell the doctors?

   15. CZCarl Zimmer8:37

       Um, well, they'll say, "Well, I, you know, I drowned in a lake last year, and I've been a zombie ever since." Um-

   16. CWChris Williamson8:44

       But they're breathing. They're talking. They're telling this to them.

   17. CZCarl Zimmer8:48

       I, I, what can I tell you? Like, uh, uh, the, these are the things that you see in these, in these accounts, you know, and I'm sure, I'm sure that the, the psychiatrists or the doctors were trying to, like, get that out of them. Like, really? Like, how does that happen?

   18. CWChris Williamson9:01

       There was one lady who was, uh, worried about being washed down the drain or something, wasn't there?

   19. CZCarl Zimmer9:06

       Yeah. So, uh, it, it's pretty common, uh, in these reports of Cotard Syndrome. It's very rare, but there are enough reports that you can kind of see some patterns. And there is this feeling that people have that they're just a husk. They're sort of empty inside. There's just nothing there. And, uh, yeah. And so one woman was saying that that's why she never bathed, because she would just wash away down the drain. Um, and, uh, it's, it's, it's astonishing. Um, and, you know, what... There, there is just one report that I've seen where th- where some scientist tried to actually, like, uh, uh, look at the brain of someone with Cotard Syndrome. And, um, and what was interesting was that there, there did seem to be some damage to a part of the brain that's involved in monitoring the body, sort of taking in information from different parts of the body and kind of integrating that into a, a feeling. Um, and, uh, so if you're not getting those signals, then you just feel, "Well, hmm. I... There's nothing there. I don't feel alive. Therefore, I must

3. 10:09 – 20:45

   What Constitutes Life & Death?

   1. CZCarl Zimmer10:09

      be dead."

   2. CWChris Williamson10:10

      What are some of the current working definitions of what constitutes life and death?

   3. CZCarl Zimmer10:16

      Uh, there are... I mean, there are literally hundreds. Um, but, you know, I think the m- perhaps the one that you see most often, uh, came about, um, at a meeting of scientists in the 1990s brought together by NASA. You know, NASA w- wanted them to come up with a, uh, a plan for, uh, looking for life elsewhere in the universe. And they pretty quickly realized, like, "You know, we need to, like, agree on what we're talking about. You know, what are we exactly looking for? You know?" Um, and, uh, so, you know, because, like, you don't want to say, like, "We're gonna look for h- human beings." You know, like, no matter what you see on Star Trek where everybody seems to look just like us on other planets, um, y- you need a broader definition, so... Or at least a working definition. And so, they, they settled on something, uh, it was basically that, you know, that life is a, is a, uh, uh, a chemically self-sustained system capable of Darwinian evolution. So that's what they, that's what they settled on. Uh, and so you can find other ones that, um, where people emphasize other things, uh, you know, that they really emphasize m- metabolism or, you know, anything, anything capable of evolving is, is alive or what have you. Um, uh, but, you know, I'd say that the, the NASA, uh, definition is, is perhaps the, the most common one you'll see. Maybe because it's one of the shortest.

   4. CWChris Williamson11:52

      All right. So that's life. What about death? Just that stopping in a system that used to have it?

   5. CZCarl Zimmer11:58

      Well, you know, NASA did not, uh, ask scientists to define death. (laughs) And, uh, you know, really, like, they were just more interested in, like, the presence of life versus the absence. So, like, you know, the moon is not alive. The moon is not life, you know, because the moon is a rock. Uh-

   6. CWChris Williamson12:15

      But is it dead?

   7. CZCarl Zimmer12:17

      Um, well, um, e-It br- I mean... Okay. I don't... Y- No scientist would, like, use the language of death to describe the moon. You know? They would... Might say it's abiotic. You know? In other words, not having anything to do with life. Uh, it was never alive. Um, but yeah, defining death becomes a big challenge. Um, and, uh, you know, just, just in medicine it's been, uh, very challenging, um, for, for centuries really. I mean, physicians had this problem where some of their patients, you know, they, they didn't seem very alive, but were they dead yet? You know? Like, was it, was it time to, you know, dig a grave for them? And, um, you know, there was a great terror actually in the 1700s and the 1800s that people would be buried prematurely. And so you could actually, um, request to be buried in a coffin that would have, like, a little hole in it with a, with a, like a wire that could run out of it.

   8. CWChris Williamson13:16

      There's a little bell, doesn't it?

   9. CZCarl Zimmer13:18

      Exactly. Exactly. Yeah. In Germany in the 1800s, in the late 1800s actually, there would be these sort of, um, uh, kind of like funeral parlors, but really what they were are they were just, like, people would be taken to these... These were very large buildings, and they'd just be put there just for a few days, just laid out. Just... And, and again, they would have a little bell there just in case, um, they came back. Um, they didn't, but, um, but there was this anxiety because no one could really say, like, "Boom, this person is dead." You know? The stethoscope obviously helped things a lot, because, you know, if you waited for a while and, you know, there was no heartbeat, then, you know, maybe we could agree on that. Um, on the other hand, if someone had been, you know, um, uh, you know, uh, suffered from hyperth- uh, uh, hypothermia, you know, that might be kind of ambiguous. The big problem for us came about, um, through the invention of ventilators. So you would have these situations in which, um, someone, you know, had massive brain damage and, uh, would be unable to, uh, to even breathe on their own, because they, they lacked the connections to the brain required for breathing. So you would, uh, you know, put these people on ventilators, um, and, you know, some of them might be able to recover somewhat. Um, most of them just, you know, lived for a couple days at most and then died. Uh, and, you know, in the 1960s, this is actually at the time when organ transplantation was becoming a reality, and, uh, these transplant surgeons were saying like, "Here are all these people who are really... They're, they're effectively dead. They're, they're gonna be dying very shortly, and we need organs." You know? And if we wait for people to die and then go about taking organs, those organs are degraded, you know, so they're worse for the, for the people receiving them. So what if we were to say brain death is death? Or what if we just say, like, "There's no hope that this person is coming back. That's it." You know? And so we could... You know, if they want to donate their organs, now is the time we do it. Um, this is more, you know... Th- this... A lot of this is, like, a, a social agreement, you know? You can't say it's our pure science. It's us as people making a decision about these very difficult situations, not just the difficult situation of the person who's on the ventilator, but the difficult situation of the person who's gonna die if they don't get an organ. Um, and, you know, there can... There have been... You know, sometimes there have been conflicts over that. You know? So for-

   10. CWChris Williamson16:02

       Yeah. You can see how perverse incentives could arise here.

   11. CZCarl Zimmer16:06

       Sure. Sure. And, but also you can see how, uh, if people don't agree with this particular definition of life and death, that they might say like, "No, um, we don't want you to declare our daughter dead." And this actually is a case that happened I write about in the book, um, where, um, a, a, uh, girl in California, um, you know, she, she went on a ventilator, suffered massive brain damage and went, went on a ventilator after a surgery that had gone bad, and her family didn't want her declared dead. Um, and so she w- she was actually flown from California, where a death certificate had been issued, to New Jersey, where there were these religious exceptions, uh, made. And she actually was taken off the ventilator, and, um, she was s- she was able to live for several years, you know, in this state. Um, uh, you know, she went through puberty. Um, uh, you know, the... She was... I should say she was still on the ventilator, but, you know, her body was continuing to grow and to mature. So, uh... And then she died of internal bleeding, and then got a second death certificate. You know? It's so... It's, it's an extreme exam- uh, demonstration of how hard it can be for us to agree on what it means to l- be alive and then what it means to be dead.

   12. CWChris Williamson17:27

       What about cryptobiotic species?

   13. CZCarl Zimmer17:31

       Yeah. Cryptobiotic species are amazing. Um, and, uh, they are... They are these, these, uh, animals and, and other species that just totally, like, make fun of us, uh, (laughs) in terms of our, our notion that there's a clear dividing line between life and death. Um, so one example are these little animals called tardigrades. Um, they're barely visible to the naked eye. They're in the soil. They're, uh, in the ocean. They're all over the place. And, um, they're sometimes called water bears because, uh, they, they have this cute kind of bear-like appearance. Um, and what's amazing is that, um, if, if, if they're in a si- a situation where they're, they're in a drought, where their, their environment is drying out, um, this is a situation where we would just die. I mean, if you, if you lost a substantial amount of water from your body, your biochemistry falls apart. You're dead.Um, they don't die, however. They, they can actually survive for decades, maybe over a century, completely desiccated. Um, they have been sent out into space and then brought back, and if you just put them back in water, they're back to the way they were before. And so scientists are trying to under- understand, well, what do the water bears do? What do these tardigrades do? And what they seem to do is, they, they do these amazing, um, chemical tricks to, to, uh, to go into this state that sometimes people call a third state, cryptobiosis. Um, they, uh ... And, and one of the key things that they do is they start making a special kind of protein that encases all of their essential molecules in their cells, kind of like glass. So that you can imagine that these animals are basically turning themselves into a kind of a protein glass. Nothing's moving. Um, and if nothing's moving on a molecular level, you can't say that you're alive by most definitions of life. I mean, there's no, uh, chemical activity. There's no metabolism. That's just not happening. But they're not dead. In other words, they're not falling apart. They're not disintegrating. Um, they're just on pause, and can stay on pause for decades, maybe centuries. Um, and, uh, and turns out, there are more and more of these species, um, plants, fungi, that may be able to do the same thing.

   14. CWChris Williamson19:55

       Yeah, so that defeats my previous definition of death, being an absence of a thing that used to be alive.

   15. CZCarl Zimmer20:03

       Right. I mean, I, I think, you know, you are thinking about, you're thinking about death, you know, uh, uh, human death, you know, the death we know best, you know. And, you know, for the most part, um, you know, if there's an absence of certain key things, you know, if it ... If you can't breathe, if your heart stops, if your brain's not working, like, boom, everything's gonna fall apart, um, and you're, and you're not coming back. Um, but that's just, that's not a universal rule. It doesn't have to be that way, um, that, you know, uh, life doesn't really care about our absolutes that way.

4. 20:45 – 25:48

   Animals with Weird Ideas About Life & Death

   1. CZCarl Zimmer20:45

   2. CWChris Williamson20:45

      What about some other animals, some of the interesting creatures that you found in your research for the book that have weird, weird ideas about life and death?

   3. CZCarl Zimmer20:54

      Uh, yeah, well, uh, you know, there are certainly, um, things that, uh, features of living things that, that people talk about a lot, you know, hallmarks of life, sometimes they're called. And so one of the hallmarks is metabolism, um, the ability to, to take stuff in, to, to, to use it to generate energy and to, to produce biomass. And, uh, you know, metabolism is, is, chemically speaking, it's really similar in some fundamental ways from species to species to species. I mean, anywhere you look, metabolism, uh, is, involves this one molecule or, or, or basic fuel, ATP. Um, so bacteria, they, they're making ATP, we're making ATP, snakes are making ATP. Uh, but there are just some, there are some species that are just really amazing, metabolically speaking, uh, and, and really stand out. They're, they're exemplars. And so one example is, is certain kinds of snakes like boa constrictors or pythons. Uh, and so I, I, I went to, to visit a scientist who studies them and hung out with some of these massive snakes, these amazing animals. And, you know, they, they can go for weeks without eating anything, um, and they're fine, and then, uh, then, you know, they can suddenly, like, leap into action, attack something, um, whether it's someone feeding them a rat or if they're, you know, a python out in the wild, might kill a deer, um, and then they will suddenly swallow something there that can be their own weight and then break that down. So over the next few days, they completely digest it all except for a little pod of fur coming out the other end. Um, and so there are some scientists who have been studying this, this amazing feat of metabolism. Um, it, it's, it's not, it's not easy to do this. It actually ... You know, they're, they're eating these things to get, uh, energy out, but they have to put a lot of energy in, you know. They have to, they have to make an investment to get all that return. Um, and so, you know, part of what is involved is they have to basically, like, retool their whole body, like in a matter of hours. So like, as soon as they're starting to swallow something, all sorts of things start to happen in their bodies. Their intestinal walls double in li- in thickness. Um, their hearts, uh, increase, I think it's about 50% in size. Their livers get bigger. I mean, and we're t- again, we're talking about this happening in a matter of hours. Uh, and so that way, they're a- they're ready to handle this incredible challenge of, of breaking down this, this whole animal ex- and extracting as many nutrients as possible, moving them around the body as fast as possible, and then once the, uh, that prey is digested, you know, the intestine goes back to its normal thickness, the heart shrinks back down. Um, everything goes back to the way it was. And so, um, so, so scientists would love to understand this better because this could have all sorts of important implications for human health, you know. Um, uh, they, you know, snakes are, are, are, you know, are able to go through these remarkable changes in organ size or, or, uh, chemistry in the blood and so on, that might have implications for, for diabetes, for maybe even growing organs, just all sorts of, uh, potential clues might be there in how these particular, uh, sp- species just, you know, use this particular strategy to stay alive.

   4. CWChris Williamson24:37

      It's like being two animals in one.

   5. CZCarl Zimmer24:40

      It really is, yeah. Because, yeah, you just, you snap into this sort of eating mode, um, and then you go back to n- you know, not eating for weeks. And then hopefully, a few weeks later, you go snap back into eating mode again. And what's interesting is we think of snakes as being, uh, cold-blooded. Um, but the fact is that, um, they're, they're effectively warm-blooded when they are digesting something, because they're, they're use, uh, they're, they're, you know, using so much fuel, they're burning fuel. They're giving off heat as a byproduct of the work they're putting into digesting things so that, you know, you can, you can ... So if you use one of these sort of, you know, heat imaging, uh, cameras, you can see them glowing, uh, because of that. They're, they're, they're effectively warm-blooded just for that period of time. Um, the me- their metabolic rate is, um, roughly on par with, uh, that of a galloping horse. Um, now, you know, a racehorse might run for a couple minutes, and then we give him a big prize and say, "Congratulations." But these snakes, they're keeping up that metabolic rate for several days when they're just lying there. It's, it's astonishing.

5. 25:48 – 34:21

   Understanding Life for Fungi

   1. CZCarl Zimmer25:48

   2. CWChris Williamson25:49

      What about fungi and mushrooms and stuff? They must be an interesting case study for life.

   3. CZCarl Zimmer25:56

      Absolutely. Absolutely. You know, we, uh, you know, animals are fascinating and bizarre. So I just talked about snakes, I talked about tardigrades, but, you know, they're very close to us on the tree of life. And, um, you know, i- i- if you look further afield, you get to see, like, weirder things, um, things that don't even have bodies as we think of them. Um, so in the book, I write about slime molds, um, which are, they're not, they're not fungi, although they look kind of like fungi. They're sort of these giant single-celled blobby organisms that you can see, um, in the summer when you're walking around in the forest. Um, they have very evocative names. There's one species that's called dog's vomit because that's exactly what it looks like. You, you're walking along, you're like, "Wow, who puked here?" It's, it's an organism. It's alive. And, and th- that pool of vomit is actually one giant cell that is spreading out its tentacles across the forest floor and feeding on bacteria that it finds. So scientists love to study slime molds because you can take a little bit of it and dry it out, take it to your lab, and then splash some water on it, and it starts to grow. And those tentacles start to go, grow across a Petri dish. Um, and scientists have found that, um, you just need to give them a little oatmeal and they're very happy, um, because oatmeal flakes have, uh, bacteria growing on them. So they'll smell, essentially smell or taste the, uh, the oatmeal, and they'll just send their tentacles out across a Petri dish until they find it. Um, now what happens when you've got, like, three or four different clumps of oatmeal in a Petri dish, well, you know, the, the slime mold wants it all. But, you know, it doesn't wanna, like, build, like, a whole sheet of tentacles. That's a big waste of effort. So what it'll end up doing is it'll cr- it'll create this beautiful network of tentacles that's the shortest distance between those, uh, little clumps of oatmeal. It's solving a mathematical problem, um, in order to eat. Um, so scientists have all sorts of fun, uh, gi- running experiments with them. They put them in mazes. The, the slime molds send their tentacles through the mazes and solve them. Um, they, they do all sorts of, uh, uh, of these things. And, um, and again, this is something fundamental about life, um, you know, that in other words, that a slime mold is like us in that it takes in information about its surroundings and then it does something, it does something to sort of i- improve its chances of survival. You know, it respon- it behaves in a way that's better than random. Um, and so, you know, the scientists who study slime molds, they like to call this capacity intelligence. So you could say that, that intelligence is one of the hallmarks of life because everything from us to a slime mold has it. Um, and it's just easier to study in a slime mold in a Petri dish because you can just run experiment over experiment over experiment. Um, and they, you know, clearly you don't need a brain to be intelligent th- because these slime molds are literally solving math problems with no need of a brain.

   4. CWChris Williamson29:14

      Yeah, it seems like they've got intelligence, and if they do a maze, they must have memory. And if they're able to detect things around them, they must have some sort of senses of some kind.

   5. CZCarl Zimmer29:24

      Mm-hmm. Yeah, they seem to have, have all of that. (laughs) Uh, and it's not clear, it's not really clear how they've got it. (laughs) I mean, so for example, um, it could be that, that it- it's you just need some very simple strategies to, to tap into these kinds of intelligence. So, um, for example, um, slime molds, you know, they can detect where they've been. Um, in other words, like, i- if they've extended out a tentacle and they retract it back and then, uh, they're extending another tentacle and that crosses to where they were, they can kind of, they can kind of taste their own trail, and they don't like it. So they'll, they'll sort of move away from that place where they've been. So that is a way for them to not basically just keep going back to the same place over and over again. You know, if there's, like, a bad, you know, if there's some sort of toxin or, or s- or bright sunlight, which they hate, in a certain area, um, and they retract their tentacle, they're not gonna make that same mistake again, because they're like, "Oh, okay, that direction is bad. I've been there, it didn't work out, I'm gonna go over here." So that helps them to get around barriers to, um, you know, go, go through mazes and so on.

   6. CWChris Williamson30:39

      That's kind of like a rudimentary memory, but it's not sort of symbolic. It's not phenomenological, it's just leaving little trails here and there, and then you detect the trails again.What about-

   7. CZCarl Zimmer30:49

      Yeah. You're, you're sort of... You're making... Yeah. You're, you're... It's like an external memory.

   8. CWChris Williamson30:53

      Yeah.

   9. CZCarl Zimmer30:53

      So you don't need a hippocampus tucked away in your brain. You're just like, "Okay. I'm gonna, like, leave a little trail there. And I know that when I... If I reach that again, that reminds me, 'Oh, I don't want to be here.'"

   10. CWChris Williamson31:03

       Don't come back here. Yeah. Exactly. What about thanatology?

   11. CZCarl Zimmer31:08

       Yeah. So thanatology is, is this wonderful name for basically the science of death. Um, and, uh, it's... Uh, there, there's a small but dedicated group of scientists who, who study, uh, you know, the science of death, particularly, uh, there are, are scientists who are interested in how, how animals, um, respond to death, recognize, uh, that, you know, other animals are dead. Um, there's a particular sort of specialty of thanatology called primate thanatology, which is, um, which is particularly important, um, for us in terms of understanding where our own concepts of life and death came from. Um, so for example, you know, the, uh, Jane Goodall, um, the, the famous primatologist, you know, she spent years just sitting with chimpanzees, observing them day in, day out. And, um, she would just see things that you wouldn't see if, if you just came to visit them quickly. In one case sh- there was a, uh, a, a female, uh, chimpanzee with, with a baby. And, um, the baby wasn't looking well. And then the next day, it was obvious to Goodall that the baby was dead. And she could see that the, the mother was treating it differently now, um, was sort of just carrying it around, but sort of in this sort of strange way, just sort of, um, uh, holding it by a foot and things like that. And then, after a few days, eventually let it go, just it, uh, left it behind. And, you know, there, that's just, like, one observation but since then, in the decades since the 1960s, there have been more and more observations of, of primates and, and how they respond to the death of their, their, um, fellow members of their species. And th- and that, you know, is, is sort of h- uh, been leading to theories about, well, um, how, what are evolutionary roots of our concept of death? Um, you know, we... It's probably, you know, probably, you know, a chimpanzee recognizes... Chimpanzee doesn't say to itself, "Oh, this other chimpanzee is dead," but there is a confusion because, you know, they're, they're looking at something that, that the biological part of their brain, uh, is biological sensing part of their brain would say, "Well, this sh- is something that's alive. It's got a face. It's..." you know, and s- and so on. But, um, but it's not moving or it's b- arms are at a strange angle that living chimpanzees don't have. And it may be that that takes a while to, to, to overcome that, to override that. Um, so we can... You know, it's not... It takes quite a while in the fossil record for humans to really show our, you know, how, how sort of modern examples of recognizing death, you know, a, a, a funeral, for example. That's probably just in the past maybe 100,000 years that there are these rituals that humans performed, uh, in, in conjunction with death. So in the million years be- millions of years before that, they were probably behaving a lot more like the chimpanzees.

6. 34:21 – 40:16

   Other Forms of Life in the Universe

   1. CZCarl Zimmer34:21

   2. CWChris Williamson34:21

      Have you thought about what other types of life forms there might be out there in the universe? I watched a series on Netflix not long ago where they were talking about silicon-based life and all sorts of other exotic things. Do you look into this?

   3. CZCarl Zimmer34:36

      Yeah. There's actually, um, a small but really fascinating little thread of scientific research that goes back, um, 100 years of people trying to think of alternate life. Uh, sometimes they like to call it weird life. Um, uh, uh, because they, they call it weird because, you know, life as we know it, uh, on Earth is, is kinda boring, just in the sense that, um-

   4. CWChris Williamson35:02

      Familiar.

   5. CZCarl Zimmer35:03

      Uh, f- well, uh, boring in the sense that it's like, "Oh. Here's another species." Like, if you find a specie- a new species of bird, I can guarantee that it uses ATP. I can guarantee that it has its genes and code in DNA. And there are all these things I can guarantee it. Um, I can eith- I can even get down to, like, what is the genetic code that it uses to translate its genes into proteins. Like, just down to that level, there's not a lot of variety. So, so all the wonderful variation that we see and all these weird things I've been talking about, that's in a way kind of external. Like, at the, at the core, life on Earth is very similar. Now, that could be because, that could be because there's just one way to do it. There's just one way to do life. And, and that's what we see around us, and there's no other way to do it. Um, that, you know, the rules of, of matter and energy don't allow anything else. Or, that's just what happened to start here on Earth. Or, maybe there were two different kinds of life on Earth (clears throat) and our form won out and the other one's extinct. Um, we have no idea. And, and so, uh, you know, until we start to go to planets and moons and, and, and see whether they have life at all, and if they do, what form it takes, will we be able to say, you know, is, is silicon life possible? You know, chemically speaking, it, it, it, maybe it could be, um, you know, because some people have said, (coughs) well, you know, "What, what is it about DNA that, that's so important?" Well, it's important because it's a way to store information that you can then use to build other molecules. Um, well, there are... there could be ways of using silicon or some other, uh, materials-... essentially to work as genes. Um, and y- while we wait f- to finally get to other planets and moons to really, really look hard for life, um, some scientists are saying, "Well, who cares? Let's start. Let's get to work." And they're trying to build these systems in their labs. Um, and so you actually are seeing kind of alternatives to DNA that, that scientists are building and trying to figure out if they can make them work.

   6. CWChris Williamson37:24

      Was there anything else other than silicon?

   7. CZCarl Zimmer37:27

      Silicon is, is one of the main ones. Um, there's also an issue about, um, the, the matter of water. So that's another boring thing about life is that... uh, on Earth, is that it needs water. You know, we have water-

   8. CWChris Williamson37:42

      Is that because of the ATP?

   9. CZCarl Zimmer37:45

      Well, that's because, uh, the, the chemical reactions that, that make ATP possible and, uh, and lots of other chemical reactions, um, they need water to act as a solvent. Um, and so, you know, water interacts with proteins, um, to... uh, in all sorts of important ways, with our DNA as well. Um, and so, so we need, you know, we need water as a solvent, um, in, in our bodies. Um, you know, there are other solvents, you know, um, you know, kerosene. You know, like, (laughs) there are... We would not want to drink kerosene. Um, but maybe kerosene or, or, or, you know, liquid ethane or something like that, um, maybe that could be a solvent for some alternate form of life. And, you know, this, this actually is not, like, a totally, um, pure thought experiment, because, you know, there are some parts of the solar system, some moons where, um, there isn't liquid water, but there might be liquid ethane. Um, and so, you know, it's, it's actually really interesting to say, like, "Well, could there be life there?" You know, uh, or, or is it impossible for there to be life there, or would, might there be some bizarre, super cold ethane-based life, uh, out in our own solar system? Who knows?

   10. CWChris Williamson39:11

       One of the coolest things that I looked at, I'll try and find... I can't remember the name of the documentary. It was something like Different Alien Worlds: A Museum. It was just on YouTube. It was so good.

   11. CZCarl Zimmer39:22

       Mm-hmm.

   12. CWChris Williamson39:22

       And it sort of moved through all of these different pretend exhibits within a museum, and it explained how they all might come about. One of the things that that video said was the likelihood of finding really, really intelligent advanced civilizations that are water-based is essentially zero, and the reason is that in order to become technologically advanced, you need smithing. You need to be able to heat stuff up, you need to be able to create things in ways that allows you to get outside of your... And when you're underwater, that's really, really hard. So that was something that I hadn't considered as well, that you kind of have a, a cap on technological development for a civilization if it's water-based. And, um, Children of Ruin by Adrian Tchaikovsky, he's got these, um, these huge orbs that have got, uh, super intelligent octopuses in, octopi-

   13. CZCarl Zimmer40:09

       (laughs)

   14. CWChris Williamson40:10

       ... and, um, they're flying these massive orbs of water around, and, um, yeah, it's so f- it's such a funny idea.

7. 40:16 – 44:48

   Origins of Life on Earth

   1. CWChris Williamson40:16

      But what about, given that we've talked about alien life origins, what about origins of life on Earth?

   2. CZCarl Zimmer40:23

      So there again, you know, the definition of life is really important, because, uh, (clears throat) if you want to talk about when life began on Earth, you have to say, like, "Well, uh, th- this is the kind of thing that we would say was s- the original form of life."

   3. CWChris Williamson40:40

      That's the threshold we have crossed that now is defined as, yes.

   4. CZCarl Zimmer40:44

      Yeah. And, and so, you know, clearly, like, you know, a, a, a, a pool that's just full of, you know, loose bits of peptides and nucleotides is, and, and ATP, that's, that's not alive. That's, you know, that's a primordial soup. That is just a, a mixture of, of molecules that, you know, if they were to come together in a certain way, and could sustain themselves and reproduce, we might call them alive. Um, so then the big question is, how do you get from one to the other? Uh, and so in the book, I talk about, um, how, you know, scientists are, are, uh, trying to, uh, do experiments and going to extreme environments on Earth to, to address this question. Um, what's fascinating to me is that there are two really, um, well-th- thought-out, fleshed-out scenarios for how life might have started on Earth, uh, and they're completely mutually exclusive. So on the one hand, you have, uh, some people who are saying that life started on the surface. So like four billion years ago, there may have just been a few volcanic islands popping up through... uh, above the ocean surface, and you might have little ponds there, and in those ponds, as they, as they filled up with water and dried out, you would have a series of chemical reactions that might have actually produced RNA, and then might have been able to encapsulate the RNA into protocells. So there you got some people who say that's where life started. You have other people who say, "Nope, life started at the bottom of the ocean," um, at these, uh, vents in the, in the sea floor where you had these magnificent sort of mineral towers that form as, as hot mineral-laced water shoots up from the Earth's interior. And as that water and those chemicals get pushed through, uh, the, these chimneys, all sorts of interesting chemistry happens, and then you could actually start to... It could start to build up on itself and you start to produce the molecules that will eventually become our genes. You start to produce membranes that might eventually become our cell walls and so on. Um-So, you know, (clears throat) they might both be right. (laughs) Maybe one of them is right for Earth and one of them is right for a, a moon in orbit around Saturn. Um, it's hard, it's hard to say. Um, but you know, along the way, you know, the, these, uh, lines of research, they, they lead to amazing discoveries, um, very practical ones, uh, in some cases. So for example, right now in the pandemic, a really important way that scientists figure out, uh, you know, whether, you know, SARS-CoV-2 is infecting someone or what kind of SARS-CoV-2, what variant it is, they use a special kind of DNA sequencing called nanopore sequencing. Um, it's a pretty new, uh, technology. It's like the sequencer is like, is smaller than your iPhone, you plug it into your computer. Um, that was actually developed by people who were trying to understand the origin of life, because, uh, the, the, the fundamental way that it works is that DNA gets run through a little pore. Um, and that was something that people were thinking about when they were thinking, "Well, okay, when you have these protocells, they, they're going to need to get stuff in and out." We have very elaborate channels and, and various portals in our cells, but what, how would this all begin? Um, it couldn't be a perfectly sealed bubble. Stuff is got to get in and out. And someone was like, "Well, maybe they just have a simple pore. Maybe you could get a genetic molecule in and out." And then he said ... This was someone named David Deamer, uh, at University of California at Santa Cruz, he said, "Wait a minute. Like if I'm pulling DNA in and out through a pore, it's going to generate an electric, uh, current, a tiny,

8. 44:48 – 50:13

   Are Viruses Alive?

   1. CZCarl Zimmer44:48

      a tiny current, and we might be able to measure that." Um, and 30 years later, that's how we are, um ... one of the tools we're using in the pandemic.

   2. CWChris Williamson44:58

      That's sick. What about viruses then? Are viruses alive?

   3. CZCarl Zimmer45:01

      (laughs) Uh, again, it really depends on who you ask. I mean, I, one morning, um, I had a virologist email me and tell me, "Of course viruses are not alive, and any expert would tell you that." And then that afternoon, another one said, "Well, of course viruses are alive, and any expert will tell you that." Um, so, you know, as a science writer, as a sort of a chronicler of science, it's kind of a, a, an awkward position to be in, because, you know, people ask me questions as if there's some sort of, you know, clear-cut answers that I'm, I can refer to.

   4. CWChris Williamson45:36

      Like whose science do you go with? Yeah.

   5. CZCarl Zimmer45:39

      Well, you know, I mean, uh, science is, you know, d- debate and conflict is at the heart of science. There's nothing wrong with, with debates, you know, just as long as that they're, you know, meaningful ones. And this is a very meaningful one, because, um, it really forces us to think about, well, h- what are viruses in themselves? How do they work? And, you know, what do w- what does it take for something to be alive? And, and, you know, what do we even mean when we're using these, these terms? The thing about viruses is that (clears throat) if you line them up next to a cell, they're very different. They're not just w- much smaller than a cell, but, you know, a cell is full, I m- of ATP, like I mentioned, or fuel. There's just constant metabolism going on. Molecules are being built, other ones are being torn apart. They're pulling in things from their environment. It's this, just this, this, uh, you know, buzzing hive of activity. You look at a virus, um, just w- what scientists would call a virion, just a little thing floating around on its own. It's just a little protein shell with some genes inside, just wrapped up night, nice and tight. That's it. It's, it's not doing anything to keep itself going. What has to happen for a virus to replicate is that it has to fuse with a cell, and it goes in, and now the cell basically just starts treating the virus's genes like its own genes. The, uh, it starts making those viral proteins, those viral proteins then take over the cell and make the cell make new viruses, which then leave the cell to go infect other ones. So, you know, one of the architects of that NASA working definition of life was asked, "Well, if life is this chemically self-sustaining system capable of Darwinian evolution, um, are viruses alive?" And he said, "You know, according to this definition, no, they don't make the cut. You know, they don't, they can't sustain themselves." Um, other people say, "Well, you can't understand viruses without looking at them as being part of life." You know, viruses v- evolve. I mean, just look at the variants that are making our lives miserable. You know, the Delta variant didn't exist before October of last year. It evolved from earlier forms of the virus. Um, and, uh, so, and it, it follows all the same rules of evolution that animals or plants do. It's, it's a classic evolving thing. So, um, so the, so p- so people make a number of arguments about, um, how, how viruses really are alive based on a number of different ways of, of looking at it. Um, and, um, you know, it, it could be that there may actually be viruses that really blur the line and, and could make this even more interesting, because there are certain viruses that, (clears throat) you know, they have genes for things that are not just for making new viruses. You know, they have genes for building proteins, they have genes for photosynthesis. And they just carry those genes along, and then once they get inside the cell, they basically like tell the cell like, "Okay, here's what you're going to be doing now. You know, you're going to be photosynthesizing in a different way. You're going to be pho- capturing sunlight and, and turning that into molecules that are better for making viruses than for making more cells. So let's get to work."Um, and you know, it's... So there are ways in which, you know, viruses themselves may- may make this question even harder to answer.

   6. CWChris Williamson49:14

      I had a geneticist on a while ago talking about how we could engineer life to reach other space systems. And he was saying that one of the things Dr. David Sinclair's talking about some of this stuff in his longevity research lab in Harvard, where you have particular types of viruses that are turned on and turned off with antibiotics or with, uh, particular types of bacteria, I think. And then you could have... He had created this idea of a human who had, um, photosynthetic skin, and you'd need... I think he worked out in order to survive, you'd need about two tennis courts' worth of skin just laid out. Um, but he kind of imagined these green humans that wouldn't need food. You wouldn't need to carry all the food with you because you can just have your- your tennis court of wings stuck out to the sides, and then you can just get all of your sunlight and you could exist like that. So, yeah, it's, um... It's funny how all of this stuff comes together. So if... It

9. 50:13 – 57:10

   Discovering a Better Definition of Life

   1. CWChris Williamson50:13

      seems like there's quite a bit of chaos trying to work out what's going on here. Did you arrive or discover a better definition of life?

   2. CZCarl Zimmer50:22

      Uh, I think the most radical, uh, proposal, um, that I came across was, uh, from a philosopher named Carol Cleland at the University of Colorado, who said, "Don't try to define life. Definitions are pointless. You're wasting your time." And, you know, this really, like, bothers, uh, uh, a lot of scientists because they think that, um, that definitions are just part of what they do. Um, but in fact, um, you know, if you're not careful, you can get into s- sort of language traps. Um, so, for example, um, you think about o- uh, water. You know, think about an alchemist trying to define water for you in 1500. Uh, and alchemists did, and they would... And what they would do is they would, like, list off some characteristics it had. Like, well, water is something that's transparent, something that's wet, something that dissolves certain things. Like, that's my definition of water. Um, but then there were certain things that looked a lot like water, but were dissolving other things. Like it'd dissolve certain kinds of metal. So were they water? Well, they would actually say like, "Oh, we're gonna call this royal water." And then you'd have a problem when it got cold and this liquid water froze and became something called ice. Is this ice water? Well, strictly speaking, by the definition, no. Um, and so, you know, even Leonardo da Vinci writes in his journal about how frustrating it is that water just seems to be whatever you want it to be. It's just maddening. Um, so the definitions did not help in understanding. What- what was necessary was a few more centuries of- of research and the invention of chemistry as a science. Um, the way to talk about water is to talk about it in terms of with- with... In a theory, a theory of atoms and elements, of molecules, you know, and then you can talk about how molecules of two hydrogen atoms and one oxygen atom, and now you're really having a meaningful understanding of it. So, so what Carol Cleland argues is that what we really need is a theory of life, which we do not have yet. Um, there are people working on it, um, but, um, until we have that, i- if we just try... If we waste time coming up with hundreds more definitions of life and yelling at each other about it, that's time we could have spent moving towards a real theory of life.

   3. CWChris Williamson52:46

      Yeah, it's interesting thinking about that. I think... I think it was you that said it's like trying to describe red or effort. It's always described in terms of analogies. And then we have this sort of imperfect language so you just end up playing lexical Brazilian jiu-jitsu in an effort to try and work out the closest approximation of the thing that you mean. And then as soon as you make an analogy, the analogy is always slightly imperfect because, by definition, it isn't the thing you're talking about. It's a thing like the thing that you're talking about. And, um, yeah, I'm glad... I'm glad I don't work in the theory of life business, uh, frankly.

   4. CZCarl Zimmer53:23

      (laughs) Well, it's- it's- it's not for the faint of heart, that's for sure. And, you know, in- in the book, I actually write about, you know, some figures in history who- who really tried to go out there to life's edge, the title of the book, and you know, that edge where you're trying to figure out what divides life from non-life. And they've- they've flamed out, they've made terrible mistakes, and they've- they've gone down, you know, gone down into obscurity for- for coming up with crazy ideas that really just were- were completely off base. Um, you know, we- we- we- we tend to think of science as just nothing but a sort of a series of triumphs and- and a- a linear progression from one deep insight to the next. And, you know, that's not how science works. Science is- is full of- of branches in different directions, many of which just lead to complete failure. Um-

   5. CWChris Williamson54:19

      Who- who is one of those failures?

   6. CZCarl Zimmer54:21

      Well, I talk in the beginning of the book about a physicist named John Butler Burke, who, um... He was at Cambridge, and he was working at this lab where... In- in the early 1900s where, you know, the electron had just been discovered, you know. Quantum physics was- was being, uh, uncovered for the first time in places like this lab. Um, radioactivity was- was another thing that was fascinating people there because it could tell you about how atoms worked in this very strange way. And people were fascinated by the element radium, for example. And they- they would, you know... There would be dance performances where the dancers were- were dressed in radium clothing that glowed in the dark.Um, and so in this context, Burke, uh, thought, "Well, maybe, you know, ra- radioactivity is, is at the, at the... Maybe that's what life's about. You know, maybe radioactivity is the organizing principle behind life." And so he ran an experiment where he took some sterilized beef broth and he dropped some radium into it and then let it stay there overnight. And then he went into the lab the next day and he saw that a, a layer had formed on top of the broth. And so he scooped some of that out, put it in a, um, slide, looked at it under a microscope, and he convinced himself that he was seeing, um, microbes, um, t- teeny tiny structures that grew and became more complex over time that seemed to divide. (clears throat) And these were much smaller than microbes and, but they seemed to be alive to him, or at least to be right on the border. And so he named them radiobes after radioactivity, published a paper about them, wrote a book about them, was just the, the talk of the town. I mean, people were saying w- that, that Burke was important as Darwin. Uh, and this glory lasted for maybe a year (laughs) until some other scientist reran the experiment and showed that it was all, um, a fluke from bad chemistry. You know, if you used distilled water, this just didn't happen. Uh, and that was it. And he, for the rest of his life, uh, i- insisted that, um, that he, uh, uh, had been right and that radiobes really were there at the, at the, at that life's edge. Um, and, uh, you know, nobody knows who Burke is now. Um, in a, in a way, he was a real pioneer. You know, he actually used the term artificial life for the first time for what he had done, you know, trying to make life in a lab. He was trying to do it, um, but, uh, but we don't remember him because he was playing this very, very dangerous game.

   7. CWChris Williamson57:06

      Dangerous status job being a scientist. Life's Edge: The Search

10. 57:10 – 57:42

    Where to Find Carl

    1. CWChris Williamson57:10

       for What It Means to Be Alive will be linked in the show notes below. If people want to keep up to date with what you do, where should they go?

    2. CZCarl Zimmer57:17

       Uh, my website is carlzimmer.com, and I'm Carl Zimmer on Twitter.

    3. CWChris Williamson57:22

       I love it. Thanks, Carl. What's happening, people? Thank you very much for tuning in. If you enjoyed that episode, then press here for a selection of the best clips from the podcast over the last few weeks. And don't forget to subscribe. Peace.

Episode duration: 57:42