The Infinite Monkey Cage - What is Life?

Episode Date: July 20, 2020

Brian Cox and Robin Ince are joined by comedians Jo Brand and Ross Noble, alongside Nobel Prize winner Sir Paul Nurse and geneticist Prof Aoife McLysaght to ask the biggest question of all, what is life and how did it start? They look at the amazing feat of nature that has somehow created all of life from just four fundamental units of simple chemistry. From chickens to butterflies to yeast, we are all far more closely related then we think. But how did the spark of life occur and what has any of this got to do with Ewoks? Producer: Alexandra Feachem

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Hello, I'm Brian Cox. I'm Robin Ince and this is the Infinite Monkey Cage. We began the series asking how the universe will end and we're finishing the series by asking how life began. Basically what we're doing is we're running the whole thing backwards so there's a happy ending. And the problem is that, of course, Brian, though, there won't be a happy ending because he'll then explain

that we need to go further back and eventually we'll return to a time before light and matter when everything was crushed together at terrible heats. It's not my fault, is it? It's just the way the universe is. Physics always spoils everything, doesn't it? It does spoil things, physics. Today we are following in the footsteps of Erwin Schrodinger and asking the question which was the title of his influential book

first published in 1944, What Is Life? Joining us to discuss this profound question are four separate populations of interacting cells, at least one of which has won the Nobel Prize, and at least one of which we are very certain has not. And they are. Hello, my name is Ross Noble. And before COVID, I used to be a stand-up comedian. And now I'm simply an amateur chicken farmer who has a lot of chickens who are sick of me doing shows for them. And I think the most intriguing form of life on earth

is anything that can not only survive, but chooses to live in Romford. What a relief, by the way, Ross. We haven't had any letters of complaint this series, so thank you very much. That's all right. The final episode ensuring that many arrive with an Essex postmark. What a relief, by the way, Ross. We haven't had any letters of complaint this series, so thank you very much. That's all right. The people of Romford... Ensuring that many arrive with an Essex postmark.

The people of Romford cannot write. Oh, we're weighing up the mailbag. We're weighing the mailbag. I think I should get on, don't you? My name's Paul Nurse. I'm a researcher into genetics and cell biology. And today, I think the most intriguing form on life is definitely not a chicken. It's a brimstone yellow butterfly. And you'll understand that

maybe by the end of the programme. Hi, my name is Aoife MacLeys, and I'm a professor in genetics in Trinity College, Dublin, which incidentally is where Erwin Schrodinger delivered those What Is Life lectures that the book is based on. And I think the most intriguing form of life is the coronavirus because it's a tiny little thing at the edge of life and it has caused a huge disruption to the whole world. And I'm Jo Brand. I come from Romford. I am actually a full-time international model. I am actually a full-time international model. And I think the most intriguing form of life is a seahorse. And the reason I think they're great, there's three reasons.

First of all, in the morning they do a little sexy dance for their partner. And my husband's booked that in for tomorrow. I'm sure he's looking forward to it. Also, they don't have many predators, which is always very reassuring to know, isn't it? And also, the male of the species bears the burden of pregnancy. And that's obviously why there's that saying, don't put all your eggs in one seahorse. And I certainly wouldn't.

And this is our panel. And it was wonderful, by the way, to hear the first barking dog in the background. Every single week, we have at least... This never happens at the radio theatre. Radio theatre, one week it turned out it was the astronaut Chris Hadfield's dog as well. That was just as he got to a very pertinent point about life on the planet Earth, his dog entirely disagreed with him. So let's start off with the experts. Let's start off with Joe and Ross. So, Ross, the definition of life, how would

you define life as I suppose we've seen it on the planet earth I mean I subscribe to the uh the Keating theory that uh life is a roller coaster and you uh just have to ride it and um it's it's an interesting scientific theory because the thing is is a lot of people don't think it's been fully thought through because like that does the roller coaster does that represent existence? And then, because he hasn't factored in the queue. So is the queue itself, is that the sperm? And the carriage itself is the egg. But then he hasn't then factored in arriving at the park, the car park and stuff.

And his theory was shot down by the foresight theory. And that was that life was the name of the game, and I want to play the game with you. That's what he said. And the chaos of life, the chaos of life, he addressed the whole idea of the chaos of it by saying that life can be terribly tame

if you don't play the game with two. It's very confusing. Well, I do feel that we should go straight, because, Paul, you have got a Nobel Prize, so if anyone's going to be able to answer the problems of Bruce Forsyth's lyrics, it's probably going to be you. Maybe, not so sure. I think living things can be defined

because they have the ability to evolve by natural selection. That's Darwin's big idea, of course. And to do that, they have to be able to grow. They have to be able to reproduce. They have to have a hereditary system which exhibits variability. And if you put all that together and it all works, you have life. Now, Joe, do you agree with that or disagree i don't know because i'm from romford and um i i'm not gonna i'm not gonna mention it again ross you'll be pleased to know and so will everyone else i'm sure but um i like i like to try and go down the road of the most simple um definition uh possible so for me uh life life is anything that's not dead.

What's interesting, given Paul's definition, Aoife, you said in the introduction that you felt the coronavirus was the most interesting or certainly a well-known form of life at the moment. But given Paul's definition, viruses can't reproduce on their own. So are viruses, is it widely accepted that viruses are life forms? I think you said on the edge of life, those were your words. Yeah, I think people discuss them in that context a bit, you know, that they are a little, you might consider them a little ambiguous. I don't consider it ambiguous. I think they definitely are life, but they are an utterly scaled back,

minimalized form of life. They can't do most of the things. They are parasites. They can't do most of the things they need to replicate by themselves. They must be inside another living cell, which is why lockdown works in theory. You know, the virus can't move around by itself. It can only move around and survive inside people. But I think that also is true of

lots of other things. We can't, we're not totally self-sufficient either. We need inputs and the virus needs many, many more inputs than us. So I would still consider it alive, but I think it's on the edge of that definition. And my definition that I like to use, the simple definition I like to use, Joe likes simple definitions, is just that life is anything that's capable of self-replicating. So that's not as elegant as Paul's definition. And the problem with the definition... It's also, Aoife, it's not as simple as mine either, to be honest. I prefer yours. But the problem with the definition I just gave there is that it would include something like a computer virus because a computer virus can self-replicate. But we don't really think that's alive, obviously. But that's why the definition is clumsy. So it's simple, but it's clumsy.

That's why Paul's is a lot nicer. But yeah, coronavirus, it's the most pared back form of life, I think, that we can consider. Can I say something about viruses, too? Because I've been wrestling with it for over 50 years. I think that was a very nice explanation. I've come to the conclusion that they're both alive and dead. They're alive when they're inside the cell, and they're dead, a chemical substance, outside.

And I found that sort of satisfying. Like strawberries for the monkey cage aficionados. It's also a lovely segue for the fact that your new book, Paul, is initially inspired is not by erwin schrodinger's uh series of lectures which were they at trinity i'm trying to think uh you didn't listen to ifa's introduction did you where she actually said explicitly yeah that the lectures were given at trinity and you just he was he was doing something he was both listening and not listening he was texting. I'm always in a super position.

Just because it's topical, Paul, could you just describe how viruses reproduce and just characterise what a virus is? So a virus, it is fascinating because it is a chemical substance made of nucleic acid, which is the hereditary material, and it's coated usually in proteins. But it can't do anything unless it infects a cell, as you've already heard. When it gets inside the cell, the RNA, if it's an RNA virus, or the DNA if it's a DNA virus, is released.

And then it's copied. And after it's copied, it produces the proteins that are needed to make more of the DNA and RNA and also to cover the virus in that protein coat. When the cell gets filled up with all those viruses, then the cell births and infects other cells around it, which is why it is the minimalist life form, because it can only work in other life forms. And it's why I say it could be alive and dead, because when it's outside the cell, it's just like a chemical substance. But I think what Ify said was so important. We are all dependent upon other living things, all of us, just to a lesser or greater degree.

Viruses to the greatest degree. Actually, these algae, which can photosynthesize, that is used light for energy and also for making molecules, are probably the most independent form. But we all interact one with another. So the viruses are just at one extreme end, and we're a bit in the middle, and other microbes are at the other end.

Aoife, Paul talks about RNA, DNA. I thought it might be useful to have some definitions. RNA, DNA and their role. OK, so I think DNA is the one that most people are familiar with. This is one of these bits of science that's gone into popular culture. So deoxyribonucleic acid in its long form. And it is this famous double strand, double helix that is this beautiful image that people know about as well. So you've got these two strands that are twisting around each other. And each strand, you can think about it a bit like a twisted rope ladder.

And the rungs of the ladder are two pieces that have come together. And there's essentially four pieces in this thing. A, C, T, and G is what we denote them as. And in the DNA, you have the two pieces come together. It's always an A and a T and a C and a G. And they build this structure, this double helix. And that's the thing we're talking about there. So RNA is, DNA is deoxyribo and RNA is just ribonucleic acid. And essentially RNA is almost the same chemically, but it's a single strand instead of a double strand. And instead of being ACTG, it's ACUG. So one of them is slightly different. And they both can function as the hereditary material, the stuff that we pass on.

But for us, it's DNA that we have that gets passed on from parent to child. And then RNA will do some of the work inside the cell. So RNA for us ends up being the message. It shuttles the message from the center of the cell, the nucleus where all the DNA is sitting there. the centre of the cell, the nucleus where all the DNA is sitting there. And then the RNA shuttles the message from the DNA out into the main part of the cell where then the proteins get formed and they go ahead and do their jobs. Can I ask a very quick question? Is it still the case, because I was at university in the 19th century, is it still the case that you cannot inherit an acquired characteristic? Yes, that's true. So if you think

about your body, your reproductive cells are kept very separate from the rest of your body. So if you're female, your ovaries, if you're male, your testicles, and the equivalent in other life forms, and those are separate from the rest of your body. So if you have a mutation, for example, a mutation could occur in your skin due to UV exposure or it could occur in your lungs due to smoking and that mutation won't be inherited because it'll just be in that one part of your body which is separate from your reproductive organs.

Ross, I don't know how you feel about listening to Aoife and don't worry, I'll get straight to the extraterrestrials eventually. Don't you worry about that. But when you first hear both Aoife and Paul talking about just those four letters, A, C, T and G, and you go, so there's these four base proteins and the variety of life, I think it feels quite counter-instinctual to think just four base proteins. And then you look around, I mean, where you live and you're living on farmland and you see all these different forms of life and all of those chickens and all of those things.

And you think it's just four base proteins lead to all of the living things that we see. All of those things are possible. Yes. Let me give you a metaphor that might help. If you take the Morse code, it's just dots and dashes, right? Oh, yeah. However, you can write all the works of Shakespeare with that. You can turn through linear codes. They can be very simple. So the Morse code is like four bases. But the proteins that come from it are like the works of Shakespeare, hugely diverse. And if you put on top of that the fact that

the chemistry is very diverse, you have all the ingredients to make the huge diversity of life that you see around us. I mean, you know... No, no, no, but... Well, the two things. One, I'll be honest with you, at one point, I just, like, I'm in

no way OCD, but I'm just worried about that tangled rope ladder because all I could think about was Ewoks not being able to get to the shops. Ewoks? Oh, don't start. Last time I was on. Oh, God.

It always happens, doesn't it? Every time I see you, we talk about Ewoks. Yeah, because I've realised that you can basically boil all science down to Ewoks. You're absolutely right. But, Ross, I know you're only joking, but there is a serious enough problem of the tangling of that rope ladder.

Yeah, no, no, go on, talk about it. Every time a gene is going to be read, so as Paul said, you know, it needs to be read and transcribed into the message. You have to unwind the rope ladder a bit in the middle, which pushes these knots up and down on either side of it. And then this becomes a bit in the middle, which pushes these knots up and down on either side of it. And then this becomes a bit of a mess

that needs to be potentially fixed as well. So it does get tangled. It happens, that's all. That's why I was making that very important scientific point. That's why I made that point. We should tell everyone that Ross is in Australia and while we're recording this at three o'clock in the afternoon in the UK, it's currently midnight, and though the listeners can't see this,

Ross looks like someone who's a kind of local radio DJ who's rather annoyed that he's been bumped to the midnight slot. I very much appreciate you making excuses for me. I also have no basic scientific knowledge at all. And, you know, I'm dyslexic. So when you're talking about those letters, it's a bit like when I watch Countdown and everyone's trying to work out the word

and I'm just singing along to the clock. That is why all the forms of life you've made in your laboratory have been such fascinating shapes as well. I mean, I know I always take it back to science fiction, but from a movie point of view, I mean, you know, clearly, I mean, the correct answer is the film Splice, but which film, Adrian Brody, I mean, you know, he's unethical halfway through in that love scene,

but which film, have you seen it, Robin? No, I don't know who has. Let's just find out from the audience. Who's seen Splice? No. All right, well, perhaps you all need to go away and do some important research about DNA and then come back and then we'll talk when you're experts. That's all I'm saying.

Paul, as both of you have described this process, this central dogma, it seems extremely complex, elegant, as you said. But there's a lot of machinery involved in copying the genetic information and then turning it into some structure, you know, the life. So what do we know about what came first? Because it seems that it's all intertwined with each other and it's all necessary for any living thing on Earth to function. So how can we do, what do we know about how this came into being? Well, we don't really know anything, to be honest, but we can speculate. I think the most attractive hypotheses at the moment, and they are only hypotheses, is that the first life forms

were built on RNA. Now, RNA, as Ether explained to you, is not a duplex molecule. It's not a helix. It's single-stranded. And what that means is it can fold up in a variety of different ways. It's not a fixed structure like the double helix. And so that means there is the possibility for weak chemical activities to be encoded in the RNA molecule itself. It doesn't have to be translated into protein. And if it has weak chemical activities, then there is the possibility that it could actually replicate itself using that chemical activity. And therefore, you might have a solution to the problem that the RNA molecule can both be coding and also have chemical activity. And once you've got that,

maybe you can build something up, which is more complicated. Maybe the RNA could be found in little sort of lipid vesicles, say, where it's protected from the outside environment. And then eventually the RNA can perhaps drive the formation of the vesicles. Maybe you can get translation into protein. Perhaps it can all work. But we don't really know how it works at all, how that could happen. But RNA could be the starting material because it can code and at the same time have chemical activity. Aoife, will we always, I was just going to ask, is that idea of the first life on Earth, will it always have to be a hypothesis or conjecture because the actual physical evidence will not have remained? Or is it a possibility that we might one day be able to pinpoint that first moment?

I think it will always have to be a certain amount of speculation because there are, I think there's more than one possible way it could have happened. And it clearly did happen, but there's more than one possible way it could have happened. And so I think we can never 100% know which exact path the origin of life took. We can just talk about what's plausible and what's implausible. And so adding as well to what Paul was saying there, the way that the first life would have existed wouldn't be exactly like life is now, of course.

What we have now is too complex to have arisen quickly all in one go. So it would have gradually come about things like the RNA being both the message and the messenger and actually doing the activity as well is the best hypothesis we have for how the information storage came about. But there's also like what would have been there instead of a cell and all of these kinds of things. And Nick Lane in UCL has really nice ideas about how there could have been little pockets maybe in rocky surfaces that would have enclosed things sufficiently that the chemical interaction could have been enclosed. And I think we can think of these earlier stages as a bit like scaffolding. Like if you think like you're building some big fancy building and there are structures that are needed in order to get there, and then they're no longer relevant once the thing is built. And so we have these early features that were important in the origin of life that are no

longer relevant to life. So like these little dimples in rocks, if that's what they were. But they were the scaffolding that allowed life to build. Joe, I find, to me, there is something quite remarkable about the idea that, you know, perhaps for, as Paul was saying, perhaps for a billion years, this is a lifeless planet, you know, and then there is at some point somehow all of those things that possess no life whatsoever. It's almost, you know, hard to imagine that when we think of the Earth. There is this change. And now we get to the complexity we get. I just wonder how you feel about that stray dead planet, tiny pieces of life, these tiny. And then eventually we end up with this vivid variety yeah well i did some um kind of evolutionary stuff at uh university but i was at university

a long time ago and they were kind of teaching creationist stuff then so i no not really but um i just i just think it's very hard to get your head round that really kind of early stage of, because I don't know if our brains, especially not mine, are kind of tuned to sort of understand. I understand like the length of time and the infinite variety of chances there might have been. But at some point there was some sort of initial spark, wasn't there, that started it all. And I just cannot kind of get my head round how that would have happened. I just can't. Well, you know, Joe, you're in good company, can I just say.

I mean, really, we are only guessing. The ideas that Iter explained are fantastically interesting. Nick Lane here in london um proposed them they're really imaginative but they are just ideas because it's so difficult to know i mean it's 3.5 billion years ago for goodness sake i mean um what was it like then and some people think by the way that um it was it couldn't have taken place so quickly in a few hundred millions of years. And so it arrived, life arrived on a comet or an asteroid from somewhere else altogether where they had longer to produce.

I don't think that's likely myself, but some people think that. Do you think we'll ever sort of get to the stage in like thousands of years' time when people will kind of look back and kind of roar with laughter at what we all thought you know like we do at the flat earth society for example we do it all the time don't we we were just um you know mocking acquired characters from lamarck you were talking about it um you know what we think now will be um probably mocked, at least some of it, in 10 years. Are the comet theorists, are they an actual recognised sort of group of scientists

or are they basically just like nut jobs? No, they're not nuts. Francis Crick of crick and watson was one of the people who proposed it but it was a proposal of desperation not lunacy but desperation which the wonderful if you've never heard it before us it's called panspermia this wonderful kind of vision of but i suppose if the problem is that it still wouldn't answer anything would it if life comes from somewhere else you go well it still wouldn't answer anything, would it? If life comes from somewhere else, you go, well, it still doesn't say how it began. It just says this is the seed that arrived on planet Earth.

We're just displacing the problem to somewhere else. Yeah, and you're just shifting the problem elsewhere. And that was, I suppose, like Paul said, it's an argument born of desperation just because it's so difficult to explain. But I think I don't feel like it's so difficult to explain but um i think i don't feel like it's a necessary uh explanation i think a lot of we see a lot of weird improbable things happen even in um evolution after life evolved and joe was mentioning the idea of a spark you know maybe like i don't know if that's the way you were thinking but if you were thinking of a single spark maybe that started off life but um yes we don't that's rather concrete of me i know but no but we don't necessarily think have to think

necessarily even that life originated just once it maybe just um persisted once um long enough for us to be still here you know so that it could have been lots of types of life or some early things that could have potentially become life, but they didn't all survive. And maybe one of them out-competed the other and the others. And that's the beginning of the lineage that led to us and all the other beautiful diversity of life we have. Paul, this idea, we've talked about the origin of life. In some sense, although, as you say, it's way back three and a half billion years ago, we don't understand it. But I can kind of imagine that it's just chemistry, although very complex carbon chemistry. billion years later or so of huge collections of single cells that could interact together to not only just reproduce but ultimately to think which is us and what do we know about that process because to me that is even more remarkable that you could it's i mean i think

in your book you talk about cells just that you use with appropriately caveated the word purpose the purpose is just a copy base. That's what they do. They copy, but get them together in a big enough bag as it were, which is us. And they build spaceships and go to the moon. Well, I put in the book,

I put a white flag up. Really? I said, we'll solve this in the next, the century after this one. How on earth does this chemistry and physics give rise to creative thought i mean i i struggle with it i must admit completely struggle but isn't it interesting i mean these i mean all these what it is is of course our brains are made up of these

specialized cells and they make lots and lots of connections to other cells. They connect with each other with the spark of life, with electricity. And so there is a spark there, a vitalist spark. And somehow thought emerges. And can I say, regardless of what you read about neurobiology, we don't have a clue. I love it. I love the fact that you want to know about plasma. You've gone into all this. And then the fact that before you just said, we're just guessing. I love it. I love the fact that, like, I love the fact you've won a Nobel Prize and you've, like, gone into all this, like, it's just like, and then the fact that before you just said, we're just guessing. I love that. I love that so much. Wouldn't that be just brilliant? And it's so important.

Just if once, like, the Pope walked out on the balcony and went, ah, maybe, maybe not, you know? Love it. Maybe, maybe not, you know. Love it. It's a fascinating idea that something as complicated as us, you know, as Ross and Joe and all of us here, the information to build us is contained ultimately in a single cell. Yes. At some level.

It's amazing. It's utterly amazing. And, I mean, you know, you go to physics and you worry about dark matter and dark energy i mean and it it's really um really interesting or even is there something beyond the you know the higgs and is there a new physics and so on i i think of three things that are fundamental um for me in biology one i think we can tackle and the other two I'm not so sure. The first is how can a cell be organised with purpose? And that's this information and chemistry and physics. And I think in the next decades, maybe 100 years, we will solve that. I do think we'll solve that.

The second one is brains and thinking. We've already said that. And that I'm struggling with, because how do you get consciousness, creative thought? How do you connect physical matter, physics and chemistry, with self and with conscious thought? And that I wrestle with. And the third one we've already talked about, the origin of life. I think we're always going to be speculating there. The first of these is difficult but soluble. The other two I'm not so sure of. There's something that I find really fascinating as well about thoughts and ideas because we think of them as things that don't exist in a physical form. So you don't think of your thoughts at all as having any physical manifestation. Yet, if you get a brain injury,

you can lose memories, you can damage your thoughts and your memories in such a way. And so that's a physical injury to your brain that will somehow break your memories or break your ability to do certain things. So that tells you that there must be some physical form to those things as well, that even though they feel so beyond the physical. But, you know, this is the level that I start thinking about it. It's just going, wow, it's just I don't have answers, but I find it fascinating. And it contradicts our instincts, I think, and it contradicts our intuition. And that's part of what makes it really, really fascinating, but also really difficult. Well, if anyone would like to know less about this issue,

then they can listen to the episode we did last week about the brain, where over a period of about an hour and a half of recording, we managed to fail to answer question one and left the other 22 questions well alone. Sorry, Ross. I was just going to ask then. I know this is, so what what are we going to get to first and so like because obviously ultimately you know all of these things lead to you know the rise of the machines killing us all so um like like all science

basically that's what it's there for let's just agree on that now there's no question of that so which is going to happen first then? Are there machines replicating human thought and then using that in order to rise up? Or are we going to get to that first? Or are we going to get to actually being able to build the brain that then becomes thought, that then that rises up? What are we looking at here? Aoife, which dystopia do you want to go for?

I think it's probably easier to train machines to do something that looks like human thought. It isn't quite, but it simulates it quite well than it is to make anything like a brain. We can't even make a cell from, a single cell from first principles. If you heard a few years ago, there was this big news splash where they said they had, you know, created life, this thing they called Cynthia, but they had actually just synthesized a really long strand of DNA and inserted it into a cell that they had removed the other DNA from. So this thing of actually building a cell is really, really difficult. And this is what Paul's referring to as well, I think, in how do you create this thing with purpose and that's organised.

So I think that's probably a more difficult problem than teaching a machine to do something that looks like thought, but for the machine to really think independently, that we have to define at what point we agree it is independent. I think that over these hundreds of thousands of years, intellectual thought is really cranking up and speeding up, isn't it? And I think things will happen much more quickly. I was a big fan of Hal in 2001. And so I think that's going to happen at some point. But if you look at the development of creatures, I just sort of over hundreds of thousands of years, I saw a brilliant thing.

I'm sorry, everyone. It was on Mumsnet. But someone wrote in about their daughter and they were worried about her because she was in a swimming group and she was being bullied because she was stuck in one swimming group and not good enough to go up to the next group. stuck in one swimming group and not uh good enough to go up to the next group and i i think the names of this swimming these swimming groups were just a perfect representation of development evolutionary development i've never heard anything like it so the top group was called dolphins and then it went tadpoles, plankton and bacteria. And I was like, who came up with that? That is so damning. Also,

if you were in bacteria, you'd go, I'll show you bacteria. Oh, yeah. Oh, once the dolphins get into this pool, they're going to find there's very little pure water left. Were the bacteria kids, were they just the ones that hadn't, they're not even good enough to get out of the foot bath in the changing rooms.

They're just standing there like, come on. I felt sorry for plankton as well. It's not exactly moving on, is it, in many ways? Joe, what you might like to do is start your own group. Just get a pen and just above dolphins write Japanese whaling fleet. Yeah. Now, we always ask an audience question, but this was inspired this week by the last few lines of Paul's book,

which I wanted to read to you. I think they're a tremendous reflection on life, life on Earth. And this is what Paul writes. He says, as far as we know, we humans are the only life forms who can see this deep connectivity and reflect on what it might all mean. That gives us a special responsibility for life on this planet, made up as it is by our relatives, some close, some more distant. We need to care about it. We need to care for it. we need to care for it, and to do that we need to understand it. I think it's a beautiful summary of what we've talked

about. So that led us to the audience question, which is what is your best reason for not destroying all life on planet Earth? Caitlin says, I'm still waiting for that hoodie I bought from Wish two years ago to turn up. I'd hate to miss that. Elaine said, to allow Robin and his cardigans to continue evolving, they are very nearly sentient and just need a bit longer. And, of course, David Attenborough. Andrew would like to say, because I've just got my Wi-Fi working properly. This is a good one from Mike Craig.

He says, because we never find out how how 2020 ends yeah i'm not sure we want to what about you we thought we'd ask you the same question so um maybe start with joe um what what is the best reason for not destroying all life on planet earth well i've got three reasons and they are decent people who give a toss laughing and curly whirlies ross um well i mean put it this way right forget that question just for a second i just want to i just want to say this i'm gonna get this is more important right because are you a politician you're a politician answer the question answer politician. Answer the question.

Answer the question. Moving forward, moving forward, I think it's very important. No, basically, this tonight has changed... It's genuinely changed my life, right? Because what I'm going to do is I'm going to get a copy of Paul's book, right? And the next... Honestly, this has changed my life. I'm going to get a copy of Paul's book, right?

I will read it. Sorry, I'll have a go at reading it and the next time my wife turns to me and goes why haven't you put the bins out i'm gonna go read this paul best reason for not destroying all life on the planet Earth? Well, I said it in those last sentences. They're all our relatives and we're all mutually dependent. I think that's pretty two good reasons. And Aoife?

Well, I think if we did have that devastating thing that all life was destroyed, we would never get the same again. It could be new life again, but every form of life we have and every individual is a total one-off never to be repeated so you lose a lot but this must never even though this seems democratic what we've done this must never be put to a democratic vote oh they actually voted for destroying all life on the planet i really wasn't expecting that at all um Thank you so much to our wonderful panel, Paul Nurse, Aoife MacLysette, Joe Brown and Ross Noble. And this is the end of this series.

It started as a six-episode series, but then extended to nine due to the speed of the expansion of the universe, I'm told. I'll just stop you there. That's not true. Because the density of the universe falls as space expands. So, following your logic, we should have done fewer episodes if we'd wanted to remain physically consistent. One, very rarely do I wish to remain physically consistent.

In our partnership, you are the physically consistent one. 12 years hasn't changed a bit. Me, I've gone with the entropy and the ageing process. Also, physical consistency could affect the number of episodes we get for the next series. So, anyway, we will be back this winter for series 23 of our increasingly physically inconsistent voyage through this increasingly absurd universe in our infinite cage. And that, of course, will be when the days have also got physically darker

and possibly metaphorically darker as well. There you go. Downbeat ending, but that's entropy. Goodbye. That's what happens if you stick us so close to thought for the day. Done that nice again. Hi, I'm Joe Wicks and I'm just popping up to tell you about my brand new podcast with BBC Radio 4. It's extraordinary. It almost turbo charges you.

I'm really interested in the links between physical and mental health and what kind of ordinary everyday activities people do to keep on top of things. I keep fit because it's relaxing, because it absolutely relaxes my mind. And that's so important. So in this podcast, I'm having a chat with some of my favourite people to find out their tips and tricks to staying healthy and happy. For me, it's a full body experience and it's a total game changer. I think you're going to love it. Hit subscribe on the Joe Wicks podcast on BBC Sounds. Let's do this. Hit subscribe on the Joe Wicks podcast on BBC Sounds. Let's do this.

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