Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas - 188 | Arik Kershenbaum on What Aliens Will Be Like

Episode Date: March 14, 2022

If extraterrestrial life is out there — not just microbial slime, but big, complex, macroscopic organisms — what will they be like? Movies have trained us to think that they won't be that different at all; they'll even drink and play music at the same cafes that humans frequent. A bit of imagination, however, makes us wonder whether they won't be completely alien — we have zero data about what extraterrestrial biology could be like, so it makes sense to keep an open mind. Arik Kershenbaum argues for a judicious middle ground. He points to constraints from physics and chemistry, as well as the tendency of evolution to converge toward successful designs, as reasons to think that biologically complex aliens won't be utterly different from us after all. Support Mindscape on Patreon. Arik Kershenbaum received his Ph.D. in Evolutionary Biology and Ecology from the University of Haifa. He is currently College Lecturer and Director of Studies at Girton College, University of Cambridge. He is the author of The Zoologist's Guide to the Galaxy: What Animals on Earth Reveal About Aliens — and Ourselves. Web site Cambridge web page Google Scholar publications Amazon author page Twitter

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best new audiobooks available on Audible. It's the book club for your ears. Listen to Earsay, the Audible and IHeart Audio Club on the IHeart Radio app or wherever you get your podcasts. Hello everyone. Welcome to the Mindscape podcast. I'm your host, Sean Carroll. In various conversations, both here on the podcast and elsewhere out there and what you might think of as the real world, I've noticed that the topic of extraterrestrial life, life on other planets elsewhere, let's just say in our galaxy, is one that engenders very strong emotional reactions. People feel very strongly about this topic, about whether or not such life exists, about whether or whether or not it will be technologically advanced, whether it will be friendly,

whether it will be like us or something completely different, which when you think about it is funny. I mean, why should you have such emotional reactions about something about which we know so little, about which there is so little data? I think that it's okay, I mean, as a good Baysian, you're going. to have priors about the likelihood of certain things, but you shouldn't be so confident, one way or the other. I have my own beliefs. You know, I think that it's actually unlikely that in our galaxy there are other very advanced technological civilizations out there. If I didn't

know anything, if I didn't have any data at all, I would think that might be very likely. There are a lot of planets out there, after all. But if there were technologically advanced civilizations, it would be very easy to have noticed them already, and we haven't. Now, maybe they're hiding or whatever perfectly possible, but it's just easiest to imagine they're just not there. But again, we should be open-minded. I could be completely wrong about this. When it comes to what life is going to be like, again, we know very little. It's certainly very plausible that life is ubiquitous, but it's just single-celled or extremely primitive in all sorts of ways. If life does become complicated, if you get eukaryotic or

the equivalent, multicellular life in a variety of different configurations, what are those organisms going to be like? Are they going to be somehow like humans? Are they going to be Star Trek aliens that have humans but rubber faces? Or will it be something completely different? I've generally been on the side of thinking life will be something completely different just because, again, what are our imagination supposed to tell us about these things? It's just too easy to be swayed by our experience with life here on Earth better, I would think, to be very, very open-minded about the possibilities for something growing up somewhere completely different. But again, it's important to listen to the views on the other side. So on today's podcast,

we have Ari Kirshenbaum, who's a zoologist at the University of Cambridge in the UK. Usually he studies how various kinds of animals communicate to their versions of language and so forth. But he's written a fun new book, The Zoologists Guide to the Galaxy. So what he's doing is using his zoology training and general biological knowledge to imagine what life on other planets, especially advanced life, might really be like. And he takes the opinion, again, not very strongly. He's being very reasonable, but he wants to raise the possibility that, despite our complete lack of knowledge and the openness of the possibilities, we have learned a little bit from how evolution works here on Earth to say that maybe life will be kind of like

us. The basic idea being that even though we only have life on Earth, life on Earth is complicated, and there's a lot of it, a lot of different niches, a lot of different competitions for survival and under different circumstances. And what we see over and over again is evolutionary convergence to certain forms. There are also constraints from physics and biology and energetics and chemistry that make certain configurations more plausible and more rewarding and more reproductively successful. There are reasons why organisms tend to be bilaterally symmetric, have four legs very often, the advanced ones. be a certain size, have a brain, etc.

So, Ayrich uses these kinds of considerations to say, you know, maybe it's more likely than not that the aliens are going to be somewhat like us. Again, it's not going to be Star Trek, okay, sorry about that. It's not going to be Vulcans. It's not just going to be the ears. It's going to be more different than that. But maybe they won't be that different. And we even go in a little bit to talking about how aliens could communicate

in their social organizations and whether or not they will be friendly. And again, he tries to at least put the idea into your head that there's, some optimism that aliens will not be completely 100% alien after all. I think it's very important stuff to think about because I still want to find the aliens out there and I hope that they're friendly, even though I suspect they're not out there and I worry very much about them not being friendly. So let's go. Ari Kersh & Bowen, welcome to the Mindscape podcast.

Well, thanks for inviting me. Let me start with the classic rewind the tape thought experiment, right? This is Stephen Jay Gould, I think, famously said that if you had started evolution again back from the beginning and let it go, there's enough kind of random fluctuations that would something, that we would end up with something that looked completely different than what we have in the ecosystem right now. So yes or no, is that, is that true? Well, it's, it's the kind of question that's, that's, I don't know, I don't think people really, really take it quite the way that it was, that it was meant that he that he initially meant. Obviously things are going to be different. So much of Earth, history has been dependent on contingencies and random chances and asteroid strikes and things like that. The idea that things will be exactly the same, it clearly isn't right. But the question is, are we going to get some of the same processes, some of the same

results that we did in real life? And it seems the answer's got to be yes, right? We've got to have the same kind of stuff. There's a whole bunch of reasons why that is the case, why we would expect that if evolution was to start again and go through everything again, we would still expect to see, you know, four-legged creatures and six-legged creatures and eight-legged creatures and things like that. And the main reason, the sort of simple reason,

is that a lot of the solutions that life finds or that life can use are really, really heavily constrained. And there's very little that's more heavily constrained than, constrained by physics, right? So legs, right, legs. How do you move on a solid surface? You've got to have some friction, otherwise you can't exert a force. You really don't want to have much friction because you don't want to use too much energy. So legs just seem to be this great solution. And they've evolved so many times because there aren't a whole load of ways to do it. Now, when you come to legs, it's an interesting, legs are an interesting example because there are actually a few different kinds of legs on earth. And if you look at starfish, for instance, they have really,

really, really interesting legs. They're not solid legs. They're not even fixed legs, right? There are lots of little holes in their in their shell and they and they exude part of their insides out to form a little sort of stubby leg and they can have hundreds of these legs. So there are other solutions to what we recognize as legs. But you notice that the kinds of jointed legs, that have become really successful in insects and the crustaceans and the vertebrates, legs that you can use as a lever. You can pull one part of the leg with a muscle. They're just much more efficient.

Now, given that these are really, really efficient, really effective solutions, if we were to rerun evolution again, would they occur? I suppose they might not by chance, but given enough time, they're so advantageous. It's going to happen. Well, we're ultimately going to try to extend this reasoning to think about what aliens are going to look like, but life is going to look like in other planets. But we're constrained by only having the one data point here, right, here on Earth. So is there some extent to which different periods of time in biological history count as different data points? Like, can we think about what niches were filled and with what solutions back in the dinosaur age and in other ages?

and then sort of got wiped out and learned that, in fact, things do find similar solutions? Well, the first thing I've got to say, I've got to say that when we find life on other planets, and we will, and we'll find life soon, it's going to be slime, right? It's just going to be like bacterial slime. The vast majority of planets that we discover with life will be very simple life. And you just need to look at Earth's evolutionary history, how long it took the complex life to evolve, realize if you were to choose a point at random in Earth's history,

you'd find a lot of green slime around and not much else. So, yeah, looking back at Earth's history, you can see that there were periods when, well, life was simple. What I'll call simple is, of course, incredibly complex. These single-celled organisms are actually unbelievably complex, and their biochemistry is incredibly complex. The genetics is incredibly complex.

but compared to life on earth today and specifically compared to the diversity of the ecosystem today, it was a very, very, very simple world. But to come back to your question, can we use these different eras to treat them almost independently and to say, well, this gives us a clue about one aspect of how life evolves, this gives us a clue to another. can to an extent. I think that there is an argument there. And that's because, I'm sure we'll come back to this again and again, what drives evolution. What drives evolution is ecosystems. You don't think of this. Most people don't think of this. Most people don't realize this.

People think evolution is like survival of the fittest and stuff like that, which it is. But fitness and difference in fitness only comes about because of complex ecosystems. Sure, you can have a world, you know, that it's a bit hotter here and a bit colder here. And here you get you get some physical differences in different place. You get adaptation to physical environment. But pretty much all the diversity we see on Earth is because of interaction with other organisms. And so the more complex an ecosystem becomes, that's when you start seeing these really complex innovations. And you won't see them in a simple ecosystem.

So in other words, there were flying dinosaurs in some sense. Can we think about that as sort of a prediction you could have made ahead of time? You say, well, you know, it's going to be a lot of dinosaurs. It'll be a lot of different kinds of life. There's a niche out there for flying creatures. And chances are life will find a way to make that happen. Or is that too simplistic? Well, flight is obviously a really useful thing. Assuming, you know, assuming that you live on a planet that's a solid surface and probably a gaseous atmosphere. Don't forget, flying is really, really common in the ocean, right? Fish fly. There's no real physical difference between a fish flying and a bird flying except that the fish has as close to a neutral buoyancy. So if it stops swimming, it won't fall and get squashed on the ground. But actually, aerodynamically, hydrodynamically, they're very similar processes. But let's talk about gas atmospheres. Yeah, it's really useful to be able to move above the ground. And we've seen flight evolve on Earth at least four times, at least four times. All four times are there in groups that have jointed limbs. So birds, bats,

terosaurs, extinct terosaurs, and of course, insects. But you've got to be able to be a able to have quite a you've got to be able to flap your wings essentially all four evolved with wings that's not to say there's no other way to fly but all four times on earth they evolved with wings and with to some extent flapping wings because you need support you know you need you need levers that you can that you can attach muscles to and make your wings flap so so to some extent you could predict that if flight is going to evolve again it will evolve in an organism with a skeleton and either inside or outside. I wouldn't expect jellyfish to fly,

and I wouldn't expect worms to fly, for instance. So there are constraints like that. Whether it would specifically be those dinosaurs that evolved into all the birds that we have today, that's kind of a harder prediction to make. Okay, fair enough. Good, enough for Earth. There's Earth sussed.

We'd like to move on to other planets now. You've already made this dramatic claim, and I've let me get away with it, but let's dig into it, but we're going to find life, we're going to find life soon. I hope that's true, but I'm certainly far from convinced that's true. I mean, certainly it would fit the data if life on Earth was the only life in the observable universe, right? So what gives you the conviction that we're going to find it soon? I'm not sure that it would fit the data.

And certainly, certainly when we look at the estimates, current estimates of how many Earth-like planets there are in the galaxy. I'm not even talking about planets at all. I'm just talking about Earth-like planets. You know, current estimates are between 10 and 40 billion. Now, that's a lot of opportunities for life to arise. And another point that people forget, which is worth making, which is that Earth is really the environment of Earth was not particularly unusual, and not particularly unusual chemically,

or in terms of the other environmental conditions. So we've got no reason to believe that the origin of life on Earth was due to some set of very unusual circumstances. People forget how common water is in the universe. I mean, water is really common in the universe. So it's not really all that surprising that we've got a life that's based on water. So I think that the numbers gain really strongly, and indicates that what's happening on Earth was not something,

was not something exceptional. The optimism of finding life on other planets in the near future, yeah, you could probably argue, well, okay, there's life on other planets, but it's so rare that we're going to struggle to find it. And I tend to lean towards the more optimistic side. Origin of Life is not my, not my field. Although, of course, I, you know, I listen in as I pass by rooms in the corridor. But, but, you know, we've made a lot of progress about thinking about different ways that reproducing molecules could arise.

And I think that the sort of consensus at the moment is that this is not an unusual thing. This is not something that's outrageous or outrageously unlikely. So I think when you put those two things together, I don't think it's an unreasonable hyperbolemen. health is that life's going to be widespread. When people turn to telehealth for weight loss, they're looking for real support. That's why more people are choosing orderly meds.com. Orderly meds connects you with real doctors and access to proven GLU-1 medications like semaglutide and terseptatide.

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Visit Farmhouse Fresh.com and use code radio for a free starter routine with any purchase. I know, I certainly agree with that. And I don't want to dwell on this, because this is not exactly, as you said, your area we have talked with people whose area it is. But there's a lot of planets out there that are Earth-like. I get that.

I just think that we have no idea right now what the chances are that any one planet would develop life. Maybe it's 0.9. Maybe it's 10 to the minus 100. I just don't know. But let's imagine that it happens. So there's slime all over the place. we have to quickly jump because we want to get to the more advanced life.

So maybe say something about this bottleneck that appears to be there going from single-cellular organisms to multicellular organisms. Yeah. And of course, life on earth existed for, well, most of its history without the existence of complex multicellular organisms. And when they did arise, it took a while, right? Well, we don't know, of course, but it probably took a couple hundred million years before multicellular life really became something like what we recognize now. And one of the interesting hypotheses, and it's really just a hypothesis, but it's a very appealing one, is that these couple hundred million years, 100 million years of early multicellular life

in what we call the pre-Cambrian. So before we really have a lot of fossils, these were very simple ecosystems, very simple ecosystems. So you had detritus feeders, you had organisms that fed on, so organisms fed on dead organic material, perhaps. We know there were some grazing going on. We know that there were organisms that ate algae and things like that. We do have some fossils of that. But essentially, it appears to have been a world without much in the way of predation. as we understand it now.

And the Cambrian explosion, so this event 540 million years ago, where all of a sudden we see fossils of all kinds of, basically of all the forms of life that we see now, or the progenitors of all the different major branches of life we see now, and a lot that have gone extinct, of course. These suddenly appeared. And people speculate, you know, was this because of chemical change in the environment

or some kind of temperature change, and no doubt the trigger was one of those. But that's not why that diversity exploded. That diversity exploded because new niches became available, because new interactions became available, because organisms had to live their lives differently. They had to run away when someone was coming to eat them. They had to burrow in the sand. they had to grow a shell so that so that they wouldn't be eaten. They had to grow teeth so that they could eat other organisms, eyes so that they could find food and so on. And so really that all of these adaptations,

the spikes and the shells and the huge complexity of the Cambrian the Cambrian fossils derives from the complexity of those interactions between the organisms. You don't evolve these things for the sake of it. You follow these things that they give you an advantage. Yeah, so that really was the big, that was the big transition. Now, whether that's an inevitable transition, seems likely. Okay.

I mean, people have certainly made the case that how long can a world without predation exist? That is essentially an unstable. It's an unstable system, you know, unstable, but for a couple hundred million years is pretty stable. But sooner or later, someone's going to take a bite out of someone else. and then all bets are off. I like that. I think that'll be the motto for the podcast. Sooner or later,

someone's going to take a bite out of someone else, then all bets are off. So, I mean, it's interesting because it's clear that in both cases, the transition from non-life to life and from single-cell organisms to multi-cell organisms, there always was this possibility, this prospect of greater complexity and all these niches being filled,

but it did take a while for it to catch on. But I guess both the existence here on Earth of both transitions gives us hope or the idea that ultimately life will get there, right? I mean that if you give it enough time, enough space, life is going to find these interesting, complex ways to thrive. Yeah, the sort of the rationale behind that. And I think this is a fairly well-supported idea. The rationale behind that is that natural selection, while not being a very efficient process, very inefficient process, but it is quite a thorough process. So if a niche is available, given enough time, you would expect an organism to discover that niche.

And that's why an unstable system, such as one where no one eats anyone else, seems unlikely to be able to persist in the long term, because really sooner or later there will be some kind of, some kind of mutation, some kind of sequence of events that leads organisms rather than to making their own food or eating what they find on the ground to exploit other organisms. And that's really a feature of natural selection

that it does tend to find those niches if they are available. Yeah. Speaking of which, the last big transition that I just want to get on the table is intelligent life. What can we say about the idea of the inevitability from a natural selection point of view that once life becomes complex enough to be multicellular, it will discover the mechanism of intelligence, of, you know, of gathering information about the world and processing it in a non-trivial way? Well, I'm going to, I'm going to make a stand here and say that I don't know what you mean by intelligence, but animals have been intelligent ever since they've existed. Okay. Right. So 800 million years, there's been intelligence.

Intelligence really is an ability to, I don't think we can come up with any, any robust definition, other than an ability to interpret the environment. And I suppose you could say to integrate different sensory inputs. So if you just respond reflexively to one input, you might not call that intelligence. But essentially, animals have been intelligent since they've existed. When we talk about intelligence, when people talk about intelligence, particularly when people talk about alien intelligence, they tend to mean intelligence like us. And even that is not a very easy thing to pin down. How long has there been intelligence like us? Hmm. So really the, the, the drive,

as we understand it now, and this is still a field of active research and quite contentious, really, as we understand now, human intelligence, the sort of thing that we would look at in an alien and say, oh, yeah, they're intelligent like us, is probably driven almost exclusively by social requirements. So we are intelligent because we had complex societies. Our ancestors lived in complex societies. And you know, they needed to keep track of who, uh, who worked with them yesterday and who, who annoyed them yet the day before yesterday and who they should, who they should cooperate with now to to form an alliance against this one. And like this kind of complex social processing seems to be, um, something different from the intelligence

that you see in a lot of other species. Any species can be trained, um, using, very simple, very simple training techniques to perform clever tasks. Yeah. Clever stuff. Yeah, all animals can do that. Chickens can do that. Bees can do that. You can use,

you can use operant conditioning to train just about anything to do just about anything. But this kind of social intelligence seems to be much rarer. And I think that that's, so that would seem to be, I'm not sure that it's a phase transition. I think it feels like a phase transition. feels like a phase transition to us because of the way we've altered the world. Yeah. Rather than because of the nature of the intelligence itself, there are, of course, other

intelligent social animals on the planet, many of whom have been around for a lot longer than us. They just haven't done the damage that we've done. And so you might not have recognized that as being a phase transition. I guess that, it raises another question. that I hadn't thought about explicitly, but I completely am on your train as far as we've been intelligent as long as there have been animals,

but there's some kind of intelligence that we have in mind. Specifically, when we're thinking about aliens, we're gonna ask about the ability to develop technology, right? That's something that we're gonna care a lot about. I mean, what is the lesson we learn from the fact that here on Earth there are different species that are intelligent in different ways? And yet human beings are the ones

who came up with the ability to build machines and so forth. And the standard answer, there is a standard answer. The standard answer is language. Of course, that's cop-out answer because why did humans evolve language? Hasn't actually answered any question. But there does seem to be, our technological ability does seem to be linked to language. And you could imagine, you could argue persuasively, I think, that an intelligent technological alien civilization must have a language.

You're going to build a spaceship. You've got to say to someone, hey, pass me the screwdriver, whatever. You've got to have some way of communicating. So language seems to be very closely, very closely involved in this. The trouble is we don't really know why language evolved. We don't have a really good handle on what it was, what happened that caused this very, this really was phase transition.

From whatever our ancestors, however they communicated, and I'm sure they communicated well, but that jumped to the ability to convey an unlimited number of concepts and just to invent concepts and convey them. We don't have a good idea how that happened. But I think that's got to happen for a truly technological civilization to arise. And just to be clear, when you say language

means something much more specific and communication. All animals communicate, but do you mean something more symbolic and abstract and the ability to generate all sorts of different ideas? Yeah, the definition of languages is also really contentious and different people from different disciplines will give you different definitions. I've got a very simple definition. It's the ability to communicate an unlimited number of concepts. So we know from studying animal communication, sometimes very complex, it's never anywhere close, never close to conveying an unlimited number of concepts. That really does seem to be a purely human thing.

How that ties into abstract concepts, how that ties into predicting the future and imagining the future. Different people have a lot to say about this. To what extent is our ability to imagine ourselves in the future? to what extent is that really tied to our language? People used to think this was essential. If you don't have a language, you can't make that kind of mental leap. There are some animals that appear to have that ability to a greater or lesser extent, but certainly none of them have languages, as I would define it.

Yeah, we had a previous podcast guest, Malcolm McGuiver, who studies the transition from life in the water to life on land, And he thinks that that was actually the first transition that started animals on the road to imagining the future long before there was language. But that's an interesting connection that I hadn't thought of myself. So what I want to ask you is, again, to be very, very specific because you just made the claim that only human beings have this ability to generate infinite number of concepts through language. So we're making a claim about the intelligence of, you know, dolphins and octopuses and. and so forth, they can have, in some sense, very high intelligence, and they talk in complicated ways, but without this sort of infinite possibility space the language gives us. And this is your area,

so this is something I can ask. Yeah, that's right. And that's, that is what we think at the moment. Obviously, we could be surprised in the future. I don't think so. There are a number of reasons to think that that's that's not the case and one of the most important reasons that we've got to put on the table right at the beginning is that you know animals are not trying to be human animals are not evolving so that they can become more like human and it's really easy I think to slip into this idea well dolphins are intelligent right and dolphins are cute and they communicate a lot so why shouldn't they have language like us well why should they have language like us actually You know, in what way are we the pinnacle of what evolution should be doing?

We're clearly not. Dolphins have a communication system that suits them very, very, very well. And it's not really on us to kind of prove that they don't have language. We would need to prove that they have some need for language. And all the evidence certainly is that they don't. And, you know, one of the best pieces of evidence is, that they don't build spaceships and, you know, and write books and things like that, because they would only evolve a language if they had a need to do these things.

And they don't have that need, and therefore they don't. So I think even when you look at, you know, chimpanzees and dolphins and all of these, these species that you think, well, these are the top communicators. parrots, parrots are another very interesting, another very interesting species. They, what they appear to have is a certain linguistic ability. So there's no doubt that they have a certain linguistic ability. If you think of Alex the Parrot, I don't know if you've heard of Alex the Parrot. There was African grey parrot who really did learn to speak in a way that we understand,

you know, to understand how sentences are constructed and really to understand the concepts that that he was conveying, parrots don't do that in the wild. So what we were seeing was an underlying linguistic ability. There's certain linguistic ability. There probably several species have, but they don't use it. They don't use it for language. If they did, we would see that. You know, you would see all these parrots flying around and talking to each other,

but they don't. Is it possible to pinpoint? This is probably an overly ambitious question. But even if we don't know when it happened, what happened to give human beings the capacity for language? Was it, what did we invent? Was it grammar? Was it, you know, concatenating different ideas in different ways? You know, what was that kind of transition?

Yeah, it's really hard to say. It's really hard to say, language doesn't fossilize. and you know you can look a little bit at the at the evolution of the of the vocal tract you get fossils of of that you can say oh well at this time maybe humans evolved to have more control over the sounds that they produce but the kinds of questions you're asking about grammar and about recursion and about the the structure of the language itself very very very contentious very hard to answer I think if we're going if we're going with the sort of accepted consensus at the moment that language evolved as a as a byproduct of the

complex social interactions then then probably you could say that the the the big step was could have been something like the need to communicate social information from from one to another so if you look at chimpanzees today clearly a very complex hierarchical social system with a lot of intrigue going on and a lot of alliances and a lot of shifting alliances. But you could kind of imagine if you if you have close your eyes and squint, you know, you could kind of imagine that it would be useful for one chimp to say to another, well, how about we gang up on such and such tomorrow? And that would seem to be the kind of trigger that could lead to a more complex language.

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That's a hypothesis. That's very much a hypothesis. I'm not sure how you test it. But, but yeah. No problem. And why do for a living? You just plenty of things you don't get tested, but someday we're hopeful. One of the thing I want to get on the table, though, is language is a natural thing to emphasize when moving toward technology in terms of alien civilizations. But what about just the classic role of opposable thumbs, right? I mean, is there an argument that dolphins don't have technology because they don't have ability to hold a hammer? So, as an evolutionary biologist, I would reverse that. And I would say that dolphins don't need to use a hammer. that's why they don't have opposable farms.

So there are many ways to manipulate the environment. I don't think any of us would be particularly surprised if we discovered technological octopus-like aliens. There's no reason to think it has to be through opposable funds. I mean, I know that goes against what I was saying previously about levers. Levers are important. And I think that on any on any complex, on any planet with a complex ecosystem, you would still expect to find animals that use those levers to move around.

But for manipulation, yeah, you know, you could imagine something like a starfish with hundreds of little, hundreds of little stubby fingers turning a screwdriver. I don't think opposable thumbs is, I think opposable thumbs is one of those things we've picked on. Yeah. that humans in the past have picked on to show how different we are from other animals. It doesn't seem to be very fundamental, really. That's perfectly fair. But good, this is getting us directly into the question of what aliens are going to be like when we meet them and we say hi.

I mean, it seems to me that the specifics of human anatomy or human evolutionary history have been shaped by the fact that life first flourished in the ocean, but we live in the air on the ground, right? We're lucky enough to have a planet that has a lot of water surface, but also a lot of land surface. Do we expect that, I mean, the fact that we don't live underwater seems to have been important for our development as a technological civilization. Do we expect that aliens are going to live on land also, do you think? I think there's clearly advantages to living on land, right? Fire, for instance. harnessing, harnessing energy could be a bit difficult underwater.

But that doesn't, again, natural selection will tend to have enough time to find solutions. And there may well be many solutions to energy sources underwater that simply haven't, haven't been discovered on earth because the chemical and physical conditions aren't, aren't suitable. So I'm not too, I'm not too obsessed with the idea that there must be, land-based intelligent life. I mean, one of the major targets of investigation of extraterrestrial life, forget about these billions of exoplanets, the moons of Jupiter and Saturn in our own solar system, which have large underground oceans. Now, if life is flourishing in those large underground

oceans, could it evolve to be technological, possibly? I can't immediately think what that would look like. want to speculate what it would look like, but it certainly doesn't sound impossible. I mean, it does raise a huge question about what people like creatures like yourself would do. How would you be an astronomer in an underground ocean? But presumably someone will come along and speculate, well, where are we? You know, what's the other side of this great ice that's above us? and one could imagine that such technology and such culture could arise. One thing that though, because you ask about our specific anatomy, one point that I really want to make that's really important is you can think about,

you know, if you think about the pioneer plaques and these ideas of an engraving of two humans waving and like, oh, is this going to mean anything really to an alien who receives this? and they're going to look at it. Are they going to notice immediately that that's what we are? I think there's a pretty good chance of that, actually, because one of the characteristics of our biology is that we're bilaterally symmetrical. We've got a left side and the right side. And actually, almost all animal life on Earth is bilaterally symmetrical. A few that aren't corals and jellyfish and things like that. But basically the advantages of bilateral symmetry in terms of moving.

I mean, it's just so much more effective, so much more efficient to move when you have a left side and the right side. You also have a front in the back means that we bilaterians, as we're called, have absolutely swept the planet, taken over. And that happened in the ocean. It did not happen on that. So there's another feature, another seemingly peculiar feature of our biology that would appear to be very, very advantageous and probably why. So the aliens will look at this engraving of a human and will say, well, that's a picture of something that's got a left side and the right side. That could be an organism. I totally see that happening. We do have a lot of machines that also have left sides and right sides. Right. But this is now we're sort of drifting into a new question of what about technologically created life? And many people have speculated. that when we find life in the universe, it's going to be technological.

And, you know, there are arguments in favor of that. For one thing, life has limited, has a limited existence. You know, species go extinct eventually. And you could imagine that over enough time, a civilization that becomes technological will create artificial, intelligent robots and so on. And they will persist. They will persist much longer than biological organisms could. So this is an argument that people have made.

And I find it slightly unconvincing argument, actually. But, yeah, we have machines that are bilaterally symmetrical like cars, but they're not really, they couldn't be confused for life. Perhaps in another couple hundred years, we'll have life-like machines. Perhaps other civilizations have already developed them, but we don't appear to have them yet. Let me go back to the underwater life question just to finish up one thought because it really highlights this difficulty we have, that we only have our example of life here on

Earth, right? Because you raise a very, very good problem for underwater life that you can't make fire, right? Tool use is kind of primitive. There's some tool use, I guess, among underwater organisms, but not that much. So I guess how safe are we in extra. replicating facts like that. I mean, you, I think, correctly, cautiously say, well, maybe they could figure it out, but I can't guess how they could figure it out. And is it possible that we stumble across the universe full of oceans with complex life inside and none of them have built a computer? Yeah, and that really is, that really is starting to go so far along the lines of speculation that it's hard to, it's hard to know really whether we can say much in,

that's concrete. But I will illustrate one point, which is that this is one of my favorite earth organisms. I mean, I say favorite earth organisms. One of my favorite illustrations using earth organisms. When you think about electric fishes, so there are these what are called weekly electric fishes, not many, a few species, that use electric features. that use electric fields to communicate.

Now, almost no creatures on earth use electric fields to communicate. Quite a few use electric fields to sense the world. Even some mammals do that. But to communicate, they don't. And there's a number of reasons for that. One is just that it uses so much energy. It takes so, so, so much energy. So you have to have loads of energy.

at your disposal or no alternative. In the case of these these fish, they have no alternative, no other way of communicating. But it also depends on the medium, right? So you need a medium that will transmit these electric waves in such a way that they can be picked up. And, you know, that's an advantage of being in water and not being online. So we're really quick to say, well, there's loads of things you can't do in water that you can. do on land, but then here's someone who's communicating in water in a way that you can't do on land, and we hadn't really thought of that. And there may be a lot of other examples like that, a lot of other technologies that just could be more possible in water than on land.

Fair enough. That's a very, very good point. I will think about that. But okay, with that as a caveat in mind, let's stick to animals that are on land. Animal life, Is it fair to say that when we are talking about alien life, the category of animals make sense? Is the division into animals and plants and proteins or whatever? Are these likely to be part of alien biology? Well, it makes sense to me. And I'm striking out against convention by saying that, that these aliens will be animals. And the reason is, once upon a time, I mean, when I was growing up, you know, you recognize animals by

their features, the movement and all kinds of characteristics of the animals. Okay, an animal has these characteristics. We don't do that anymore. These days, all biological classification is done by their phylogenetic tree, by their evolutionary relationships. Animals are defined very simply as all the descendants of the ancestor of the modern animals, which was a little unicellular creature that lived in the oceans, whatever, 900 million years ago, very closely related to the ancestor of the fungi.

But an animal is simply a descendant of that creature. So that then becomes a pointless definition when you talk about alien life, because by definition, no alien could be an animal. Well, if you've excluded them by definition, then that's not very helpful. So I would then go back. I'm keen on going back to the old definition, or at least part of the old definition. and saying, what is an animal actually? Well, in the context of looking at alien life, an animal is an organism.

Firstly, it's a heterotrophes. So it's an organism that has to go out and get food. It doesn't make its own food. It has to go and get it. And it's that going and getting that makes an animal an animal. So, you know, I think we could say if we were to come across a planet with lots of moving organisms, Why are they moving? Probably to find energy.

I mean, this is what life has to do. And that's really the characteristic of animals. Yeah. So no root systems, no photosynthesis. You have to go out and forage. No, I'm not not excluding the fact that you could get a root-like creature, right? That both photosynthesizes and moves. There's no reason for that.

We know symbiotic, symbiotic organisms that, that, that, you know. use, they make use of other organisms to do photosynthesis, but there's no real reason why photosynthesis should be excluded from that. But that idea of, no, I've got to move. I've got to move to get my food really is what launched the animals on the path of the diversity we see today. Yeah, and you already mentioned predation as a big part of that. So the picture I'm getting is, you know, once animals develop the ability, once life develops the ability to walk around and eat things, we're launched on a path to greater complexity and eventual technological mastery. So it wouldn't be surprising, again, who knows, but it wouldn't be surprising if

intelligent alien life was something we would recognize as animal-like. Yes, I would agree. I would agree because, and again, science fiction writers have taken issue with this, but I'm going to stick with it. animals have to solve time critical problems, whereas plants don't. So I know there are different timescales, and you could argue, well, okay, plants solve problems over a longer time scale, but they're still competing with animals. Animals are living in the same ecosystem, and animals are working at a much shorter time scale.

So, you know, when a plant solves a problem that it faces with an animal, it's different from the way an animal solves a problem with an animal. You've got to make decisions quickly. Things are changing all the time. Everything's moving around you. Your food's moving away from you. Someone's coming to eat you. And that really appears to have been a strong driver of the evolution of intelligence.

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because it feels like this, right there. That's farmhouse, fresh skin. all right. I'm blowing and everyone asks how. The best skincare is farmhouse fresh and the award is you, your best you. Visit farmhouse fresh skincare.com and use code radio for a free starter routine with any purchase. Good. So far, all right. I'm with you here. So we go to the other planet, we go to Alpha Centauri and there's some planet around there that has animals on it. And now we're starting and get specific. So the animals live on land, and you've already made a pitch for bilateral symmetry. What about arms and legs and heads? I mean, are these basic recognizable features likely to also be part of alien biology? Well, like I said, if you're moving on a solid surface, then then

limbs seem to be so efficient that, that, you know, it's just going to, it's going to be, they're going to be the dominant life form. If everyone's running around, trying to eat each other, If you've got legs, you can lift yourself off the ground, then you've got a huge advantage. Now, of course, there are many animals on Earth that have lost their legs, things like snakes, right? They're exploiting a very specific niche where legs would just get in the way. But that's a specific niche. The idea of limbs, I think, has been hugely, hugely successful. And, you know, you can see from the development of the arthropods of the insects, that the huge diversity of insects,

is largely down to the fact that they have the so many options for what different kinds of jointed appendages they can have legs, you can have wings, you can have antennae, and that's really allowed them to exploit such a wide range of niches. And this is what happens. When there's a lot of potential variation in the morphology of an organism, then you tend to get, our diversity of niches, a diversity of ways of exploiting the environment and exploiting other organisms. It's a good point because as you say, not every land-based creature has legs, but most of them do it. And there's sort of some good reason. And this is part of your sales pitch, right? That there are physics-based reasons for the specific solutions that life has found to these

puzzles. Well, there are some physics-based reasons. Yeah. Some of the constraints are definitely in the realm of physics. Some of them are not. Many of the constraints are more based on the evolutionary interactions between organisms. But yeah, a good starting point is the physics, for sure. And okay, now just in the middle of this conversation is the first time ever thinking about this, but even though so many organisms have legs, remarkably few have arms and hands in some sense, right? arguably some other primates. I mean, definitely some other primates,

kangaroos, but most of the life forms that come immediately to my brain use all of their legs in a sort of similar way. Is that something we should be surprised about or does that make sense? I'm not entirely sure that it's even true. I know that I certainly,

if you think about mammals, it's largely true, but as you say, the primates are rodents, use their paws to manipulate things. If you ever seen a squirrel, eating a nut, you know, it's quite common. Birds have a bit of a problem because they need two of their limbs to fly with. So that doesn't leave them very much flexibility in that respect. And yeah, I guess amphibians and other, some reptiles do.

But I think it's probably going a bit far to say that most animals don't use their legs. Intects, insects certainly do crabs, I mean, crustaceans. That's a very a counter example. I guess I'm just thinking of, you're right, there's a continuum, I guess. In human beings, the roles of arms and legs have just completely differentiated in a way that in a raccoon or a squirrel, they still walk on all fours, right? How bold can we be when thinking about the aliens to say, technologically advanced aliens are likely to walk on two legs or will they be like centaur

like having four legs and two arms what are the constraints there from biology or physics or whatever well they have an even number i think i think if they're bilaterally symmetrical they have an even number and i think that's that's a good thing that's place to start the the transition to bipedalism among humans is another controversial issue just about everything in human evolution is controversial. There are all kinds of ideas about why humans developed the ability to walk on two legs. And a lot of those ideas, a lot of those hypotheses have got to do with manipulation, so to leave your hands free to manipulate. But there are plenty of other ones, you know, so you can see above the grass, so you don't get as hot in the sun. Loads and loads of explanations. Enough explanation, enough

explanation, enough plausible explanations to make you think, well, this doesn't seem to have been a fundamental transition. Okay. This really doesn't. This seems to have been something that, yes, was crucial on the path to our evolution because of the specific situation that our ancestors were in in a forest world that was that was rapidly being converted into grassland, for instance. And, you know, this was just the way we needed to be. We needed to run faster to carry things. you should carry food from one place to another because it wasn't just any old tree that would have fruit in it. So that was very specific to our evolution. And I don't think anyone has any difficulty looking at a raccoon, for instance,

and saying, well, I can imagine a raccoon flying a spaceship. And, you know, we can, right? No, it's a perfect example. I've seen it. I've seen it on TV. Okay, very good. So I wonder, I want to switch over to the sort of social linguistic aspect. of these wonderful thought experiments we're doing. But just to put a cap on it,

you know, to what extent are there laws of biology? I mean, I know there's sort of scaling laws that we see in different species here on Earth. We have networks inside of us that seem like a naturally efficient kind of system, that maybe that would also be the case in aliens. So are there laws? Are there right size?

Do we expect intelligent aliens to be meters high rather than hundreds of meters high or millimeters high? I mean, what can we say about the possibility space there? There are laws, and the laws tend to be, well, the laws that we understand really well are the laws of natural selection. We haven't spoken much about natural selection, and even my main premise, which is that natural selection is what will be driving complexity on other worlds, which some people can

test. But we understand the laws of natural selection pretty well. We've got pretty good models of how natural selection works and how kinship plays a role in natural selection and an important role. But, you know, when we do speculative biology and astrobiology and so on, we are constrained by our understanding of earth biochemistry. So a lot of the questions that you asked about size and networks and so on are to do with the biochemistry that we understand on Earth. And although, as I said, water is very common in the universe, and amino acids are dead easy to make, and they're probably everywhere, and so it's very likely that alien life will be based on a carbon chemistry

somewhat similar to ours. We don't know that for sure. And you can just think about some of the recent talk about life in the clouds of Venus, for instance, you know, really chemical. extreme environments and what kinds of chemistries might exist there. So I think it's hard to be sure that the kinds of constraints that exist because of chemical and structural constraints on Earth would be the same ones on other planets. But on the other hand, I wouldn't be surprised either, precisely because these chemicals are so common and so reactive. So I don't know. I don't think

I don't think I would like to speculate on size quite as much as that. But yeah, within a couple order of magnitude, either way, probably a reasonable window. I guess I should have asked earlier more about the biochemistry. I mean, obviously life on Earth, as we know it, is very, very dependent on this relationship between DNA, RNA proteins, right, in a very, very specific way. And there's kind of basic chemical reasons why. I mean, can we be so bold as to imagine that that would be a feature of alien life as well? I mean, DNA is just such a good molecule for sending information down through generations.

There's really no competitor to it, or might there be that we just haven't thought of yet? Well, there's no competitor to it. That there is no competitor to it is no real surprise. We don't know whether DNA was the only, or RNA was the only form of life that evolved on earth. There may well have been competing biochemistries that have all gone extinct, which you would expect if DNA were a much more efficient way to run things. So we don't know that. People are trying to work on these ideas.

But what we do know is that it's not DNA that's special. okay that is not what's special about life what's special about life is the ability to inherit traits and and variation and with with for one generation to pass its traits on to to the next generation that is what's essential for natural selection um must have been done through DNA that one could speculate and imagine all kinds of other ways I can't because I'm not a biochemist And I dare say that many of those ideas and many of those alternatives have really strong arguments against them in terms of stability and energetic efficiency and so on. But I wouldn't get too caught. I don't get caught up on the whole DNA thing because, yeah, there's certainly there's got to be other ways of doing it. But some form of heritable information is essential.

You know, that's certainly my inclination, but then I have friends who are building microscopic robots and computers at the molecular level, and they're doing it out of DNA. And I said, you know, why? Because there's a lot of DNA around. And they say, no, it's because it's just the right molecule to do this. It contains information and it lasts a long time. So I don't know, maybe some version of DNA, even if it's not exactly like we had here on Earth, might be common to alien environments. Yeah. And of course, although they don't actually use, they're not using DNA because it's here and it's available.

They're using it because it's inspired them. And if they had seen another molecule that did something similar, they would be using that molecule. Yeah, absolutely fair. You did say one kind of provocative thing that I don't want to let completely escape. The relationship between evolution, natural selection, and complexity, you know, famously evolution is not teleological. It's not oriented toward making things more complex, but it has happened that the very complex organisms have arisen through natural selection. So you think that that's a natural thing to have happened, and you seem to be implying that

not everyone agrees. No, I think that's, I think people agree with the idea that that natural selection will tend to increase complexity. I think that's, that's uncontroversial. I think I've had people say to me, for instance, how do you know that natural selection is the force driving life on other planets? How can you be sure? We only have one example. And that's a relatively easier argument to dismiss. Largely, probably the best argument in favor of natural selection is it just happens so easily. You know, you really don't need very much for natural selection to get going. You need to have this variation. that's heritable and you need to have some sort of differential fitness, some configurations that are more efficient than others, and it just goes. It just goes all by itself. So apart from the fact we can't think of any other mechanism, which is perhaps a weak argument, there's the argument that natural selection is just so easy to set off.

So it's going to be out there. Sure. Yeah, that I'm completely willing to sign up for. So good, let's move into the completely crazy speculative parts of this question. We have our bilaterally symmetric aliens who might have legs and arms and things like that. How do they talk to each other? How do they communicate? Is it going to be like the Borg?

Are they going to be a collective intelligence? Do we have reasons to believe that individuality is a crucial part of advanced technological civilizations? Or is that just a little anthropocentric? Well, communication, of course, it's there everywhere. All animals communicate. Plants communicate. And it's important, first of all, the first sort of ground rule to lay down is that communication always evolves from sensing. All communication has evolved from sensing, sight, hearing, everything, everything.

We hear because, you know, we speak in words because we can hear it. It's not the other way around. We didn't evolve ears to speak. And that's really key because that's one of the reasons why there's no telepathy. Even if you could think of a physical explanation of how telepathy could work, it wouldn't evolve. It would never evolve because there's no point in sensing brainwaves if no one's transmitting any brainwaves. And there's no point in transmitting your brainwaves if no one's evolved the means to listen to them. We evolved vision because we could use light to find food, irrespective of anyone communicating.

We didn't involve vision to see other people, other people were waving at us. We didn't involve hearing to hear other people speaking. We evolved hearing because it helped us to detect movement in the water around us. So communication evolves out of sensory systems. What sensory systems work well depends on the physical environment. So already mentioned electric field sensing is really rare on Earth, but there are conditions in which it could be fantastically effective. I mean, it's really, it's a good way to communicate.

You can put lots of information into it, and it travels long distances with very little loss. It's a great way to communicate. It's just really expensive. Now, light vision, is of course really common and sensing by by sight is one is very very old very ancient ability and plenty of unicellular organisms have have that ability as well so so vision is is a is a good communication medium if you live in a transparent medium and you know even

if you live in transparent medium again coming back to Enceladus and Europa and things you live in an underground ocean, well, there's no light. So are you really going to generate light? Why would you bother generating light if no one can see anything? It's hard to see how light could evolve under those circumstances. I mean, you can imagine cases. Underwater volcanoes might produce some light or something like that. But basically, you need a transparent medium. The other interesting thing about light is, and again, we're talking about the scales that we believe in now sort of size and a couple more than magnitude bigger and smaller. Because of the wavelength of light, it's kind of useless when something's in the way.

It doesn't really go around things at all. And so you could be hiding behind a bush and no one can see you, which in itself drives a lot of, of course, drives a lot of evolution, a lot of diversity and different ways of hiding and different ways of finding other animals that are hiding. But sound does do that. sound has a wavelength that's long enough to travel around objects and it travels long distances and it carries a lot of information and the fact that we use sound to speak right now is no coincidence it's just a really really really good way of communicating in the kind of environment in which we live of course if you go to mars it's got a very thin atmosphere you're a bit stuck The sound is not a great way to communicate there.

But these kinds of ideas, these physical constraints on what communication modality communication channel will work, that's definitely another physical constraint that's going to apply equally on any planet. I mean, sound going around corners, clearly very useful. I agree with that. But we can imagine very different environments. Like you said, thin atmospheres,

or on the other hand, what if it was just a very noisy, environment, so it's hard to rise above the noise. I'm kind of intrigued now by the idea of using light in the way that you and I use sound. So not only to see things, but to generate it, like glowing and sending signals that way. I mean, that'll be an intriguing way for aliens to talk to each other by beaming signals at each other. Yes, except the other, the other problem with the wavelength of light, is that it is actually very hard to detect it. So when you think about how we detect sound, we have a frequency analyzer in our ears. So we have a series of

hairs of different thicknesses and lengths, and they respond differently to different wavelengths of sound. And that's why we can hear sound in great, great, great detail. Although we tend to think of our vision as being very acute, it's very acute spatially. So we can tell the, we can distinguish two points that are close together very well because we have lots and lots of light detecting cells in our eyes, but we're really bad at detecting frequencies. I mean, all we can do is put colors, you know, color filters in and look at the red, green, and blue. We don't have a system, and it's hard to imagine a system that would detect light by its frequency in the same way that we detect sound by its frequency. So we think that aliens are going to talk.

I think that I think that that sounds are really I think that sound is going to be a really common way of communicating. I've got to say one thing, right? Everything that I say, it's quite likely that we'll find a counter example somewhere in the universe, right? Weird things are going to happen, but they're going to be really rare. They're going to be rare. The obvious solutions are going to be really common. And yeah, sure, we'll, we may find. something that, I don't know, hasn't evolved through natural selection. Well, maybe not that,

but some strange stuff is going to be out there. But almost all the stuff that we find is going to be very straightforward. You know, if you're living in a dense gas atmosphere, you'll use sound to communicate. Yep, absolutely. In a sense, because of the combination of the fact we all live in the same physical world, plus the fact that natural selection looks for good solutions, you know, we will find good solutions over and over again. Yeah, natural selection finds good solutions. It doesn't look for it. But okay, I think we skipped over the individuality versus collective question. I mean, this seems to be a big question to me.

We're very, very used to life taking the form of individual organisms. Is that a blinkered parochial point of view that we have, or is that another one that we should expect to be very common? Well, here's a good example of looking at human evolution, and we have to be cautious, right? We have to ask ourselves, are we being two anthroposcent? like with the bipedality, are we going to, are we really sure that's what's important? But on the other hand, as I said, our ancestors, social primates, complex social societies, probably.

And what appears to have driven the evolution of language and the evolution of intelligence as we understand it seems to have been conflict. Right. So the potential for conflict. So I've got to decide, am I going to cooperate with this, this member of my group, or am I going to fight with them? and who am I going to cooperate with to achieve my aim? So that kind of conflict drives intelligence, just in the same way as problem solving drives intelligence, or other animals that an octopus that needs to open a jar to get some food or something like that is problem solving. You don't need intelligence if you don't have a problem to solve.

So if we go with the idea that human intelligence, human language evolved because of conflicts in pre-human society, then that would tend to argue against a society without individuals or society of clones like bees or termites or something like that, leading to that kind of intelligence. Yeah. Okay. Yeah. Interesting.

I mean, the conflict, I kind of translate that in my brain is just saying that life is harsh, right? Like when conditions are tough, evolution needs to work harder to find clever solutions. to things? Is that an oversimplification or is that basically the right idea? I think if things are harsh, then it's more likely that complex solutions will provide an answer. So complex solutions are likely to arise because they will provide a better way of dealing with things. So you could imagine, you certainly could imagine a colony of bees and they can really only survive in their environment if they cooperate more, if they exchange more information between them. And so they have to know exactly how to open the flowers or something like that. And so they have

to convey this information to each other. And so a kind of language develops. One could hypothesize about a situation like that. However, you know, clones cooperating is a little bit different from individuals cooperating. And the best example that we have is multicellularity itself, right? We are a collection, each of us is a collection of clones, of cloned cells, cooperating extremely well, communicating a great deal of information. We think about all the information that goes around our bodies, not talking about our brains, just our immune system and so on.

So that's an example of clones cooperating together to achieve. a complex goal. Is it the kind of intelligence that we're looking for? Hmm. Seems to be a bit different somehow, doesn't it? It does. But it's not going to stop me from asking enough for bold question, which is families, sexual reproduction, you know, like how, again, it's obviously a huge worry that we're

only seeing things through human colored glasses here. But sexual reproduction does seem to be a real. really good solution to various evolutionary problems. You can imagine how sexual reproduction leads to kind of pair bonding situations. You know, are we crazy to think that alien societies might have not the same, but related kind of social structures for those reasons? Well, for one thing, reproduction is essential for natural selection. So reproduction of some sort there's got to be.

And what's interesting, if you take a sort of very broad view of kinship, then you don't need sexual reproduction to have kinship. So if I'm an E. coli that's just reproducing asexually, producing clones with occasional mutation, it's still the case that I will be more closely related to my immediate descendants than to my distant descendants. So there's still still. kinship, even though there's not sexual reproduction or partners or societies or anything. And that kinship still will play into very important part of evolutionary theory, which is kin selection. So you're more likely to cooperate and to sacrifice your own good for those organisms that share much of your genome. So we can see kin selection happening even without sexual reproduction.

We could in theory see whole societies, whole families based on kin selection without sexual reproduction. But it seems unlikely. It seems unlikely because what we know about life on Earth, we look at the diversity of asexually reproducing organisms on Earth. And some people who will say that the diversity of asexually reproducing organisms is huge because there are, There's billions of different species and subspecies and kinds of genomes, but, you know, they're all bugs, right? And they're all little bacteria or something like that. The phenotypic diversity is very, very, very small. The diversity in form and the diversity in niche is actually quite small compared to multicellular organisms.

So there's something going on. There's something going on in the way that sexual reproduction, which is very ancient on earth, we believe. The way that sexual reproduction is playing into the niche diversity, the diversity of roles that different organisms have and mostly for multicellular organisms. Sexual reproduction on earth is down to DNA. It's down to DNA. Got two parents.

What can you do? Does it need to be that way? No, if life is not based on DNA, which you know, you might think it must be, but if it isn't wild, or even actually, even if it is based on DNA, there are ways of having multiple parentage, multiple inheritance. So some kind of sexual reproduction appears to have helped to drive the diversity of life on Earth. And like you said, there are evolutionary problems that it overcomes, problems about how you get rid of, of disadvantageous genes and things like that. And there are all kinds of reasons why we might expect sexual reproduction to arise. It doesn't seem to be, it doesn't seem to be unduly Earth-centric to think that

some form of sexual reproduction will arise on another planet. Or at least, let me put it this way. If we see a complex ecosystem on another planet, chances are there will be sexual reproduction. You can't predict that it will arise on any particular planet. But with hindsight, if you see a complex ecosystem, it's hard to see how that could arise purely from asexually reproducing organisms. All righty. I mean, we have to wind up.

I know that you have a cutoff. So with all of these considerations on the table, I guess one thing we haven't mentioned out loud is the fact that if we do meet alien civilizations, they're likely to be at an extremely different stage of development than we are. And there's an ongoing debate about whether or not we should even want to meet them. Do you put ourselves out there or is it too dangerous? You know, like how crazily far can we extend these considerations to wonder about the friendliness or sociability of aliens where we do ever meet them?

Well, I'm not concerned myself. And that's for a number of reasons. One is that, of course, you can argue all you like about whether or not to send messages to aliens, but we've been doing it for 100 years without meaning to. So any alien civilization that has anything like the technology necessary to come and visit us already knows that we're here. There's no hiding. Absolutely not. We've been looking for alien civilizations with our primitive technology and haven't found any, but you could imagine that anyone who's out there who knows what they're doing would be able to find us. So I think the cat's out of the back.

But on top of that, you know, the chances of actually having some kind of technological solution for traveling between stars is pretty slight. We don't know. There may be solutions. There may be technologies that can do this. But if there are technologies that will allow an alien civilization to travel from one star system to another, They are so technologically advanced and they have so much energy at their disposal. Why would they bother harming us? You know, our preconceptions and our fears of alien civilizations are entirely based on human behavior and entirely based on human colonialism where we needed to go to another country to take all the gold or, you know, to take all of the slaves because we didn't have enough.

stuff here. But if you can travel from one star to another, you can make as much stuff as you want. You can make as much food as you want. And really, planet Earth isn't giving you anything. There's no, the colonialism in an interstellar sense doesn't even seem to be logical. I don't see what people would be wanting from other planets. If you can get there, you can make what you like. And then the third argument, of course, a slightly more depressing argument, is that it's not at all clear that most technological civilizations will survive to that point. It's not clear that we will survive the next couple hundred years. Technology seems to be highly, highly damaging to a civilization.

So you can imagine that anyone that has reached that point, that has managed to get over all of the kind of disastrous social plagues that we have here, climate change and wars and racism and any civilization that can get past that and survive to the point of becoming technologically advanced, they're probably pretty nice, guys. I like that optimistic spin. I'm not sure that I'm happy to take it for the moment. I mean, so, okay, last question then, you know, if you had to bet, right, I know there's no way of judging these things in the short term, but do you think that there's a federation of of planets out there that will someday hook up with, or do you think that it'll be mostly

worlds full of slime and will be the alpha dogs? Yeah, I tend to think there isn't. I tend to think that if there were, it would have been more obvious than it is, but I certainly don't discount. We haven't really looked very hard, to be honest. Our seti work has been pretty focused and pretty minimal, we've covered a very tiny, tiny range of the possibilities. So I'm not sure. I tend to think there isn't, which is disappointing because the biggest disappointment to me as a zoologist is that I'm never going to see any of these alien animals, right? We're never going to travel to any of these planets, never going to be able to watch them. The only hope, the only hope that I have is that somewhere out there, there's an alien David Attenborough who's going to be sent.

ending us TV shows showing all of the animals on their planet. And that's the only way we're going to find out. As long as we can figure out how to build a DB player that works with alien technology, that'll be the tricky part. But I like the possibility of getting the shows from the BBC, Alien BBC. So Ari Kirkland, Ben, thanks so much for being on the Mindscape podcast. Thank you so much. Okay, so for the final trivia question,

What is the largest mammal in the world? Reminder, no phones allowed. Sir in the orange, phone away, please? Um, my kidda smart smoke alarm sent an alert through the ring app. Okay, sure. No, there's smoke in my house. Yeah, right. A smoke alarm texting you. That's a new one.

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