The Tree of Life: Mapping Evolution’s Greatest Story, with Max Telford
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Welcome to Intelligence Squared, where great minds meet. I'm producer Mia Sorrenti. Understanding how the diversity of life on Earth came to be is one of the greatest puzzles in biology. In his new book, The Tree of Life, Professor Max Telford charts a four billion year journey through the evolution of our planet, from humans, fish and butterflies, to oak trees, mushrooms and bacteria.

On today's episode, Professor Telford sheds light on an epic history of the family tree that records the relationships between every living thing, from Darwin's early sketches to the vast computer-generated diagrams scientists are building today. Professor Max Telford is an evolutionary biologist and the Jodrell Chair of Zoology and Comparative Anatomy at University College London, where he founded the Centre for Life's Origins and Evolution and the Telford Lab.

Joining Telford to discuss the book is Ganesh Taylor, fellow at the Centre for Reproductive Health and Science Communicator. Let's join Ganesh now with more. Welcome to Intelligence Squared. I'm Ganesh Taylor. Our guest today is Max Telford. Max is an evolutionary biologist and the Jodrell Traer of Zoology and Comparative Anatomy at University College London, where he founded the Centre of Life's Origins and Evolution and of course the eponymous Telford Lab.

He has spent the last three decades researching the shape of the tree of life, his broader aim to discover the earliest events in the evolution of the animal kingdom.

Today we'll be discussing his latest book, The Tree of Life, as you can see here, Solving Science's Greatest Puzzle, a four billion year journey through the evolution of our planet, charting the fascinating story of the gigantic family tree that records the relationships between every living thing, from humans, fish and butterflies to oak trees, mushrooms and even bacteria.

Welcome to Intelligence Squared, Max. Thank you very much. Great to be here. It's our pleasure. I guess the first question I would have to ask you, realistically speaking, is what actually is an evolutionary tree? It's one of those things that sounds familiar to most people, I'm sure. Like we get a sense of it, but there's a technicality to it, right? Like how are they built? What actually is it?

Well, I guess it all started with Charles Darwin, who realised that rather than species being created by God in an instant, species had come to exist over time, over vast periods of time, in fact.

And the best explanation, the one that Darwin came up with in the 19th century, was that there was an initial event which caused life to come into existence, which is an extraordinary tale in itself. But since that moment, that single first species has gone on to divide into more species.

And that over time, those species have become different from each other. And that's how we've got to what we can see outside our windows today. So there's not a lot I can see outside my window here in London. But if you go into even in our garden in London, we see foxes and trees and bluebells and butterflies, etc, etc. And so all this extraordinary diversity of life that happens.

we can see around us has appeared through evolution. There's a process that started off with a single species and that over many, many millions and billions of years has produced the species alive today. And that process by which the species were produced, were made and became different from each other can be described by a tree of relationships.

So I have to ask a bit of a naive question here. So I was thinking, you know, why do human beings do this? I mean, you said Charles Darwin started this. I think Linnaeus is another character that you mentioned and some of our audience will have heard of as well.

Is there like a bit of a compulsion for human beings to categorise stuff or to try and figure out their relationships? And are these evolutionary trees kind of just like really complicated versions of basic family trees that I'm assuming humans have always been interested in? Well, there's kind of two parts to your question there, because one of them is categorisation, where we're always keen and the Greek philosophers were keen in working out

what ideals were, what things could be lumped together as more or less similar. So Aristotle was very interested in working out characteristics which lumped groups of animals together. But he had no idea of evolution, so as far as he was concerned, he was looking at ideals or whatever.

Linnaeus, similarly, his classification was a practical one. It was a way of finding the characters which allowed you, if you considered them one by one, to put a species that you had in front of you into bigger and initially big and then smaller and smaller and more precise groups.

so that if you were a botanist, you were trying to cure somebody's headache with a plant, you could make sure you were looking at the right plant and you weren't going to poison them. So categorisation is something that we did without any knowledge of evolution or that these species that we're looking at were actually related to each other. And the family trees, on the other hand, is something that we sort of realised that the species could be put into family trees much later. So we were obviously all interested...

in our own family trees over probably only a couple of generations and over their family trees of kings and caesars and czars over hundreds of years. So I think those two things come together and meet when we realise that animals are related by this process of evolution.

So, you know, you're saying on one hand, humans have always enjoyed categorization as an activity of other animals and organisms and, you know, putting things of a different kind together. And then, of course, separately, we're kind of interested in our own family, family lineages and, you know, especially royalty. You know, we know about that historically being very important. And what I'm hearing, at least, and what I picked up a good amount in the book is that there's a sort of moment where, you know,

you know, the evolution of species via Charles Darwin's work, et cetera, pulls together this situation where suddenly these two things are kind of related to each other, right? Suddenly our family trees go way back further beyond the edge of the tapestry into a realm where suddenly we're connected to all of these different animals. But of course, before we're categorizing by kinds, like as in by what we see them as looking like. So the question here is,

Have there been any upsets? I'm guessing there have been some upsets in terms of categorization of organisms that look like they may be related to one thing. And then once you check their DNA, presumably, is that what's being used?

it turns out that they're more or less related to others? Yes, so Linnaeus and Aristotle were looking at the outside appearance of organisms to make their categories. And very often those categories that they made actually conform to the branches of the tree that we now know are true. So Aristotle had a group called essentially the blooded animals, the animals with blood, and that corresponds to the vertebrates.

and he had things that laid eggs and that were the reptiles and the birds. So these groups you can do using, you can find these groups, these classifications turn out to map onto the tree of life we have. And then of course we make mistakes when we're just looking at morphology. We make mistakes even when we're using the vast amounts of information that we have in DNA. And a good example, there's a

I work on invertebrates, so I'm particularly interested in the sort of weird, wormy things that live in the sea. But there's a group called the sea squirts, which are very common animals. They're rather ugly, live attached to the bottom of boats, for example. And these were classified for a very long time as mollusks because they sort of look like mollusks. They're squidgy and rather plain and they don't go anywhere. They just sort of sit there filter feeding.

And so this turns out to be a mistake, that we were confused by their outward appearance. And at some point in the 19th century, it was discovered that the sea squirts actually have a stage in their life, they go through a larval stage, and the larva looks exactly like a frog's tadpole. And it turns out that sea squirts are not related to mollusks at all.

But the clue is in their larval stage, which looks a bit like a fish or a tadpole. It's got a mouth at one end and a tail, etc. And so that's a very easy example of one of the mistakes we've made.

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you know, the classifications that were made well before anyone knew about DNA or evolution hold so true. And it reminds me of something else that I wanted to ask you about. So you were saying that at some point scientists presumably were looking at the development of this organism, the C-square, and then they realised it went through a different sort of stage of life where it looked a bit like a different organism.

And it reminded me of something called the phenotypic stage or the phylotypic stage of, well, it's referred to often in human development. Of course, you know about that. I think it would be really interesting to our audience to be told both about that and whether or not that that sort of fed into our understanding or thinking about evolutionary trees or the first trees that were being drawn. I kind of think it's the other way around. So there's this, within the animal kingdom...

some of the oldest most distantly related branches are these branches which we call phyla so these are things that are very have very different body uh body plans and we can't really work out how that these are the most difficult problems in terms of working out how they're related a phylum would be the arthropods which are things with a

jointed legs like crustaceans and insects, the molluscs, which all have a shell and a sort of squidgy body, and the chordates, which are things like us, which have a backbone. So those are three phyla. And they separated from each other a very long time ago in a period called the Cambrian, about sort of 500, 540 million years ago.

And the phylotypic stage is a period during their embryonic development. They all start off as an egg, so very, very simple. And at some point, all the members of a phylum

come to resemble one another, and that's the phylotypic stage. So however different their eggs start off looking, so they might have big eggs with lots of yolk or little eggs with very little yolk, all the chordates pass through a stage when they all look very similar. So a human embryo will look like a chick embryo, will look like a fish embryo.

And we get the same period of development in the arthropods and in the mollusks. They all pass through what we call this phylotypic stage, which is sort of the stage where the sort of fundamentals of the body plan of that phylum are laid down in development.

That's pretty incredible, isn't it, when you stop to think about it. So what's the relationship between that? So people start to look at the development of organisms. Were we making evolutionary trees before that point? Or was this a complete surprise? I think people, even before Darwin, people were looking at embryos and realising that they could classify organisms, even in a pre-Darwinian sense, so a non-evolutionary sense, who just classify things that are similar to each other.

and discovering these deep relationships based on the similarities of their early embryology. So the sea squirts is one great example. Another really nice example are the barnacles. The barnacles are these things that you see encrusting rocks by the seaside. And they look rather like limpets. They sort of live side by side with limpets. And they were initially classified as mollusks. I think everything seems to get lumped together with mollusks.

But the barnacles go through a stage where they look... A larval stage, again, a developmental stage, where they look exactly like a crab. And so this was when it was first realised that barnacles are crustaceans. And they look weird because they've started...

They've stopped running around looking for food and they've settled down on a rock and they feed completely differently. They don't need to move anywhere. They can use their legs for other things. So they can use their legs to catch food in a very different way. They have these big shells, which they need to protect themselves. And so evolution has made them look very different from their phylum. But nevertheless, they go through this phylotypic stage, which shows that they are indeed arthropods.

So to really nail this down for my little simple brain here. So are evolutionary trees built on genetic information?

Evolutionary trees can be based on any character that is inherited. So ultimately, the characters will be encoded in the DNA so that they can get passed on from generation to generation. But those characters can be the DNA itself or the proteins that the DNA codes for or the phenotype that the proteins produce. So the shape of the body or the colour of scales or whatever it may be.

And for some organisms, of course, we don't have any DNA. So for fossils, we only have

their phenotype. So for huge bits of the tree of life, we can only use phenotype because most species that have ever lived are now extinct. Okay, so then I have to ask two things. I think you clarified there, so the tree of life encompasses things that are both alive and are no longer alive in that case, that's an important thing to say. But then

It sounds like there could be quite a lot of different versions of the tree of life, depending on what bit you're looking at. Is that fair to say? Well, what's fair to say is that if you've got a dozen species, there are literally millions of ways in which they could be related. So there are literally millions of trees that could relate just a handful of species. And so the number of potential trees of life

that we could decide are the truth, it's absolutely impossible to count. And so we have to try and find ways of finding the truth. So there is one tree of life, but which is it? Is it the one where C-squirts are related to mollusks or the C-squirts are chordates, etc., etc.? And there are countless questions like that which we need to sort out in order to get to the answer.

Okay. And I mean, at the risk of sounding a little facetious and how exactly do we do that? How do you do that more correctly? How are you doing that, Max?

What we're looking for is things which define branches of the tree. So, for example, we're looking for characters which are unique to a branch and not found anywhere else. So, for example, one single branch of the animal tree are the chordates. And the chordates share a number of characters. Most obviously, they have a backbone.

And so this is a character that is unique to the chordates, not found anywhere else. And so anything that has a backbone must be a chordate, and anything that doesn't have a backbone must be somewhere else. And so that one single character defines one branch of the Tree of Life.

And so then we just need to look for more characters. So we look at more and more characters and these can be bits of our morphology or our embryology, as we've discussed, or they can be bits of our DNA. So we have, we share DNA with the whole of life. So there's some genes that,

some genes that are present in everything from humans to bacteria. And if we look at those genes and look for changes to the DNA sequences of those genes, we can use those in exactly the same way as I've just described for their backbone. So there can be a change in one tiny bit of the DNA, which is then passed on to all the descendants of that creature at that time, which defines them as a group, defines them as a branch of the tree of life.

Amazing. I mean, I know we've like dived straight into there about what are evolutionary trees and all that sort of stuff.

To sort of step back out a little bit, I want to ask you to tell us a little bit more about something that you referenced in your book, which piqued my interest. You mentioned that we have a zoological equivalent of an embarrassing uncle at a family party, some sort of worm called a Xenotorbella? That's right. This is a very odd creature. And it was for a long time. I've worked on it for 20 years. And to put it mildly, not everyone agrees with me.

about where it belongs on the animal tree. Anyway, so the worm started off as a very simple worm and it was thought to be related to the flatworms, which are things that include, it's a phylum of worms that includes the things that, tapeworms and things like that, because they're very similar. They're very similarly simple, should I say.

But the first DNA that came from Xenotabella showed instead that it appeared to be related to the mollusks. The mollusks seemed to pop up the whole time. And I started working on it at this point because it seemed very, very unlikely that Xenotabella, this very simple worm, was related to the mollusks because it doesn't look anything like a mollusk.

And what we discovered was that this first experiment that had looked at Xenotabella and got DNA out of it had made a mistake. And they'd actually got all the DNA, they'd ground up a whole adult organism, and the DNA that they'd actually analysed came from the contents of its stomach. And it turns out that it eats mollusks. It eats mollusks. Wow, okay. So...

So then we went in and did some experiments to show you this and found the real DNA from this worm. And we showed that it wasn't related to the flatworms, as everyone had believed. It wasn't related to the mollusks, as seemed the mistake that I've just described. And it turns out, according to me at least, that it belongs to a group called the deuterostomes. And the deuterostomes is a great big branch of the animal kingdom that includes the chordates like us. So it turns out that this very simple worm

is actually relatively closely related to us, which was a huge surprise at the time. Wow. Well, there's a lesson in that as well, isn't there, in how experiments have to be reproducible to actually give us the information they want. I mean, so, you know, you say yourself that you've been working on this for like 20 years now, you said, right? So I guess maybe this would be a good moment to then ask you,

What was it that motivated you in that case into writing this book? I mean, this is not a, you know, you've got a PhD, you've graduated a few students, you've written a book already of your own, as it were, an academic book. What drove you to writing another book? I must say, I didn't write the previous one. I was the editor of it. So this is my first foray into actually writing a whole book.

I love my subject and I think it's incredibly interesting but probably fairly little understood. So I think people know about what

roughly what a tree of life is, and there is one. But it's very interesting, I find, in understanding how a tree of life is made and the mistakes we can make in doing so. The mistakes are almost always interesting, in fact. So I've told you some stories about how Xenotabella, because it's very simple, everyone thought it was a flatworm, but it turns out...

It's related to more complex things. And so these things that confuse us about building the tree of life are often some of the... Well, they're what challenges me every day, but they're often caused by some of the most interesting bits of evolution. So I really wanted to get across this field that I'm so passionate about and how...

I think the most important thing, the most important message of the book is that the tree of life is, if we know it, once we know it, it's something that can take us back in time. And it's this sort of foundation, should I say, of understanding our own history. And if we don't know how we're related to everything else, then we can't know our own very long, long history. Yeah, that's a really interesting way of putting it. And within that, obviously, you're also acknowledging the fact that

people tend to have a bit of a people-centric view on life. They're very self-orientated, generally speaking. You know, we want to know about ourselves. And one of the fun examples that got mentioned in the book that I'd love for you to share with our audience today is about the human chin.

which apparently doesn't exist, or does it exist? The human chin does exist, but we're the only species that does have a chin. So none of the other apes have a chin. If you think about a chimpanzee, it's sort of, I've got quite a big chin, but we all have chins. I'm feeling quite self-conscious right now, yes. But the chimpanzees don't, for example. They're our closest ape relative. And the point really that I was making there is what,

We often want to know why things have evolved. And we can tell stories about that. So I could come up with theories about how my chin evolved. But if we've only got one instance of the evolution of a chin, then it's much more difficult to come up with a scientific way of testing it. This episode is brought to you by Peloton.

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So just to be a pedant here, because, you know, we were saying before about characteristics and how we classify things. You know, my cats have what I would normally have called a chin, but yet you're saying it's not a chin. So what is a chin? You've really got me now because I'm not an expert on words. But the chin is the fact that it sticks out in front of our lower teeth rather than the...

All jawed vertebrates have a lower jaw. So it's not the lower jaw itself. It's the protrusion beyond our teeth that makes it a chin rather than just a lower jaw.

So fun, so fun to hear about. There's actually some pretty cool papers out there looking at this stuff. But that leads us also on to talking about something that I personally think is really interesting to tie together a bit of what we've touched on before about embryology, so early embryonic development and our similarity to different organisms and the chin thing that we just mentioned. So

The chin is part or as an outer structure, let's say, of the jaw. And you've already alluded to the fact that there are many jawed organisms. And the appearance of the jaw on the tree of life is kind of an important moment, is it not? I'm loading this question quite heavily, aren't I? Tell me it is. It's considered to be, I mean, I understand you study invertebrates. I guess, I mean...

From our point of view, it's important because it's how we eat. So you could come up with some reason for deciding from your point of view that it's important. But evolution actually tells us that it's important. In that, we came from fishes that didn't have jaws.

And of the fishes that emerged from that jawless ancestor, there are only two tiny branches that don't have jaws and tens of thousands that do have jaws. So the jawless fishes are the cyclostomes, so the lampreys and the hagfish.

So two tiny, tiny branches without jaws survived and then the ones that evolved jaws took over the world and gave rise to almost all the vertebrates that still arrive today. So in a sense, that's a natural experiment into are jaws useful or not. Evolution would tell us that it's much better to have a jaw than not to have a jaw because those are the successful species. Sounds it, absolutely. Yeah.

You obviously talked in the book as well about the fact that there's a particular group of cells that appear during development that help build the jaw. These are called the neural crest cells. And you'll forgive me for being a nerd also in this moment, but the neural crest is a really interesting cell type to appear. So not only does it build the jaw, it contributes a lot of cells to building of the whole head structure, not just the jaw, right?

And oftentimes when you ask children, what's an animal or anything like that, describe an animal, they'll describe something that has a head. And sometimes I was struck by that, even reading your book, because you really reminded me at least that the tree of life is so much more than just cats, dogs, cows, humans, the things that we think of immediately when we think of animals.

And so I found myself wondering if you were also slightly advocating for the importance of organisms that maybe don't just have like classical heads. Is that something that was in there? - Absolutely, absolutely. So I'm an invertebrate biologist. So for me, vertebrates all look the same. So you look like a fish from where I'm standing. - Fair enough.

I've talked about these phyla, these distinct body plans, and the vertebrates are one part of the chordates, which is the phylum. So vertebrates are a tiny twig, and there are about 30 other phyla, which are just as unique and important and different as the vertebrates are.

So, you know, I've talked with, you know, there's familiar things like arthropods and mollusks and anelid worms. But there's 25 others that are sort of known only to geeks like me, the nathostomelids and the rotifers and the, you know, chesignaths, etc, etc. I could list, I could reel off a whole list of them. But that's really where the diversity of animals exists. The virtuots themselves are...

fascinating obviously but um yeah well i mean i just want to zoom out a little bit in that case so um obviously there's lots and lots of fun and fascinating stories and at least for me i was you know the more i got through the book the more i started thinking you know actually

This is a really timely reminder of the fact that we are but a twig on the tree of life. Because, of course, you know, this book comes at a time where there's all kinds of stuff going on on our planet. One of which that is particularly relevant, I think, to this context is, of course, climate change and the changes that are happening in our physical environment. And it's so easy for all of us to just focus upon, you know, the environment.

the boring chordates and the invertebrates, as you said, when we can think about climate change affecting things. So could you tell us a little bit also about how the change in our environment is affecting the rest of the tree of life that is still with us? Well, I do. I think you're absolutely right. It is an absolute tragedy. And the people who care about climate change do tend to focus on

sea level rises and the effect on humans and human migration, which is all going very likely to be terrible. But there are literally thousands of species dying every year already due to climate change. It's terrible. But I think writing the book somehow gave me a

Very humble, not just as a human, but as a vertebrate or an animal, realising that, you know, we're so recent. We've just appeared, you know, in the last over four billion years. You know, we're the last tiny, tiny millimetre of the ruler of time, if you want.

And whatever mess we make of the world, it'll be just one of a series of horrible catastrophes that has changed the history of the world, changed the history of life. And it'll be a blink of an eye. There might be a terrible human-derived catastrophe, but the world will keep going and the tree of life will keep growing and maybe we'll be a sorry little footnote on it.

Gosh, I feel like that's quite a good moment to sort of stop, to be honest. Is it a positive humbleness that you're feeling?

I, yeah, I guess maybe it makes me, I mean, I, you know, I feel very sad for the generations to come. I've got kids and, you know, hopefully one day grandkids and I think they're going to be badly affected by it. But on a slightly longer timescale, I think, you know, it's a, it's such a tiny period on the history of life and one, one's, you know, single species have been responsible for,

huge changes to the climate before. There's something called the Azolla catastrophe, which was an ice age caused by this plant growing around the Antarctic that sank in huge numbers to the bottom, drawing down masses of carbon dioxide. It wasn't as quick as we've been, but we wouldn't be the first species to make a mess of things. Well, I've never heard that before, Max. That's fantastically interesting.

And you're right, perhaps slightly relieving. Okay, well, on that note, I should thank Max for his time. That was Max Telford, the author of The Tree of Life, which you can see here, available now online or at a bookshop near you. I've been Ganesh Taylor, and you've been listening to Intelligence Squared. Thank you for joining me.

Thanks for listening to Intelligence Squared. This episode was produced by myself, Mia Cirenti, and it was edited by Bea Duncan. You've been listening to Intelligence Squared. Thanks for joining us.

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