Instant Genius - Neil Shubin: How do big changes in evolution happen?

Episode Date: May 4, 2020

The first time a fish crawled out of the water and onto land, it was a turning point that led to brand new kinds of life. But this couldn’t happen on its own: that fish would have needed both lungs and legs. Neil Shubin, evolutionary biologist and author of Some Assembly Required (£18.99, Oneworld), says that fish didn’t evolve these traits to help them live on land. In fact, the reason they could live on land was that they repurposed the body parts they had already. The same remarkable changes have happened all through evolutionary history, from the first vertebrate life to the first flying dinosaurs. He speaks to our Online assistant Sara Rigby. Read the full transcription [this will open in a new window] Let us know what you think of the episode with a review or a comment wherever you listen to your podcasts. Subscribe to the Science Focus Podcast on these services: Acast, iTunes, Stitcher, RSS, Overcast Listen to more episodes of the Science Focus Podcast: Ross Barnett: Why should we be interested in prehistoric animals that aren’t dinosaurs? Brian Switek: How did bones evolve? Steve Brusatte: The truth about dinosaurs Neil Gemmell: The genetic hunt for the Loch Ness Monster James Lovelock: What can the father of Gaia theory tell us about our future? Andrew Hunter Murray and Dan Schreiber: Is there really no such thing as a fish? Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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So you can experience exceptional sound at home. Music just as the artist intended. Visit name audio.com to learn more. When you think about that, you could say, well, you know, how did fish evolve to walk online and wouldn't they need limbs and lungs and all this other stuff to arise simultaneously? And the answer was, no.

It's the Darwinian vision. That is, lungs existed for eons before creatures took their first, our distant ancestors took their first steps on land. Arms existed for millions of years and legs existed for millions of years before the creatures took their first steps on land. Fish living in aquatic ecosystems 380 million years ago or so already had lungs, already had fins with arm and leg bones inside. And they were using these features to live in water, such that when they were,

the opportunity to invade land happened, they already had this stuff. You're listening to the Science Focus podcast from the BBC Science Focus magazine team. With the UK's bestselling science and technology monthly, available in print and in several digital formats throughout the world, find out more at sciencefocus.com or look out for us in your app store. Hello, I'm Alexander McNamara, and this week's episode is all about the big evolutionary leaps in the history of life. The first time a fish crawled out of the water and onto land, it was a turning point that led to a brand new kind of life.

But this couldn't happen on its own. That fish would have needed both lungs and legs. Neil Schubin, evolutionary biologist and author of Some Assembly Required, says that fish didn't evolve these traits to help them live on land. In fact, the reason they could live on land at all was because they repurposed body parts they already had. The same remarkable changes have happened all throughout evolutionary history, from the first vertebrate life to the first flying dinosaurs. He speaks to our online assistant, Sarah Rigby. So first of all, can you please just tell us a bit about what your book is about?

So my book's about evolution, the history of life. How did the great variety of creatures we see on Earth today come about? And, you know, scientists have been thinking about this question for centuries, but we're at a really critical moment where new technologies, from genome science to developmental biology, as well as the technologies that we analyze fossils with and discover fossils with, it's really changed. And it's really given us a new window onto some of the classic questions of biology. You know, how did some of the great evolutionary changes in the history of life happen?

How did a fish evolve to walk on land? How did birds evolve to fly? You know, how did those apparent impossible leaps happen? Well, I mean, new technologies are giving us new answers. So why do we need to still study evolution? Didn't Darwin figure it all out with his survival of the fittest? You know what's remarkable? is Darwin in 1859 in his first edition of the origin, we went through about six of them,

laid the groundwork for some game-changing ideas, obviously, in how we think about the diversity of life on Earth. There's a before-Darwin time and an after-Darwinian, pre-and-post-Darwinian. The reality is he came up with this notion before we had any knowledge of genetics, of heredity, let alone DNA. And so it's interesting to take the Darwinian vision

and think about it in a sort of in a DNA framework, in a molecular biology framework, how does it comport with the molecular evolution we've lived with for the last 30 years? And it's really remarkable because, you know, some of his ideas apply very well. Others are fundamental. Still others, not so much. And so it's very interesting to sort of see how the Darwinian view plays out, you know, in this new world of genetics. And the thing about it is it plays out extremely well. But there are tons of surprises. So one thing I found really interesting was the story in your book about St. George Jackson Mivet and how he influenced Darwin's theory. Could you tell us a bit about that, please? Yeah.

So sometimes great people are pushed by their greatest foes. So Darwin published the first edition of the Origin of Species in 1859. and it was, he realized it was, it was not entirely complete. Well, you know, he had enormous detractors at the time and supporters, but one of the people who was most influential in sort of pushing Darwin to greatness was Mavart. And he was just the ultimate contrarian in his personal life, in his scientific life. I mean, he'd love to just disagree. You know, he changed his Anglican faith to Catholicism and his youth really upset his parents and also upset his prospects for getting into Oxford and Cambridge at the time.

He was originally a Darwinian, but then turned on it and wrote a very influential critique of Darwin in a book he called On the Genesis of Species. You know, I mean, just that one word variant of the Darwinian title was pretty remarkable. But he basically said, you know, look, you know, how do these, how did birds evolve to fly? You know, I mean, the number of changes that have to happen for birds to fly. are just impossibly large. Then they'd have to happen simultaneously. They'd have to have feathers.

They'd have special lungs, special types of metabolism. And the same is true for every great transition, whether it's the origin of creatures that walk on land. They have to have lungs and legs and arms and necks and all this sort of stuff. And basically, he wrote a challenge to Darwin. Darwin then in the sixth edition of the origin of species, he's about five years later, really responded to Mavart in a very important way and came up with and solidified one of the foundational ideas that we use when we think about the great transitions

in the history of life. And you said, you know, look, you know, the biggest changes aren't always the origin of new structures. It's a change in function of structures that already exist. It's repurposing and modifying things that already exist. And he, in that response, really, sort of set the stage for a new way and an important way and a very modern way of thinking about these great transitions that it's not always the origin of a new structure or a new gene. It's taking what exists and finding new functions for them. And what that means is that organisms have at every stage a range of features, genetics, genetics and development in their anatomy. And they vary a lot and considerably. And they have a reservoir of this variability so that when the opportunity

arises, they can evolve in new ways. One of the signature exemplars of this is the transition from life and water to life on land. You know, you think about, something that I've been working on for a number of decades, when you think about that, you could say, well, you know, well, how did fish evolve to walk on land? Wouldn't they need, like, limbs and lungs and all this other stuff to arise simultaneously? And the answer was, no.

It's the Darwinian vision. That is, lungs existed for eons before creatures took their first, our distant ancestors took their first steps on land. Arms existed for millions of years and legs existed for millions of years before the creatures took their first steps on land. Fish living in aquatic ecosystems 380 million years ago or so already had lungs, already had fins with arm and leg bones inside. And they were using these features to live in water such that when the opportunity

to invade land happened, they already had this stuff. And basically they just changed the function. from walking in water bottoms, you know, in the bottom of the water column to walking on land. From using lungs to breathe in water that might have low oxygen, they use them to live on land. So again, change in function. Right, yeah, that's a really weird thing to think about. Why would fish have evolved lungs in the first place? Yeah, so this was known for a long time before Darwin, actually.

originally Jefferson Toulogne discovered this and the others that had inferred it before. So when you think about the, so basically if you look at fish, they have a gut tube, right, the mouth and the digestive tract. But lying adjacent to the digestive tract in the thoracic area and what's the equivalent of the chest area, right, in the fish equivalent of that is typically an air sac that is related to the gut tube that develops from the gut tube. that sack in many fish serves as a swim bladder. It's a like a bladder that serves for neutral buoyancy. And a lot of other fish, that sack is vascularized, and when it's filled with air, can serve as a respiratory organ, and that's a lung. And it turns out many fish have this lung. So how do they use the lung?

Well, the fish that have lungs, and there are living exemplars of this today, have lungs, but they also have gills. And they use both to breathe. when there's plenty of oxygen in the water, they'll typically use the gills, just like most fish. But when the oxygen level in the water decreases to a certain point, as it does in many freshwater systems throughout the year, they'll rely more increasingly on the lungs, and they'll just go up to the surface, take a few gulps of air, and then go back down. So lungs are sort of an accessory organ for breathing when the oxygen levels go down. It turns out they turned out to be a fabulous organ when this is when fish decided to make that

commitment to life on land. And then the same thing, by the way, applies to arms and legs. You know, fish had arms and legs inside their fins for millions of years before any critter took the first steps on land. And they were using them, we think, to walk on the bottom of the water like a lot of fish do today, to station hold, to grab the bottom and wait there as the current brings by prey for them to snap up. Or sometimes even to live in the shallows, you know, in the mudflats and so forth. So, you know, fish evolving in these aquatic ecosystems already had important evensions that when the shift to land came, all they had to do was just change the function of stuff that already existed. So another example of this that I think you mentioned is the evolution of flight.

So when dinosaurs were evolving feathers, which was quite a controversial idea, could you tell us a bit about that, please? Yeah. So, you know, the traditional view of dinosaurs from about a century ago was these giant lumbering beasts. And that view really changed dramatically starting about three decades or so when people started to realize that dinosaurs, particularly theropod dinosaurs, the carnivorous ones, were fast-running, high metabolism, rapid growth rates, had hollow bones. And in fact, many of them had most derived ones, had bird-like structures, had forearms that looked something like wings, had a version of a wishbone.

All of a sudden, you know, they looked really bird-like. And then, starting in the mid-late 1990s, coming out of China, where at first they were reports, just like whispers. And then it became real that there are dinosaurs with feathers discovered in the fossil record. And for what was originally just one or two species with feathers, we now see almost all these carnivorous dinosaurs had some sort of. of feather-like structure outside them. So just like lungs and the origin of limned animals, feathers predate the origin of flight. And we believe that feathers are used for courtship displays like in birds today, and initially perhaps in thermoregulation, you know, serving as insulation,

but they weren't used for flight. You know, and so again, it's a change in function. That Darwinian quote, you know, in his response to Mavart, is just so perfect. You know, it's, it just explains, you know, how you can get great change. without having to wait for mutations to occur independently throughout the body. Creatures already have these things. Right. So yeah, that's quite an important distinction, isn't it? So it's not that dinosaurs evolved feathers to fly, but they evolved feathers and that helped them to fly. That's right. They evolved feathers to live as better dinosaurs. You know, not to fly. And likewise, lungs, you know, fish evolved lungs to be better fish. And it just so happens later on, that was really great when fish started.

to walk on land or when dinosaurs needed to fly, you know. And so that's the, I think that's the same point. And what's neat about that point and what's so foundational about it, you know, when you think about how Prussian Darwin was, was that it applies equally well to when we think about genes and how they come about. Like the, that it's not always the evolution of new genes that matters. It is in some cases. But in a lot of cases, it's not the evolution of new genes that really matters. It's finding new uses for genes that already existed, redeploying them in new ways. and a new context to make new stuff. Can you give us an example of that, please?

Oh, yeah. One of the great examples of this is the one of the changed my life, right? So, starting in like the, when molecular biology tools became ever more powerful, it was discovered that certain genes play a very fundamental role in building bodies. And I think the interest in these genes started before we knew anything about DNA. It started when people were really looking at flies as a model for genetics, fruit flies, and they were cataloging different kinds of mutants. And these folks working in the fly lab in Caltech, Columbia University, and elsewhere, found just mutants that were just head scratchers. They would find, say, fly with a leg where an antenna should be.

Okay, so in the head, there was a leg sticking up the head, okay? I'm thinking about that one. Or they found a fly, a free fly that had two body segments, the held wings instead of two wings. instead of two wings, it had four. They call it bithorax. The other one was called antennapedia. You know, so leg were intending. So these were like flies that had like the right body parts, but the body parts, they

somebody cut and pasted them, you know. They were in the wrong place. So these mutants captured a lot of people's interests such that when the DNA technology became ever more powerful and this started in the early mid-1980s, folks discovered the actual bits of DNA that encode for those genes. and they discovered that there is a whole catalog of these kinds of bodybuilding genes that control when and where organs develop in the body. And not only do they find these genes in flies, but they found that versions of these same genes are making the bodies of everything from chickens to mice to people. So here was a fundamental toolkit that builds the bodies as different as flies and people.

And I remember when that set of discoveries came out in the mid-late 1980s. I was training to be a paleontologist, and I saw these discoveries. They were published in nature and PNAS and elsewhere. And I looked at them and I said, okay, I need to learn a little molecular biology here. I was like that was that important. So I, and so when I think about, like, getting it back to Darwin's quote to your question, I've taken the long way to get to your question, but where you're getting to it. So basically you have these genes.

The trick here is that these genes, are involved in patterning the body, but they're also involved in patterning parts of the limb. They're involved in patterning parts of the brain. So what you're seeing is these genes arose for one purpose to pattern the body axis, the general body plan. But then they were co-opted or redeployed to make appendages, to make parts of the head and so forth. So it's like once you have one tool, right, one recipe, you can redeploy that recipe to make other things. So again, it comes down to sometimes the, the, the, biggest shift is not in evolution, you know, new, making new genes, but is using old genes in new ways.

Another way we see that happening is in how sometimes new genes actually come about. When new genes come about, oftentimes, although not exclusively, but often, they come about as duplicates. Their gene copying gone wild. So what we see is whole families of genes in our genome that are related to one another, and they evolved by copying, duplication. of our genetic material. So of these body building genes, you know, flies have like sort of one cluster of these things. We have four, you know, so much more complexity. So we find gene duplication is a very common event in the origin of new genetic material as well. So again, using the old to make the new, repurpose it, change its function, or copy it and modify it.

So I always assumed that if you were trying to, say, piece together the evolutionary history of life, That would basically just be fossil hunting. You'd go out and you'd find a fossil, and then you'd have a look at it and see where it fit in, like putting a puzzle piece in the puzzle. But actually, it sounds like there's a lot that we can learn from animals that are alive today. So what can we learn from living animals about their ancestors? There's an enormous amount. So we are so fortunate now that not only do we have fossils, but pretty much the bodies and the genes and the DNA of every creature. alive today is a library of its evolutionary history. That is, every creature alive today,

inside its genomes, inside its cells, inside its tissues, contains artifacts of billions of years of the history of life. And the trick is, how do we know how to unlock that? And we see that vividly, you know, with each new genome that we discover, that we read about. You know, we have the human genome project, the Rice genome project, the Lilly. genome project, the corn genome project, genome projects for thousands upon thousands of different kinds of species. You know, we get them with ever increasing frequency. And what we've learned is now to compare the genome in many important ways, not just the sequence of DNA, but the structure of DNA as well. And when we do that, we can start to ask some really important questions. So we have a

knowledge of the chimpanzee genome. We have a knowledge of the human genome. We have a knowledge of all kinds of fish genomes and on and on and on. We can begin to ask the question at the level of DNA, what makes a human different from chimps? What genes are important? What are the processes that are important in making distinctively human features? We could take the question back even further. We can compare the genome, the human genome, to that of a fish. And we can ask, what's the same and what's different?

What's different about the genetic recipe that builds the body of a fish, like live today, from the genetic recipe that builds the body of a human or a chimpanzee alive today. And so these are questions that were formerly the domain of fossils or comparative anatomy. Now we can unlock them with the knowledge of the genome. In your book, you have this diagram that compares the embryos of lots of different species of animal, quite wide-ranging species and at different periods through their development. and early on, they all look really strangely similar. Could you tell us a bit about that diagram and the implications of that, please?

Yeah, so that diagram is a version of one that was done by Carl Ernst von Berer, who was an embryologist who lived decades before Darwin. And he was interested in asking the question, you know, how does the development from egg to adult of critters as differing as turtles and fish and mice, how do they differ? And so he was collecting lots of embryos and storing them in vials, so he'd have these different embryonic stages of different embryos, and he'd put them in vials with alcohol or formalin,

and to preserve them, to preserve them, because he'd look at them under the microscope, but he forgot to label, or I believe the labels fell off a few of his vials, fell off a vial that contained, you know, so he had like turtle and mouse and fift, embryos in these vials, but he knew that they were, but he didn't know which was which. And he couldn't tell them apart because they were all early embryos. And so this sort of led him to think about, you know, his theory and his idea is one of sort of differentiation. That is,

early embryonic stages of critters of different species tend to look much more similar than do later embryonic stages. And that's what you see in that diagram. I mean, I put a version of his, which is, you know, turtles and mice and fish and birds and so forth. And early embryonic stages, you know, you might find some differences, but they tend to look extremely alike. And then they acquire those differences later in development. And that was really important. And then a version of the same sort of theory altered a bit came out after Darwin published

the origin of species. And it turned out to be wrong, and not a good generalization, but it's a very good generalization, but it's stimulated an enormous amount of work. And that was the notion that by Ernst Heckel, which was the famous one, ontogeny recapitulates phylogeny. And by that what he meant is development from egg to adult ontogeny,

recapitulates phylogeny, which is evolutionary history. So his theory was, it's very different from von Beres. His was basically, if you looked at the development of any species, it will track its evolutionary history.

So if you looked at a human embryo, you'd see it go through, it would go through like a fish stage, an amphibian stage, and a reptile stage, and so forth and so forth. Well, you can imagine, oh, and also, Heckel was an amazingly good and talented artist as well. And so his book was just rich with illustrations, rich with ideas, rich with conjectures and so forth, and it was enormously influential. Turns out that's probably not a good generalization, that ontogeny recapitulates phylogeny. We see it in some structures, though. Well, like, if you look at the development of our kidneys, there definitely is sort of a, it

track its evolutionary history to some extent, as well, some other structures, but it's not like a law of nature like what he wanted to, and what he wanted to propose. But honestly, I think where Heckel was most influential was really in stimulating an interest in studying embryos as vehicles to understand evolutionary history, even though his particular theory is wrong. It stimulated so many others to think about embryos in new ways. and so he was important, just like Mavard actually, in being wrong, and how it's stimulated, you know, really a foundational work by others. So why is it that all of these species look so similar, so early in their development? Well, remember, I mean, one thing we've learned in genetics is a lot of them have similar kinds of genes. You know, so when I said that flies and fish and turtles and mice and birds and people all have versions of the same genes building their.

bodies, what we find is it's not only even just the same genes, and sometimes it's whole networks of genes that interact with each other during development. So to some extent, I think it's reflecting history. You know, I mean, it's reflecting the fact that these creatures have similarities, getting back to Darwin, that the reason why they have these similarities is that all of them shared a common ancestor sometime in the distant past, you know, and some of them shared very distant common ancestors, some of them share more recent common ancestors, but common ancestors they all share. And so we're seeing that as a reflection of this common ancestry. So there are some species which have juvenile states like frogs have a tadpole stage and

things like that. And so could you tell us a bit about how these juvenile states can sort of influence evolution of species? Yeah, hugely. So I mean, one of the most vivid examples of this was Auguste Dumeril, who was the keeper of reptiles and amphibians. at the Paris Natural History Museum in the 1800s. And Dumreel, one of the iconic stories is when Dumreel, who was famous at the time, and he became a Darwinian. After the 1859, the first edition of Darwin, Doomreel was enthusiastically a Darwinian. And he was famously so.

So people would send him specimens from around the world. And one day he received a box from colleagues who were working in Mexico, and it was a box that contained a handful of salamanders, fully grown adults. And the reason why they sent them to Dumreel was these fully grown adult salamanders were also aquatic. They had external gills. They had big, like, fleshy limbs that looked a little bit like fins. They had a tail that had a big fold on it, like fin-like sort of thing.

Lots of like aquatic features in a sexually mature adult salamander. So Dumreel thought, well, I'll just study these. Maybe it could tell us about, give us insights into the transition from fish to, land-living creature. So, Dumariel, but then he got busy with other things. So he stored these things in his enclosure, would feed them, and then came back at one point, and he found two different kinds of salamander in his box. He found at one point he had full adult, the ones he was sent, the ones with the external gills and all the aquatic traits. But then, living right next to them were

other salamanders, fully grown aquatic, fully grown adults, but these had no external gills. These were fully terrestrial. They had fully terrestrial limbs. They had no fin-like tail, not the flipper-like tail, none of that stuff. So it's almost like some, he put like chimpanzees in a cage one year, came back eight months later and found chimpanzees and gorillas, you know, happily living together. He's like, what is going on in my box? So that stimulated doom real to think about larvae. And so doom real and others started to think about, you know, let's look at the life history of these things. what happens from egg to adult. And he found, as your question suggested, that the importance here is what happens to the larval stage.

So as we know, in tadpoles, you know, tadpoles hatch from the egg, they swim around as larvae. And those larvae, the tadpoles are aquatic, and they have aquatic mechanisms. They swim around. They feed in water with suction feeding and so forth. Then something happens, you know, a surge in, usually in the thyroid hormone. and then they undergo metamorphosis. And in metamorphosis, as we all know, they go from a tadpole to a frog,

their legs change, their skull changes, their whole body changes, and they become jumping frogs. Well, the same thing is true as salamanders. They go through many species of salamanders, although not all, will undergo, they'll have aquatic larvae,

they'll swim around, live in water, undergo metamorphosis, and then become fully terrestrial adults. What Dume Real found is that metamorphosis is optional. And it can vary. And so that, you know, the species that are fully terrestrial undergo metamorphosis, the ones that were those,

you know, fully aquatic adults, they did not undergo more metamorphosis. There was a simple shift that happened in their endocrinology and their hormone levels. A very simple one. And that simple hormonal shift led to changes across the entire body, which would have been, you know, just an enormous amount of genetic change, if it would have to happen otherwise. So we found that you can have through simple shifts of development, enormous changes to the bodies of critters. And so those two different kinds of salamanders just came about from just a simple,

you know, whether you metamorphos or not. And it turns out that those kinds of properties are important for evolving systems more broadly, from invertebrates to other kinds of creatures. That is one very fundamental way of evolving. is by changing the timing of developmental events, stopping early or stopping later, slowing things down or speeding them up, the more you do that, the more you can have changes that are coordinated across the entire body. And that was work that was stimulated largely by Dume Reel and the people that followed him.

So there's an example of this sort of, you know, changing of the speed of development that really surprised me. And that was the example of the sea squirt. Could you tell us about how the sea squirt led to, you know, vertebrate life? Yeah. Well, I mean, one of the, you know, when you think of vertebrates like us, right? So, you know, where did vertebrates with backbones and skulls and skeletons come from? Well, if you look at that and you try to trace that in terms of comparative anatomy, there are three traits that are seen in early development that all vertebrates and their closest invertebrate relatives have. And that is, they have a number of. nerve cord that runs along the back.

It's called a dorsal nerve cord, hollow nerve cord. They have gillslitz in the pharyngeal area. And they have a supportive rod called a notacord. So those three traits, when I teach intro, bio, I teach, these are the three fundamental traits of the vertebrate body plant, and there are a number of, you know, invertebrate creatures that have them. They're our closest relatives. And so we talk about those.

So people have always asked, you know, where do vertebrates come from, you know? And there's lots of really interesting living creatures alive today. There's one called Amphioxus, which has a beautiful aspect of the vertebrate body plan, even though it's not a vertebrate, but it shows what they're derived from. But others, some Russian biologists as well as Garstang, who was a great biologist in the UK, came up with a different idea. That is, that the closest relatives of vertebrates, they proposed, were the oddest looking ones.

So Garstein, Walter Garsting, was his name, came up with the idea that, building on what Russian biologists did a few decades before, that the closest relative to vertebrates looked something like a sea squirt. That is, a sea squirt, to paint a word picture, a sea squirt is something that does not even look alive. It's like basically they're these sessile animals attached to rocks.

it looks like a formless lump of clay. If you were to take a peek at it, it has like a hole at the top and they pump water. But there's no obvious head, no obvious body, no obvious tail. There's no obvious nerve cord, no obvious cartilage rod, that note of cord I was telling you before, let alone gillslitz. There's nothing there. But yet Garstang believed that they held the secret because he knew something about development. He knew something about embryology. because if you look at sea squirts,

they don't start their development like that. What they start like is they are hatched from an egg, and the larval sea squirt looks something like a tadpole. It has a head and a long slender body. It swims around in the water. And when he looked at the tadpole, what do you see? It has that nerve cord. It has that cartilage rod called a notocord.

And it has the gillslits. And what happens is these little larvae swim around, And at some point, they decide, okay, it's time to settle down. And they swim to a rock. They attach to the rock. They proceed to lose the tail, lose the head, lose the notocord, lose the nerve cord, lose most of the gillslits, and change their body to become this, you know, this formless lump of clay with a little hole on top. And so basically what Garstang said is, well, the shift to vertebrates was real simple. You begin as a larval, a larval tunicate animal.

And then don't metamorphose. You know, so basically stop early and then just grow from there. And so there's a case where, you know, putting the, you know, stopping metamorphosis, not undergoing that metamorphosis, and just continuing development from there, it was a likely big part of our own distant evolutionary history. So that's a really weird example of something that's happened in our evolutionary past. What is your favorite thing that you've learned about from this book, evolutionary quirk like that.

What's your favorite one? My favorite, so one of my favorites is, I have so many, so it's hard to choose one. It's like, you know, you're asking which my children are like the most. But, you know, it's hard not to love salamander tongues, to be quite honest. So, and not all salamander tongues, but most. So one, you know, there are two kinds of animals in this world. They're animals that bring their head to the food, think lions and cheetahs. Then there are animals that bring the food to their head.

head, I think salamanders living on land. So some salamanders living on land have evolved a really amazing biological machine and that it's a machine to project their tongue. They snap out their tongue about almost the length of their body in less than a millisecond and they catch an insect and bring it all back. I mean, it's just an amazing biological machine that they shoot their tongue out ballistically like a missile, attaches to an insect and just as fast brings it back into their mouth. And for that to happen, it takes lots of changes. It takes changes to the Gill apparatus. It changes the muscles of the body. I mean, you're inventing a whole new machine with lots of different parts. It turns out that that machine with lots of different parts likely came

about two to four times independently in the history of salamanders. So this amazing biological machine was attained multiple times independently, the more we, you know, study the DNA record. We see that. And it just shows an example to me, which I think is very important. in evolution, that is oftentimes, in fact, more often than not, there is not just, you know, one pathway to something. There is multiple pathways, evolutionary pathways, to the same invention that we find is in evolution over and over again, the independent origin of the same invention in distantly related species, you know, and I think that's the more we learn about genetics and

development, the more we learn about how, you know, how animals function as machines, the more we see that these limited number of solutions are hit upon again and again, and that's telling us something very important about the nature of evolution and biology and so forth. So salamator tongues, love them. That was Neil Schubin talking about how big evolutionary changes really happen. His book, Some Assembly Required, is out now. If you haven't already, make sure you look back through our podcast feed and listen to our special news series, which we've called everything you wanted to know about, where we get a world-renowned scientist to answer your questions. In the first series, we get Professor Jim Al-Khalili to answer the big questions in physics.

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