Neil Shubin, a paleontologist and evolutionary biologist at the University of Chicago who studies how new features arise in lineages of animals, is famous for his discovery of Tiktaalik roseae, a transitional fossil that marked the movement of four-legged animals onto the land. In this conversation with host Steven Strogatz, he discusses how to deduce where to find fossils of long-extinct creatures, why salamanders have such unusual tongues, and what the history of technology can teach us about evolution. This episode was produced by Dana Bialek. Read more at Quantamagazine.org. Production and original music by Story Mechanics.
Steve Strogatz: Were you a scaredy cat or brave?
Neil Shubin: Oh gosh. No, I’m not a brave guy. I am somebody who has led expeditions to Antarctica, to both polar regions, to Africa, to China. And I am the person, if you met me in high school, I’m the least likely person ever to camp, okay? Let alone lead expeditions. I didn’t camp until I went on my first fossil expedition in my first year of graduate school.
Steve Strogatz [narration]: From Quanta Magazine, this is The Joy of x. I’m Steve Strogatz. In this episode, Neil Shubin.
Shubin: And so, now, yeah, I camp out near minus 40 degrees in Antarctica and lead expeditions there, but it wasn’t in my natural toolkit. Let’s put it that way.
Strogatz: I mean, Neil Shubin is a man of many hats: a biologist, a paleontologist, a geologist. He’s interested in the deep history of the earth and the life on the Earth. He is especially renowned for discovering some transitional creatures — in particular, one that we think of as helping us understand how life made its trek from the sea to the land.
Shubin: I went to graduate school knowing I wanted to do paleontology. Because before then, I was interested in all sorts of historical sciences. I almost went into cosmology, astronomy. I loved, you know, how you could link an understanding of the mechanisms of the cosmos to understand its history. I also loved archaeology as well, for different reasons. So I went to graduate school to become a paleontology — to become a paleontologist, but I didn’t know what I wanted to study. I had sort of an inkling that I might want to study mammal evolution because there are a lot of great puzzles and problems there.
So I took a class, and it was kind of like a “greatest hits in the history of life.” And every week, we would hear about a different great transition in the history of vertebrate life. And I remember — this was somewhere in the beginning of the class — the professor showed a slide.
And it showed a fish on top, like a cartoon of a fossil fish on top, and it showed an early limbed animal, an early tetrapod on the bottom, and it had an arrow connecting them. And it showed all the differences, you know, between the fish and the land-living animal. You know, and there were differences in the head. There are countless differences in the appendages, you know, from fins to limbs. There just is a long list of changes there.
And I remember thinking, ‘Holy cow, that is a first-class scientific problem.’ I mean, how did fish evolve to walk on land?
And I literally had the bug right there. And I started to dig into the literature and see what we knew and what we didn’t know. And there were some fossils that were somewhat intermediate. But I’m thinking, yeah, we do a lot better. I mean, think about it: You know, how do you go from a fin that’s used in water, to a limb, which a creature walks on land? How do creatures evolve to breathe on land, to live their lives? It just seems like a giant revolution. So off I set…
Strogatz: Well, I mean the courage and the nerve, the chutzpah.
Shubin: Interestingly, you know — and again, just this is sort of kismet. I was with —. The senior professor who was teaching it was one of the world’s great field expeditionary vertebrate paleontologists. He had already gone off to understand the origin of mammals, like working in Arizona, working in a Colorado, Montana, and so forth, and he was finding some great intermediates between reptiles and mammals. And he had a simple toolkit that he was using. And I thought, well, golly, I can deploy that tool kit to understand the origin of tetrapods.
And so I was sort of … was sent off to deploy the tools that, the conceptual tools he was using to find early mammal ancestors to this problem of the fish-to-tetrapod transition. You know, if you’re a paleontologist and you want to, you know, find an important fossil that tells you about a great transition in the history of life, you know, you look for places in the world that have three things. First, you look for places in the world that have rocks of the right age to answer whatever question interests you.
Shubin: Right? So if you’re interested in the origin of mammals, you’re gonna look at rocks from, you know, late Triassic, right, 210 million years old. If you’re interested in the origin of tetrapods, like I am, you’re looking into the Devonian. That’s in rocks that are about 380 million years old, 370 million years old.
Strogatz: Let me have you pause there for those of us who aren’t all plugged into these different ages. I mean, that’s already an interesting bit of detective work that, I take it, that you sort of see in the fossil record there are things that really look like mammals after that time and there really aren’t things that look — or, sorry, not mammals, tetrapods, these four-legged critters. You see them after this time, but you don’t see them before, so you know, somewhere in there. Is that the reason?
Shubin: That’s correct. No, that’s exactly right. So 150 years of paleontologists going around the world, you know, finding stuff has really give us a timeline where the first fish appear in the fossil record before the first limbed animals. The first ancient limbed animals appear in the fossil record before the first reptiles. The first reptiles appear in the fossil record before the first mammals, and on and on and on and on.
And, you know, you can begin to leverage that to ask all kinds of questions. So I begin already having a timeline that other paleontologists, you know, have exposed over a century and a half of paleontology research.
Strogatz: Yeah. And that’s actually something I love about the collective enterprise of science that, you know … with Newton’s remark about building on, or standing on the shoulders of giants, clearly, you’re doing that. Right? You say there’s all these — there were things that were known from your predecessors. And as you say, it’s sort of like recapitulating that there’s this historical science of evolution that studies the history of life on earth. You get to use the history of discovery to know where to look, or I should say when to look, what rocks of what age are gonna have —?
Shubin: That’s correct. That’s correct. And you gain a — I mean, you almost become like a historian of science in some cases for some of these fields because you need to understand the challenges and the struggles that your predecessors had. And oftentimes, they were struggling, albeit with different technologies [LAUGHTER] with some of the same questions and some of the same problems.
So in this case, I already had a timeline, a crude one that I could use. And so I was looking for places in the world that have rocks of the right age. Then the next thing you do — and again you’re standing on the shoulders of giants, just like you said — we’re looking for places in the world that have rocks of the right type to hold a fossil. Not every kind of rock will hold a fossil for a variety of reasons.
You can think about volcanic rocks. Right? They’re formed in lava. That’s not gonna hold fossils. You have rocks that are metamorphic, that are squeezed under high pressures and sometimes very high temperatures. Those will destroy whatever fossil is inside. Furthermore, you may have places in the world where the creatures didn’t live.
So you have to really think about what kinds of rocks, what kinds of environments that were in those rocks, that those rocks represent, would likely hold the creatures you’re looking for. You know? And here we’re building on all kinds of science projects that have been done over the last hundred years. Countries, oil and gas discovery firms, extraction industries…
Shubin: They map rocks in different parts of the world.
Shubin: That’s how you find — you look for places in the world that have rocks the right age, rocks that are the right type to hold fossils, and rocks that you can access. And that’s the way we turn a giant globe into a small number of places to look for fossils.
Strogatz: That in itself is so interesting to me because there’s that old joke about the guy that’s looking for his keys under the, you know, the lamppost at night. [LAUGHTER] Right? Late at night. And they say, “Why are you looking there? Did you lose them there?” And he says, “No, but that’s the only place where the light is any good.”
Shubin: Well, my lamppost is where countries have decided to invest to map the rocks. Right? I only know those places where countries have made those investments, or companies and so forth. So, yeah, we started in Pennsylvania. I began with a graduate student by the name of Ted Daeschler, who’s now — I’ve worked for him for 30 years. He’s now a senior curator in Philly. And we started finding these fossils. We found early tetrapods. We found lots of lobe-finned fish that are closely related to these tetrapods on road cuts in Pennsylvania. Because these were rocks that were 365 million years old. These were rocks that were formed in ancient delta systems 365 million years ago. When the state looked like, you know, the Amazon.
Strogatz: Let me — sorry, I’m not sure I know this term “road cut.” Is that like they blow a hole in a mountain or something?
Shubin: Yeah. It’s like they blow out a side of a hill. So basically, when you drive along Route 80 across the state in northern Pennsylvania, or in the New York State Thruway up near where you are, you’re gonna see cliff walls of rock. And those are actually made by the Department of Transportation when they widened the roads, when they made the thruway or the highways. They would actually detonate. And they would create these cliffs, and then they’d create piles of rock that they removed from — you know, to make those cliffs or to extend the roads, they’d create piles of rocks, far out where they would dump them. And they would bury those, and they’d cover them with, like, vetch and the plants would grow around them.
But if we got really lucky, we would find a place where PennDOT widened the road in Devonian-aged rocks, where they blew up live Devonian rock and created piles and piles of Devonian rock and cliff faces. And we’d look at both of those. We’d look at the cliff faces, and then we look at the piles of rock on the ground.
And golly gee, there were fossils all over, all over. We found fossil fish of — you know, fossil sharks, fossil insects, fossil plants, some early tetrapods. It was a field day. It really was. This was the early nineties. And, you know, three hours from my home in Philadelphia, we had a remarkable window into this ancient world. And this ancient world was when life was coming onto land. You know, you had plants coming first, and invertebrates, and then later our distant relatives. There’s just a whole world trapped in there. And I gotta say, aesthetically, one of the things that really strikes you, I was cracking the rocks along a road in Pennsylvania, and I’m finding tropical plants and big monstrous fish that are about 15 feet long. [LAUGHTER]
Strogatz: Wow. [LAUGHTER]
Shubin: And this just bizarre lost world of critters. You know? And trucks would be whizzing by honking at me. [LAUGHTER] And so, you have this juxtaposition between present and past. Ted and I were like, you know, high-fiving each other regularly, finding wonderful creatures that were telling us about what this ancient world looked like 365 million years ago.
But we realize soon into it that we had a problem. It looked like we were already finding limbed animals, tetrapods that were kind of derived, kind of advanced, and not looking horribly primitive.
Shubin: So we felt we needed to move back in time about 10 to 15 million years. And eventually, we — just a total accident, okay? Ted and I were in my office at Penn, and we’re having some argument about some geological trivia. I have no idea what it was. It’s not important anymore. But to settle the debate, I pulled out my college geology textbook from about 20 years before. [LAUGHTER] Okay? And settled the debate.
And, you know, we’re talking to each other and I’m chewing the fat, turning the pages of the book until I hit a diagram which was to change my life, in a college geology textbook. This diagram was a map of North America and had superimposed on it where Devonian-aged rocks existed across North America, and this excluded Northern Canada.
And the textbook authors identified three areas that had rock of Devonian age that were produced by ancient delta systems — you know, rivers and streams, i.e., the kinds of rocks we’re looking for. There was one patch that they marked in eastern — in central Pennsylvania and southern New York. Well, that’s the one we knew about.
Strogatz: Sounds good. Yeah, but okay…
Shubin: Check that off the list. Been there, done that.
Shubin: Next was up in Greenland, and that was where some of the earliest tetrapods ever known were. Individuals found them in the fossil record working in the ’20s and ’30s in Greenland. And so we knew about that site. Yep, been there, done that.
But then, extending 1,500 kilometers east to west across the Canadian Arctic, were a series of rocks that were mapped as Devonian, mapped as formed in ancient rivers and streams from ancient delta systems. But in this case, they weren’t 365 million years old, they were about 375 [million] or maybe a little bit older.
Shubin: I looked at Ted and he looked at me, and said, “Ted, do you know anybody who’s worked on these rocks?” “I don’t know any. Do you?” I said, “Ted, I just asked you that question.”
Shubin: We went back and forth like [LAUGHTER], “Whoa, nobody’s worked these rocks.” So we ran to the library, which is what you did. This is the mid to late nineties.
Strogatz: I remember.
Shubin: The library. Yeah, remember those things?
Strogatz: I do.
Shubin: Yeah. So we ran to the library and dug out a journal, The Canadian Journal of Petroleum Geology. It had maps of these rocks in the Canadian Arctic. They dated them using some crude methods, but it was clearly the right kind of rock. It was just remarkable. Ted and I were like, “This is our next step.” And I was like, how are we gonna do this? I mean, because now I’m used to driving three hours in my Subaru to central Pennsylvania.
Now, you don’t do that to get to the — these are up in the Artic. These are 500 miles from the North Pole. There are polar bears up there. You know, there’s lots of stuff. I mean it’s a big-time expedition, so it took us a while to get our act together to get there.
Strogatz: But eventually Neil and his team did get there. They made it up to the Canadian Arctic, and they were on the hunt pursuing this fantastic mystery story, looking for this transitional creature that they imagined had to exist.
It had to be some kind of a thing between a fish with gills and fins and a tetrapod. Some kind of four-legged creature walking around on the earth with lungs and limbs. But Neil and his team weren’t just poking around in the dark. They had a very clear idea of what they were looking for and where they might find it.
Strogatz: You go in the summer or the winter, or does it matter?
Shubin: Yeah, it totally matters. So this is the Canadian Artic. You know, the season there is July. So, essentially, you know, we go at the height of summer. And so the height of summer, the sun essentially does a big ellipse in the sky. Temperature, you know, varies. It’s below freezing, but not much. It could be damp and really cold and windy. Wind is just a constant companion there.
Strogatz: So and it’s you and Ted, and how many other people?
Shubin: About six people. We’ve had as many as eight to ten some years.
Strogatz: Should I think like the latitude of some place that I’ve heard of? Like, what’s something in Alaska or up north?
Shubin: It’s north of anything in Alaska. Think about a certain northern part of Greenland, that kind of thing.
Strogatz: Wow. Okay.
Shubin: Yeah. So we’re up there. Yeah, we’re way up there. You know, it’s daylight 24 hours a day. So you have to, god, you realize just how we depend — our circadian rhythms are so deep. So there’s a lot to overcome, a lot of logistics to learn. You know, you have to pack your own food, you have to bring firearms, your camping gear. And the other thing is you have to bring a good attitude. It’s a small world there and can be very intense. And if you’re not finding anything, you have to think about the things that people need to remain focused and happy, and you know, and feeling good about themselves and about the science.
Strogatz: Do I picture you all with shovels, or picks, or hammers, or what?
Shubin: Uh … yeah, hammers. Sometimes picks if we’re cracking into the rock. But, really, kind of, it’s more a day pack filled with emergency supplies, usually a gun strapped to my back up there because polar bears if we’re on the coast. You don’t have to carry water because you can basically … the snow and the ice melt comes right out. I bring a mug [LAUGHTER] which is great. And so we spend the entire day just walking, looking at the rocks, looking at the surface of the rocks, bringing our geological maps, and looking for places where the bones are weathering out on the surface.
Strogatz: I see. So you’re actually just — so it’s not like you’re kneeling and hammering. You’re walking around looking at rocks.
Shubin: Initially. Yep. Initially. We’re looking for where the bones are, and kind of where they’re weathering out. And we’ll find little pods of that. In some cases, you know, you’ll find, you know, a whole skeleton just weathering out. In other cases –
Strogatz: You mean weathering, that means it’s sticking out the side of the face of a rock?
Shubin: Yeah, a little, imagine a cliff, right, or badlands, and you have layers. And one layer might have lots of bone spilling out of it. And you’ll follow those, that trail of bone to the layer that’s producing them, dig into that layer and expose it. And, you know, if you have any luck at all, you’ll find whole skeletons or partial skeletons.
Shubin: So we’re walking around, really kind of looking at the rocks trying to figure out the geology. It’s like a puzzle we’re trying to solve. Where these bones likely to be? And then we’ll, depending on, you know, how fossiliferous they are, we can see spots that have lots of bone weathering out. And that’s exactly what happened here. We brought a college student, Jason Downes, who happened on this layer, which had thousands and thousands and thousands of fossil fragments weathering out of it, just a carpet of bones.
And we traced that carpet of bones to one layer that had — it’s basically a catastrophic event had buried a lot of animals at once, one skeleton on top of the other one. And when it was weathering out, that’s what produced on the side of the hill, that carpet of fragments of bones. But we cracked inside the layer, that’s when we saw skeleton after skeleton piled one on top of the other. And by 2002, we had that layer, and we had a suspicion that what we’re looking for might be in that layer.
So we decide to go back in 2004 because that was our fourth trip after six years of working expedition, and cracking the layer. We started, one of my colleagues was cracking the rocks. We were working the layer. Each of us was pulling out skeletons with different kinds of fish. Then one day, one of my colleagues, Steve Gatesy, who is now at Brown, said, “Hey guys, what’s this?” And I ran over, and sticking out of the side of the hill that he was digging in was the skull of a fish.
But it was very clear that it was a very special fish. That is, you know, if you think about the transition from fish to limbed animal, you have changes in the head, you have changes in the fins. But one of the big changes in the head is you go from a conical-shaped head to a very flat-shaped head, almost like a crocodile. And here I had a flat-headed fish staring out. It was a flat head, clearly a flat head. So I had a tetrapod-like head staring out at me in really old rocks. And so we were pretty clear — it was pretty obvious that we had found what we were looking for. Then we jumped up and down a little bit…
Shubin: And then –
Strogatz: So at this point, just the head is sticking out?
Shubin: Yeah, or actually just the tip of the snout.
Strogatz: Just the snout?
Shubin: Literally the tip of the snout, and it looked like it had a really flat snout. And so we’re looking at it, and I’m saying, “Well, this is just central casting — exactly what we wanted.” Right?
Shubin: I mean, because the rest of the — if we had any luck, whatsoever, the rest of the skeleton would be in that cliff. And it turned out to be correct. I mean, we brought the block home. It was prepared out. And that process took a long time, but that was one of the most exciting time periods of my life.
Ted and I would be on the phone every day. And I’d say, you know, “Ted, what do you see on your end?” And he says, “Well, I see the flat head. It looks — oh, man, it’s just beautiful.” I said, “Yeah, Ted, we’ve got a shoulder. You ought to see the size of this shoulder.”
Strogatz: Wait a second, this is a fish with a shoulder?
Shubin: Yeah. Oh yeah, big shoulder.
Strogatz: I mean, that’s a big punchline, isn’t it?
Shubin: Yeah, and it gets even better, because then we started to dig out the upper arm, the forearm, and even the wrist. You know, it had a neck. And yet it was a fish with scales, and you know, and it had a fish-like architecture to part of its skull. And it’s like we were just, like — that was a period of about eight months where these things were being revealed in 2005.
And you know, at the time there was a trial going on in Pennsylvania about intelligent design creationism being taught in schools, and people are arguing that there are no transitional fossils in the fossil record. You know, and here we designed an expedition to find one, and it’s emerging as we speak, a fish with arms and wrists and elbows…
Strogatz: Oh, crazy…
Shubin: And lungs, and all that stuff.
Strogatz: Wow. This story really hit me emotionally, not just intellectually. Because it just underscores how we’re part of all, like, this one big, long chain of being on earth. We’re part of one evolutionary family, you know? And it’s such an extraordinary adventure story, too. Think of the tremendous determination it took for Neil and his team to keep going back to the Arctic year after year, not knowing if they’re going to find anything.
And then, finally, they did. They found Tiktaalik. This is a, you know, the missing link they were looking for. They named it that because it’s sort of an homage to the indigenous people in the region where the fossil was found. “Tiktaalik” in Nunavut means a large freshwater fish.
Strogatz: Well, let me ask you a few more intimate questions. So when you’re up there having season after season, with maybe finding some things but not really, what you’re hunting for … were you married at this time or in a relationship?
Shubin: Yeah. Yeah. Oh yeah.
Strogatz: Like, do you have some kind of phone that you can call back home with?
Shubin: Yeah. So you have — and what happens is, it’s really hard sometimes. You know, relatives pass away. Right? I’m there for six weeks. You know, and initially, we have a cell phone, a sat phone. There’s no cell coverage. There is no wireless. But you know, we have a sat phone, so I’d call home every now and then. But yeah, things happen.
Strogatz: Did you have kids at home at that point?
Shubin: Adopting. Yeah, we were adopting.
Strogatz: So I mean, I’m just thinking, like, what it’s like for me when I go away on a trip, and then the question is, like, what got accomplished? And I’d say, well, this is the fourth time I’ve tried, and this was another dud. I mean, I’m exaggerating. I’m sure you were finding some stuff.
Shubin: No, you’re actually recounting the story of my life. [LAUGHTER]
Strogatz: Well, I’m wondering. That must be so hard.
Shubin: Yeah, it takes a village. Let’s put it that way. I remember one of the most challenging years was 2002. There was a lot going on for all of us at home. And I had come – gone to the Arctic and come back. It was our third season there. And I was asked — you know, it became known as “the fish” — “Did you find your fish?”
Strogatz: Yeah, did you find your fish?
Shubin: No, I didn’t.
Strogatz: “Oh, dad!”
Shubin: [LAUGHTER] And I didn’t. I mean, it’s like, no, when is this gonna end? [LAUGHTER] It was like – it was tough. It would actually be hard. But everybody, you know, you don’t do this without a ton of support.
Shubin: And so that’s what it takes because we’re not successful but for a small fraction of the time. Most the time I’m a total failure. [LAUGHTER] I’m learning from my failures. But, you know, it’s still their failures.
Strogatz: After the break, fish doctors, lazy bakers and salamander tongues.
[MUSIC PLAYING FOR BREAK]
Strogatz: I have a dog I love very much named Murray, who I was stroking. I mean, I like to pet him. He’s lying, he’s kind of tired. We had a good day of running around with his girlfriend out in the woods. And it just kind of freaked me out as I went from his shoulder to feel his, what would be his upper arm or his front, you know, that he has this big bone there. And then he’s got like an ulna and a radius in his forearm.
Shubin: Oh yeah.
Strogatz: And he’s got five toes. You know, I mean, I don’t have to tell you. But it’s just kind of an amazing thing that his arm is like my arm.
Shubin: Yeah. It’s one of the great examples from the biological world. That is, if you look at arms and legs of creatures that live on land, like us, you know? You have – what do you got? You’ve got one bone. You have the humerus. Right? You’ve got two bones. The radius and ulna. You’ve got little wrist bones. And then you’ve got the digits, the fingers. And the same thing applies to the hindlimb, you know, upper leg, mid leg, and ankle bones, and toes. One bone, two bones, little bones, fingers. And you see that. You see that in people. You see that in Murray the dog. You see that in salamanders. You see that in birds. You see it in whales that have returned to the sea.
Strogatz: That’s amazing.
Shubin: You see it in bats, that fly. It’s this beautifully, it’s this beautiful archetype, this underlying order to diversity of vertebrate appendages. And Darwin made a very specific prediction that — you know, biologists who were inspired by Darwin said, you know, “We should find versions of this in fish.”
Shubin: And if you look at the fin of Tiktaalik. It has fin rays. Right? Just like a fish fin, right? You remove that webbing, what do you see? You see one bone. Humerus. Two bones. Radius and ulna. You see a wrist bone or a few wrist bones, and you see things that can correspond to digits.
Strogatz: That’s what I wanted you to say. [LAUGHTER] Isn’t that incredible?
Shubin: You know, it never ceases to blow my mind. And it never ceases to blow my mind that’s knowable. Right? That we can use the tools of historical geology, of paleontology, to find those things, you know. And we can see how it was established over time, you know. And then other fish, if we look even more just in the fossil record, we see fish that have some but not all of that pattern.
So we can see this underlying order to the diversity, but we can also see how it was, you know, assembled over evolutionary time using the right tools. You know, and I remember when I was teaching, when I was — we found Tiktaalik, I was teaching human anatomy in the medical school at the time.
Strogatz: A human anatomy lab, we’re talking, like, cadavers?
Shubin: Medical students. Cadavers. Yeah. This is the first-year medical class.
Shubin: And these, you know, these future physicians were asking me, “What kind of doctor are you? Are you a cardiologist? Are you a nurse?” No. I’m a paleontologist that happens to work on fish. [LAUGHTER] They’re like, “What? Give me my money back.”
But it became clear that, like, knowing the evolutionary history is a very powerful way to teach human anatomy. So for me, you know, the limbs, the head, the basic structures and basic architecture of our body were originally established in, you know, fish living in aquatic ecosystems, you know, hundreds of millions of years ago.
And that’s knowable, deeply knowable from the fossils, from comparative anatomy, from all kinds of other disciplines including molecular biology, that it just became a joy to teach in terms of the human anatomy course in the medical school. So that’s why all these connections were so very important to me, and not only in my research, but also in, like, the ways that I communicate science.
Strogatz: That’s an interesting point there. Say a little bit more what you mean about that?
Shubin: You know, I was teaching medical students. And, you know, they’re like, “What is a fish paleontologist doing, you know, teaching human anatomy?” And that actually became a book. That became Your Inner Fish, which is my book.
Strogatz: Okay. [LAUGHTER]
Shubin: Because, you know, really connecting that — showing how, you know, inside of our bodies, inside of every organ, every tissue, every cell, you know, almost every part of DNA inside those cells is billions of years of history of life, artifacts of that history. You know, just like looking at the sky, that’s history. And it’s basically looking inside their body. So when you know how to look, our body is filled with history, artifacts at every level.
And I see it, and I live it, you know, as a paleontologist, but then bringing that story and the diverse fields that tell us that story, you know, became my first public effort in communicating science, and that was Your Inner Fish.
Strogatz: I mean, I feel a sympathy with what you’re saying. I don’t mean sad sympathy. I mean like you look at something and you see history. You see deep history. I look at something and I see math, you know.
Shubin: Well, that’s — you’re exactly right. It changes the way you see the world. And part of your joy as a mathematician, or in my case as a historical biologist/geologist, is in explaining that. And when you see some of the light go on in somebody, and then all of a sudden, they see the world like you do, it’s actually, really kind of fun.
Shubin: And that’s true for me when I look at a road cut in Pennsylvania or in New York. You know, I see ancient oceans. I see ancient rivers. When I look at the body, and you know how to look, I’ll see the history we share, you know, with dogs, and with salamanders, and with fish and so forth, and our limbs and elsewhere. You know, it changes how we see the world, and there’s a joy in that.
Strogatz: One of the things that makes Neil’s work so interesting to me is that he looks at biology from so many different perspectives. On the one hand, he’s thinking about history and geology. On the other hand, he’s thinking about molecular biology and development and genes. And, you know, that’s partly why Neil doesn’t totally agree with the popular idea in evolutionary biology that goes by the name of contingency. Contingency is the idea that accidents and randomness dominate the story of evolution.
Like think of the asteroid that just happened to hit the earth 65 million years ago and wiped out the dinosaurs and made room for mammals. Or think about the weird backwards anatomy of the human eye, where our nerves enter our retinas from the front and cause a blind spot and get in the way. That seems like some kind of weird evolutionary accident. That’s not the way you would have designed anything. We’re just stuck with it. But Neil is pushing against this idea of contingency as a dominant force because he sees a lot of logic in evolution.
Shubin: You know, if you think about organisms, they have common genes.
Shubin: They have common developmental processes, you know. If they have similar sorts of initial conditions and boundary conditions, the outputs might be very similar in different cases.
Shubin: As you might have — the independent evolution of similar states may be more regular then you’d predict if you subscribe to a completely contingent view of evolutionary change.
And, indeed, if you think, if you look at the evolutionary record, it’s just loaded with multiples, loaded with cases, where you know similar inventions have happened independently. And for a long time, people thought these were confounding factors that they, you know, they just get in the way of our ability to reconstruct the patterns of the history of life. But, you know, the more we look, the more we realize that that mess is really the message. That similar outcomes can happen, arise independently, you know, just given the basic biology of creatures.
And you know, it’s not unusual that, you know, every creature that flies has some sort of wing. Right? [LAUGHTER] But it gets less trivial, right. It starts getting downright wacky. [LAUGHTER] So it’s like one of the examples I use in my book, I look at salamander tongues, which is this incredible invention, and it was one of my mentors, David Wake at Berkeley, who has been working on salamanders and their tongues for years.
Shubin: But it sounds strange, right?
Strogatz: [LAUGHTER] It’s a little strange. I mean salamanders would be good enough. But, no, not that. “I’m going to specialize in the salamander tongue.”
Shubin: Yeah, they — but then when you sit with him, your mind gets blown, just like with any scientist at the top of their game working on whatever system. So there are two kinds of animals in the world. Right? There are animals that bring their mouth to the prey. Think lions. And there are animals that bring the prey to mouth.
Strogatz: Like salamanders.
Shubin: They flip out their tongue and bring it back. So salamanders have this amazingly specialized tongue, and it’s ballistic. They kick it out with a variety of specialized structures. What they do is they shoot a series of gill bones wrapped in connective tissue tethered to a tongue, it shoots out half a body length in seven milliseconds. Hits an insect. And then it, the whole thing, just as fast, comes back in the mouth.
Strogatz: I’m picturing, it’s almost like a pop gun or something that’s got a cork or something.
Shubin: Yeah. That’s right.
Strogatz: Is that right? You tell me. What’s the right metaphor?
Shubin: Yeah. So this basically is something hard that you tethered to an elastic connective tissue that kicks out. It’s, you know, half a body length in seven milliseconds, and then comes back after attaching to the insect.
Strogatz: Is it a sticky thing, or it a grabby thing?
Shubin: Yeah, it’s a sticky pad. It has a sticky pad at the end. And that sticky pad just brings the — it attaches to the insect. And then the insect is attached to it, and then it’s reeled into the mouth.
Shubin: And it involves very specialized structures. Those are gill bones that are modified. It’s basically shooting out faster than the contraction of the muscles could do. So, basically, it’s a system that’s functioning like a slingshot almost. And it involves, you know, countless changes to the head, to the muscles, to the body, and behavioral changes, neurobiological changes as well. So that’s, I mean, when you think about that, it’s an amazing biological machine.
But what’s even more amazing about it is when Wake looked at the evolutionary history of salamanders, he found that amazingly complicated biological machine evolved at least four times independently. [LAUGHTER] Okay. Nothing contingent about that.
Strogatz: No, exactly.
Shubin: And then that — I mean, it’s the same mechanism. And each of those salamanders that did it had some properties that were similar. Number one, they had similar patterns of embryological development. Number two, they had lungs. They didn’t use the gills to breathe in adult stages, and they also didn’t have larval stages.
Strogatz: Wait, so they’re — you say they did not use their lungs to breathe?
Shubin: They had lungs to breathe. They didn’t use their gills to breathe. So they had lungs.
Strogatz: Oh, I see. They have lungs.
Shubin: Yeah. Mm-hmm. So in this case, you had certain preconditions. When those preconditions were met, those groups of salamanders evolved, tended to evolve this amazing biological machine independently, you know. And so we see that again and again and again. We see, you know, the independent evolution is similar, body plans in different animals. We see the independent evolution of similar types of limbs in different creatures. Again, it’s basically … there are sort of biases. There are certain outcomes that are more likely than others, and we see them happening repeatedly.
Strogatz: Apparently, some of the same structures can evolve over and over independently because the dice are loaded, you could say it that way. You know, evolution is sometimes playing with random dice that are actually loaded dice. They favor certain outcomes, and so you see certain things popping up again and again.
Strogatz: There’s a story about 2,000 salamander feet where you showed a kind of bias.
Shubin: [LAUGHTER] That’s right. I had finished at Harvard, and then I went to Berkeley to enjoy the California sun. But like within about three months of me arriving in Berkeley, it was hit with the coldest freeze snap it had in years. And so what I did is — it got really cold up in Point Reyes National Seashore, which is in Marin County just north of Berkeley, the Bay Area. And some of these ponds, ephemeral ponds, froze and in so doing left the carcasses of thousands upon thousands of salamanders.
So I was in David Wake’s office. He’s the gentleman I was telling you about with the salamander tongues, and he was on the phone with somebody from the National Park Service saying, “Hey, we’ve got thousands of salamanders that were killed in this freak freeze. Where do you want them? Where do you want ’em?” And he looks like, “You can use those thousands of salamanders?” I said, “Yeah, we’ve got — let’s look at variation. Let’s look at the variation of hands and feet to find out if there are common rules to how they vary.”
So we got the salamanders, and we spent about a year — no, close to a year and a half, two years, preparing them in such a way that we could see inside their limbs. We’d clear and stain them. So what you can do is take the body and you can treat it with chemicals, so that at the end result, after a couple weeks to a month, you could — the body becomes clear and the bone stain red and blue.
Strogatz: Oh, wow.
Shubin: It’s really amazing. It’s true. These are like works of art.
Shubin: Anyway, we did that with all these things, and we could see all their limbs and we could see their little, tiny bones that make up their wrists and ankles. There are about nine or 10 of them. And we mapped those bones out. And we found when we mapped them out, that certain kinds of variation were much more common than others. Certain bones would fuse together, where you would have two or three bones primitively. In some variants, you’d have just one big one, where it was clearly fused. In others, bones would split apart in different ways.
And so we made a catalog of all that variation, and we found, wow, the variation we see in these populations of thousands of salamanders, it’s not random at all. Certain variants are way more common than others. Okay. That’s kinda interesting, but nothing revolutionary there. But then we started to look at salamander history, the evolutionary history of salamanders, and it turns out that the patterns of variation we saw in that population that were most common were the most common patterns that you’d see in the evolution of other groups of salamanders.
And furthermore, those patterns were ones that would appear independently again and again in different kinds of salamanders. So it seemed to be there was a signal that we’re seeing. That, number one, the evolutionary history of salamanders was riddled with multiples, that is the independent evolution of not only similar kinds of projectile tongues, but also the patterns of limb bones. And that we’re seeing insights in that to the way that the variation within the populations of salamanders were biased, themselves.
So it’s a long way of saying that what we were seeing is a window into why the evolution of salamander hands and feet was riddled with multiples, was not contingent because the patterns of variation that existed within the species was themselves constrained. It’s almost like if you have a recipe with certain ingredients and certain processes, it’s going to bias the outcomes of the kinds of cupcakes or things you can produce.
Shubin: Right? In this case, it’s bodies. [LAUGHTER] And the recipe and the ingredients, the ingredients in this case are the proteins and genes. The recipe is how those genes interact and how those cells interact. Let’s go with that a little bit.
Strogatz: Let’s move into the kitchen because you have an analogy in this new book Some Assembly Required that I really liked where you said: “Mother Nature is a lazy baker.” [LAUGHTER]
Shubin: Yeah. One thing we’ve learned is that there are common biological processes that underlie everything from fruit flies to people, and that those biological recipes, similar genes doing similar kinds of things, similar embryological processes and development — that they make organs as different as, you know, fly legs and human arms. Those are really remarkable in the way that they can power new kinds of research, and what they’re telling us about evolution.
So for instance, one of the big turning points of my career was sort of a revolution that happened in the 1980s where people were beginning to uncover some of the genes that build bodies. And they were finding that some of the genes that control the body architecture — which organs are in which part of a fly’s body — they’re beginning to understand them, but it turns out that they were finding those same genes in mice and people doing similar kinds of things.
Shubin: I remember seeing those papers and thinking, “Oh my goodness. I need a new toolkit.” [LAUGHTER] I was trying to be a paleontologist, now I got to shift over and do a little more molecular biology and development, which is eventually what I ended up doing much more of.
You know, what we’re seeing through several decades now of molecular biology is sort of commonalities, connections of the toolkits that build bodies as different as flies, worms, fish, and people. Each of those critters has parts of the toolkit that build our own bodies, that the insights of the basic biology from flies and worms are really giving us deep insights into our biology. And the only reason that is true is because of evolution, right, because we share an evolutionary past.
And that nature has been this lazy baker, that is these mechanisms for building bodies, and organs, and so forth, exist as modules that are redeployed over and over again, and modified. So it’s very powerful window into how we approach science now, but it also tells us something powerfully about evolution, right? That we’re seeing antecedents of structures that are way more ancient and different than we could have ever expected because similar kinds of genes exist in people and flies.
Strogatz: So I mean another thing that that occurs to me is, more broadly, evolution can refer to all kinds of things besides living things. Like languages evolve, cultures evolve. Inventions.
Shubin: Oh yeah. Technology.
Strogatz: Technology. Exactly. So I’m wondering if you have some thoughts for us about that, what we can learn about the nature of invention and innovation generally.
Shubin: One thing I was impressed with when I was thinking about the new book, and I was thinking about the story of multiples — independent origins of different body plans, origins in the evolutionary record — I started to look at the record from the business world, technological world, in terms of inventions. And, of course, the world of multiples is really profound in the technological world.
Think of an invention that’s been invented, it came about — any particular invention likely came about multiple times independently at the same time with different inventors. Just like evolution does. So there’s, you know, something in the air that fosters technological inventions. The same thing is true in biology. There’s something in the air. It’s understanding the mechanisms in biology that bring about the current conditions.
Strogatz: So what should what we remember from the recent past? Like VHS and beta were two different — are they multiples in this sense?
Shubin: Yeah, the telephone, Alexander Graham Bell. There’s somebody else who came up with the telephone at the same time. You know, you can look at almost any particular invention, it had multiple inventors. It was probably invented multiple times independently, at least in general form, and tracing the antecedents of it, of inventions, becomes, you know, an incredibly challenging task. That’s why, you know, patent lawyers are — their whole discipline. If was easy, they wouldn’t have jobs. But it’s really hard and it’s really challenging, and that’s the exact same thing we see in evolutionary history.
There’s a couple of patterns. Number one is the invention that’s associated with the biological revolution is almost never associated with that biological evolution [LAUGHTER] evolutionary.
Think about lungs, right? Fish — creatures that walk on land have lungs, and lungs are an invention to live on land. Feathers are an invention to fly. Right? All those things. If you think about them, they’re so obvious that they’re logical and true. But the reality is as we trace those inventions, what we discover is those simple stories are never true.
Lungs originally arose in fish living in water. Feathers arose in dinosaur creatures that needed thermal regulation, sexual signals, and so forth. So inventions, one of the biggest things behind the origin of inventions, is not just the structure of the invention itself, but the way it’s used and the way it’s deployed. And that’s true with technology as well. The difference is, though, it kind of depends on how information is transferred from entity-to-entity.
So, biologically, we have two ways of transferring information. From generation-to-generation, so called vertical, you know, from parent to offspring. And that’s the classic Darwinian evolution. Right?
Shubin: But then there’s the other kind of evolution that happens like, you know, you share an idea, a mathematical idea with me, and then I share with 10 other people. And they share with 50 other people, and that spreads really fast. Right? So it’s cultural practices and so forth. That’s horizontal transformation — transfer of information. We’ve seen in the distant past, about 10% of our genome is composed of defunct viruses that have been put to use in different ways or been rendered extinct.
But the process of invention, which consists of origins and disruptive inventions, which changed the world, is itself really complicated because the, you know, the search for antecedents of inventions always takes us to places that are truly surprising, that we would never expect. And I think the same thing is true for biological inventions as it is for technological inventions.
Strogatz: Well, I mean, so a classic one is the printing press, which grew out of something that used to be for pressing wine for grapes.
Shubin: There are other cases, too, like sticky notes and soft glues.
Strogatz: But what was it about sticky tape again? The idea was?
Shubin: The sticky. So they basically had the soft glues. And so somebody at 3M decided that, you know, that they have these glues that were not like really super strong, And the idea was, well, why would you want to glue this? It’s not super strong. So somebody kind of figured out, well, if I just take this like sort of soft glue and put it on the back of a piece of paper, I can like, you know, make little notes to myself. So sometimes great inventions or great moments in evolution, we only know post hoc, right? We only know them looking backwards.
So if you and I were to take a time machine, and we would go back about 375 million years ago. First of all, we’d need air tanks to breathe. There wouldn’t be enough oxygen for us, but that’s beside the point. But anyway, so we get down there, and we’re looking in these like ancient Devonian rivers and streams, and we’re looking at all the fish in there. I don’t know if you or me could predict the true revolutionary.
If we saw Tiktaalik in that stream, would we be able to say without knowing what Tiktaalik’s descendants and cousins did, that it was a revolutionary, that it was going to lead to a whole gig? No, you’d see a fish with a flat head, with a crazy fin that was flapping around in the mud. You’d probably think it was kinda lame, you know. [LAUGHTER]
Strogatz: [LAUGHTER] So the thing that later became our arms was, at the time, a kind of lame fin, you’re saying?
Shubin: It was walking in the bottom of the water, walking in mud flats. It was a fin, but it wasn’t the best fin. It was a good fin for supporting the body. But you wouldn’t know at the time. We’d only know after seeing its descendants that it was so successful. Right? And so, you know, a lot of these great inventions and great transformations, we only know by looking backwards.
Strogatz: You summarize it very well with a quote in the book that I had never heard before. Something like, “Nothing ever begins when you think it does.”
Shubin: Yeah. So I was writing this book, and I was just doing some reading outside of biology. And I was reading about Lillian Hellman. She had quite the life, quite the human being. Anyway, I was reading it, and there was a quote that she said. It says: “Nothing, of course, begins at the time you think it did.”
Shubin: And it was from her. She was talking about her own life. I was thinking, well, that’s biology in a nutshell. [LAUGHTER] That’s the story I want to tell. That’s kind of what I work on as a paleontologist. It’s always deeply surprising. And, again, the texture of those surprises is what informs us about fundamental mechanisms of biology. You know, how these things arose. How the genes changed, or the developmental processes changed.
Strogatz: Is there something you can tell us about what you’re thinking about now? Are you still trying to think about transitions or —
Shubin: Yeah, very much. So a couple things. One of the big things we’re thinking about in the laboratory right now is, if you look at our arms, if I was to get my hand cut off, it wouldn’t grow back. Yet, if you look at salamanders — we’re getting back to salamanders, and this is not their tongue — if you cut off a salamander’s arm, the entire thing grows back.
Shubin: Bones. Muscles. Nerves. Blood vessels. And it turns out salamanders are not unusual, that other critters do it as well. Lung fish … fish generally. So it seems to be that it’s not like salamanders evolved this amazing regenerative ability. It’s our lineage that has lost it. So what we wanna do is use evolutionary principles to understand regeneration.
Strogatz: When Neil probes the mysteries of how salamanders can regenerate their limbs, I see him as a scientist riding across a lot of different swaths of biology, all kinds of different scales. You know, from the smallest scale, like genes and molecules, up to the next level of organ systems, and then whole organisms, and finally up to the level of entire populations or communities. You know, we often have different names for the biologists who study these different scales, but Neil is doing all of it. He is a biologist in the broadest sense. He thinks about all of life at every different level, and I think it’s a really beautiful and thrilling picture to look at life that way as this one big, unified story.
Next time on The Joy of x, biologist Bonnie Bassler on her cutting-edge discoveries about the communal life of bacteria.
Bonnie Bassler: So you’re a huge host. If a couple bacteria get in me and they dribble out a couple of these poisons or toxins, nothing is going to happen. But if they wait and they count themselves, and they recognize that if all of us secrete these poisons together, like an army, then these exoproducts, these proteins, will have consequences to the host, right, and they might be able to overwhelm your immune system.
Strogatz: The Joy of x is a podcast project of Quanta Magazine. We’re produced by Story Mechanics. Our producers are Dana Bialek and Camille Petersen. Our music is composed by Yuri Weber and Charles Michelet. Ellen Horne is our executive producer. From Quanta Magazine, our editorial advisors are Thomas Lin and John Rennie. Our sound engineers are Charles Michelet, and at the Cornell University Broadcast Studio, Glen Palmer and Bertrand Odom-Reed, though I know him as Bert. I’m Steve Strogatz. Thanks for listening.
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