MR. KOJO NNAMDIWe all remember the drawings from high school text books, strange-looking fish that emerge from the water and eventually walk across land. But when exactly did fins develop enough to make that possible? And would you believe that those same fins eventually evolved over hundreds of millions of years into the arms and hands we humans have today? Paleontologist and evolutionary biologist Neil Shubin spends his time looking for answers and probing the puzzles of human evolution.

MR. KOJO NNAMDIWhy do our bodies look the way they do? And what's our place in the natural world? His research takes him to ancient rock beds in the Artic and requires many years of careful digging to uncover fish fossils that help explain human evolution. His work is featured in a new PBS program that airs next month. It's called, "Your Inner Fish." And Neil Shubin joins me today.

MR. KOJO NNAMDIHe's a paleontologist and a professor and associate dean of biological sciences at the University of Chicago. He's author of "Your Inner Fish: A Journey Into the 3.5 Billion Year History of the Human Body." He's also the author of "The Universe Within: The Deep History of the Human Body." Neil Shubin, thank you so much for joining us.

DR. NEIL SHUBINThanks for having me on.

NNAMDII know our listeners want to join this conversation, so let me tell them how. It's 800-433-8850. What questions do you have about how the human body evolved? You can also shoot us an email to kojo@wamu.org. Neil Shubin, how did you get interested in fish paleontology and evolutionary biology?

SHUBINIt was an interesting path. I was teaching human anatomy to medical students at the University of Chicago. You know, this is the course where students see the human body and dissect it for the first time on the human cadaver. And I was always interested in paleontology. And I was always interested in fish paleontology.

SHUBINBut what struck me was the students would approach me in the class in the early days and they'd say, you know, "Hey, Dr. Shubin, what kind of doctor are you?" You know, "Are you a cardiologist? Are you a neurosurgeon?"

NNAMDISure.

SHUBINI said, "Well, no. I'm a fish paleontologist." And they'd be like, what? I'm going to need my money back on this. But, you know, but it becomes very clear that if you want to understand the human body, the best road maps lie in other animals. And often those best road maps are fish. And I was very fortunate to have spent much of my career finding such fish that tell us about our bodies.

NNAMDIHow do embryos demonstrate that the human body carries the legacy of creatures that lived millions of years ago?

SHUBINWhat is so powerful here is that we can trace the development of our body structures from egg to adult. We can look at the cells and how they behave. We can look at the jeans and they direct the behavior of those cells. And we're beginning to unravel that process. What's amazing is we can begin to look to fish and other creatures and ask, do they have those processes as well, too?

SHUBINHow do fish build their fins, genetically and developmentally? How do people build their limbs, genetically and developmentally? And the answer lies -- they use versions of the same genes and versions of the same developmental processes to make fins and limbs.

NNAMDIOne of your big projects featured in the upcoming PBS program was to find the point at which fish emerge from the water to live on land about 375 million years ago. Your research involved traveling thousands of miles to the Canadian Artic and being plopped down by helicopter in a barren landscape. How the heck did you know where to go?

SHUBINYeah, exactly.

NNAMDIAnd what were you looking for?

SHUBINRight. Well, you know, the funny thing about that was it was totally planned. So what we did is my colleagues and I -- Ted Daeschler's in Philadelphia and I -- sat down and thought, okay, where are the right rocks of the right age preserved in the world where we can work them at the surface. And it turned out one of the best and unexplored places was up in the Canadian Artic, about 800 miles from the North Pole. These were rocks of 375 million-year age.

NNAMDIWhat makes the Artic such a good place?

SHUBINWell, those rocks are exposed to the surface. It's a desert. That's what most people don't realize. It doesn't get a whole ton of snow. So those rocks are exposed to the surface. They're relatively unstudied by paleontologists. So they're still a lot of basic exploration to be done. And so that appealed to Ted and I. So off we went, honing in on the right kinds of rocks. It took us six years, but one day in 2004…

NNAMDIBut wait, if they're well exposed to the surface, can they also be well preserved?

SHUBINYeah, that's what the amazing thing is. So what we paleontologists do is -- we hate to dig. And it's not just because we're lazy, although that's probably part of it, but what we look for are bones at the surface. So we spend a lot of our time walking over the landscape of the right rocks, to see bones that are eroding or weathering out. What's beautiful about the Artic is you have this freeze/thaw. It's really, really cold in the winter, less really, really cold in the summer.

NNAMDIYes. For about six weeks, right?

SHUBINAnd, you know, so -- right, exactly. And so the rocks expand and contract. And what they do is they begin to break up. Often if there are fossils inside, the fossils are harder than the rock and they'll move to the surface. So we spend a lot of our time looking at the surface. We found one such place, dug in. It took us a couple years. And boom, we found it.

NNAMDIWe're talking with Neil Shubin. He's a paleontologist and professor and associate dean of biological sciences at the University of Chicago. He's the author of "Your Inner Fish: A Journey into the 3.5 Billion Year History of the Human Body." Today, we're talking with him also about the new PBS program that airs next month called, "Your Inner Fish." If you'd like to join the conversation, give us a call, 800-433-8850. What anatomical quirks do you think date back millions of years? 800-433-8850. You can send email to kojo@wamu.org.

NNAMDIOr you can go to our website, kojoshow.org, as a question or make a comment there. Neil Shubin, can you explain what the fossilized Tiktaalik fish you found tells us about the origin of, well, my hand?

SHUBINYeah, exactly. So, you know, here's a fossil. If I was to show it to you it would be about four feet long. It would have scales on its back, just like a good old fish. It would have fins, with fin webbing, fin rays, just like any old fish. So at one level you'd say it's a fish. But then you'd look at its head. It has a flat head with eyes on top. Very -- almost crocodile-like in a way. Then if you looked inside those fins, take the scales out, take the fin webbing off, it has an upper arm bone, and elbow, a forearm, even parts of a wrist, inside the fin.

SHUBINIt has both lungs and gills. It had a neck. No fish has a neck. Its head can move independently of its body. So what we can do is see early versions of parts of our own body in these fish and its evolutionary cousins. And it's not just this one fish. There are number of them now known. And we can begin to trace the fossil record from this fish to early amphibians through things we can, you know, like reptile-like creatures and then mammals.

SHUBINAnd so we can follow the elbow. We can follow the wrist. We can follow the neck from fish to us. It's not just one line of evidence, it's many. And when you do that you're left with the realization that, you know, every time you bend your wrist, every time you move your head, you can thank Tiktaalik and its evolutionary cousins for adapting in life in water 375 million years ago for parts of our own bodies.

NNAMDII'll never look at my wrist the same way again. But this is a painstaking process. It took six years of looking and only two of them in the right place before you found the fossil you wanted. How does one muster that kind of patience, that kind of perseverance and how do you learn from the failures you experience along the way?

SHUBINThat is a fabulous question because so much of science is learning from your failures. Most of our experiments don't work. Most of our field work doesn't work. So what we had to do for the first few years is to learn the right geology. And the only way we could do that was by seeing those rocks, evaluating those rocks, looking for bones in it. Then we found the layer. We had to train our eyes to find those fossils. It's not easy because the fossils are the same color as the rock.

SHUBINTurns out we were walking on some of these for several years before we found Tiktaalik, but, you know, that's just between you and me. But, you know, we had to train ourselves that way. And ultimately we had to learn the fossilization conditions that are unique to that Artic site. And, you know, over time you get better at it. And we believed in this project.

SHUBINWhat kept us going was each year we found just enough to get us back. We had funders who believed in us, who hung with us through thick and thin. And you put all those things together with a field crew that works very well together, and it all came together.

NNAMDIThe part I like is the three of you guys on your hands and knees essentially crawling one behind the other, and then one person says, hey, what do you think I have here?

SHUBINExactly. It's teamwork.

NNAMDIVoila

SHUBINYeah, exactly.

NNAMDIA flat-head fish.

SHUBINBingo. It's real teamwork in that way, you know. And that's why it pays when you're in the field to have a group that have very complimentary expertise.

NNAMDIHere is Adam, in Bethesda, Md. Adam, you're on the air. Go ahead, please.

ADAMOh, hi. Thanks for taking my call. I'm sure it's going to be a great show. I just wanted to tell the doctor, you know, he reminds me of one of my favorite parts of Richard Dawkins's book, "The Ancestor's Tale." Is when he -- I think he gets into the aquatic parts. You know, it sort of traces the story of human evolution backward through all the different intersections through time. But when he gets to like, I think, the aquatic section, where we meet up with our, you know, our aquatic ancestry parts, that we are basically -- the human body is basically donut-shaped.

ADAMAnd it's just -- that path, you know, based around, you know, our alimentary canal or whatever, that just fundamentally changed the way I looked at the human body's construction. I'm feel at the sort of part of where you look at, too.

SHUBINYeah, that's a brilliant way to look at it. If you take -- let me just explain that because I think what you on is a wonderful point. That is if you take a cross section of the human body, you know, like through the waste, you know, or through the midsection, just cut us in half, if you will (unintelligible) for the gory thought. But essentially we're a tube within a tube. There's an outer tube, which is the body wall and the muscles and so forth.

SHUBINAnd then there's an inner tube which is our gut tube. That tube within a tube construction forms in us very early on. And there are a number of genes that are responsible for patterning those tubes. Turns out if you look at other embryos, fish and other creatures, even worms -- some worms -- now you're talking about your inner worm, they also have this sort of tube within a tube construction. And oftentimes many of the genes involved in patterning those, you know, set of tubes, front to back, top to bottom, and so forth, are similar versions of the same ones.

SHUBINSo that is what I'm saying, you know. When you start to see these deep similarities, you start to see our connection to other animals. And what's important here -- and you brought it up with your question -- is we see many layers of history inside of us. You know, I'm here talking about inner fish. Your question just brought up, you know, you hear inner worm, if you will…

NNAMDIYeah.

SHUBIN… (unintelligible) for lack of a better word, but, you know, you see these different layers embedded in us. And seeing our history is like, you know, peeling layers of onion, you know, layers of an onion. You know, you peel that first outer layer and you see the history we share with primates or the primates. Peel the deeper, you see the history we share with mammals, then reptiles and amphibian-like creatures and fish and worms and, you know, yeast and microbes and everything like that. So, yeah, thank you.

NNAMDIAdam, turns out…

ADAMYeah, I -- oh, I'm sorry.

NNAMDIGo right ahead, Adam.

ADAMI teach at American University. And my students are about to start reading "Origin of the Species," read the whole thing. You know, and like the second to last chapter is -- basically he says, you know, if I only had morphology and embryology, that would enough to convince me. He spent like 400 pages laying out all this other great evidence, and it comes down to it could just be this. That would be enough. It's so convincing.

SHUBINYou know what's amazing about that is when Darwin wrote the "Origin of Species," he didn’t know any genetics. He didn't know molecular biology.

ADAMRight, right. It's amazing.

SHUBINNone of that stuff was invented yet. And that stuff is just utterly convincing. You know, with each new…

ADAMYes.

SHUBIN…genome project, you know, each new sequence, which thousands are happening each day, you know, that's yet more evidence of which Darwin could never have anticipated, you know, working, you know, over a century and a half ago.

NNAMDIAdam, thank you so much for your call. We move on now to Joe, in Alexandria, Va. Joe, you're on the air. Go ahead, please.

JOEYes. Hi there. Yeah, you just mentioned Darwin, and that was part of my question, the age old question, if we have somehow evolved from something and, in this case the discussion of fish, why is that that something still continues to exist and evolve? Where is the branch…

SHUBINWell, right.

JO…point where, you know, we kind of broke off, sort to speak, that continued on and we continued on?

SHUBINYeah, that's a good going point. So the -- that's a question you get a lot. And I think that illustrates a very important point. We're all relatives. Okay. So fish our cousins and they're our distant ancestors. So when, you know, I was born all my relatives didn't die. You know, all my cousins are still around. So, you know, so think about the evolutionary tree as a tree of cousin-ness. And, you know, we have close cousins and cousins farther away.

SHUBINYou know, fish are one set of cousins, you know, worms are even further away. So we have, you know, this -- each branch of the tree of life flourishes in its own way. So when one species is born -- comes about, other species don't necessarily go extinct. Just as, you know, when I was born, all my first cousins didn't die, fortunately.

JOERight, right, right.

NNAMDIJoe, thank you very much for your call.

JOOkay. Thank you.

NNAMDIYou, too, can call us at 800-433-8850. Would you describe yourself as more fish, reptile or monkey? 800-433-8850. Our guest is Neil Shubin. He's a paleontologist and professor and associate dean of biological sciences at the University of Chicago. One episode in the PBS program that we're talking about, focuses on your inner reptile. What did reptiles contribute to the human body? And where did you go in search for clues about that?

SHUBINWhat was really fun about filming this series is we went from Africa to the Artic to southern Canada to the American West. It's truly a global show. And one of the great stopping points is, as you say, the reptile piece. Because if you follow the sequence of fossils that show the transformation from a reptile-like creature to a mammal, what you can begin to do is trace the history of some important parts of our bodies.

SHUBINSurprisingly, what you do is when you see a reptile jaw, you know, that holds the teeth, the jaw is composed of many bones. Our jaw's only composed of a single one, right. How did that happen? Well, what happened is you can follow the history of that reptile jaw with many bones, and what you see is over time some of those bones at the back of the jaw get smaller and smaller and smaller over millions of years, smaller and smaller, until eventually they become bones in our middle ear.

SHUBINWhat's inescapable when you follow that series is that the bones that exist in our middle ear, which help us hear so many different kinds of sounds, originally came about as portions of the jaw bone of reptiles. And what's important about this example, it's not just based on that beautiful fossil record, it's also based on the embryos and DNA. Because if we follow the development of those bones, they originally form in us as part of the series that connects to the first gill arch, which includes the jaw bone. So it's a wonderful story actually.

NNAMDIThat beard, up here, it's my understanding that our hair is linked to the -- I say this because Neil Shubin has a beard, for those of you who can't see him. Our hair is linked to the whiskers of reptile-like mammals?

SHUBINWell, yes, very much so. So the first source evidence of hair that we see in the fossil record is as sensory organs of the creatures. These vibrissae, if you want to call them that -- that perceive sensations from the outside world. And what's important to understand about hair is it's one of a class of organs that form inside skin. And there are many different kinds of organs that form inside skin, from different kinds of glands to certain types of scales.

SHUBINAnd each of these shares certain commonalities, certain recipes of development, if you will, from genes and processes. And the kind of genetic and development recipe that builds a hair, is a version of the same kind of genetic recipe that -- different, but modified -- that builds a feather, that builds a scale, that builds a sweat gland, that builds, you know, various types of other glands in the body.

NNAMDII can see those medical students saying, right now, okay. They can keep our money for the time being because this is all of a sudden beginning to make sense to us. Here's a Mamardu (sp?) , in Washington, D.C. Mamardu, you're on the air. Go ahead, please.

MAMARDUYeah, Kojo, good morning to you and your guest. A previous caller just mentioned, I mean asked a question. And…

NNAMDIWhy does the species continue when it has evolved into something else?

MAMARDUExactly. And your guest response was that when he was born and all his cousins didn't die. But his cousins are still human, you know. So when I go back to his explanation, we came from different species, right? Let's say the fish, right?

NNAMDIYes.

MAMARDUSo we became human, but the fish be like the other fish. So how did that come about? Because when I try to understand the explanation of evolution, it's one species that goes from one state to a new state, a different state. Right? So when that happens, that new states keeps on living on, like as human, but the fish still remain the fish.

SHUBINThat's correct. So what you're seeing -- so what you're thinking is a notion of evolution is a continual progress. One thing transforms into the next, transforms into the next. What we see in evolution, in the genetic record, as well as the developmental record and the anatomical record, and when we layer in the ecology and how creatures live, is it's not that at all. It's a tree of life. So fish are still very successful in their aquatic environment.

SHUBINIt's not like, you know, there's this inexorable progress from one thing to another that, you know, creatures invade land and then because of what they've done all fish go extinct. You know, fish still can make a very good living. It just so happens that creatures that have invaded land have found a whole new strategy for success. So there are multiple pathways of evolution. And then we see that in the fossil record and we see that in ecology.

NNAMDIThank you very much for your call, Mamardu. We got an email from Ross, who writes, "I did evolutionary genetics research in college. Why do you not give more attention to homeoboxes in "Your Inner Fish" book? How important are homeoboxes? And because homeoboxes are so stable through time and resistant to mutation, how do they factor in when we evaluate the process of natural selection acting on gene variability?"

SHUBINGreat question. One of the whole chapters in my book is based -- is on homeobox, their discovery and their activity. In fact, that's one active area of research of my own lab. What's interesting about homeobox genes -- and they're so important in evolution -- is that we don't find a ton of changes in the homeobox itself, that portion of the gene. These are genes that assist in the development of the basic architecture of fly bodies and human bodies.

SHUBINThe reason why this caller brought this up is here's a genetic toolkit, that was first identified in flies, showing, you know, where certain kinds of organs are positioned in the body of flies. Turns out humans have versions of those homeobox genes, as well as do fish and other creatures, functioning in analogous ways, very similar ways. What's interesting here is the more we studied homeobox genes, what we find is that much of the change in them is not of the genes themselves, but of the control sequences that control when and where those genes active.

SHUBINSo while the genes themselves might have some change, but not a lot, where we see most of the change is in the switches that control the activity of the genes. So you're not necessarily inventing a new kind of gene per se, although that happens a lot. In this case, what we're seeing is lots of evolution by changing when and where those genes are active. And indeed that's a very hot area of research right now.

NNAMDIGotta take a short break, when we come back, we'll continue our conversation with Neil Shubin, he's a paleontologist and professor and associate dean of biological sciences at the University of Chicago and author of "Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body." We're also talking about a new PBS program that airs next month. It's actually called "Your Inner Fish," and that's where Neil Shubin's work is featured. If you'd like to join the conversation, give us a call, 800-433-8850. I'm Kojo Nnamdi.

NNAMDIWelcome back. Our guest is Neil Shubin. He is the author of "The Universe Within: The Deep History of The Human Body," and he's also the author of "Your Inner Fish: A Journey Into the 3.5 Billion Year History of the Human Body." His work is being featured in a new PBS program that airs next month. It is called "Your Inner Fish." Neil Shubin is a paleontologist and professor and Associate Dean of Biological Sciences at the University of Chicago. Neil Shubin, you have even traced some of our physical quirks, like hiccups, to our evolution from fish. How are hiccups a vestige of the transition from breathing with gills to breathing with lungs?

SHUBINYeah, so when you study our history, what you start to see is sometimes, when our bodies go wrong, when quirky things go bad, that's related, in part, to our history. The -- a hiccup, think about what a hiccup is. You know, we all have them. What is it? It's that, right?

NNAMDIPlease don't start.

SHUBINWhat causes that hic is a sharp inspiration, right? You're breathing in real quickly with a closure of a flap of tissue at the base of the throat called the glottis. And to have that happen involves a very stereotyped, standardized pattern of activity, of nerves and muscles that begins in part of the brain stem. And it's a very rigid sequence. Inspiration, closure of the glottis, hick. OK? And that goes again and again and again, and it can last, sometimes, for a very long time.

NNAMDIToo long.

SHUBINYeah. I'm afraid so. But, you know, we can begin to look to see, in the animal kingdom, what other creatures do this? And when you begin to see that, you find that a hiccup is a very common thing. And, in fact, it's a normal way of breathing for certain kinds of creatures that have both gills and lungs. So, if you look at tadpoles. As they develop, they have both gills and lungs. Like a frog tadpole, right? And there's a stage where they have both. Well, when they are breathing in the water, bringing the water into their mouth, they don't want it to go in their lungs.

SHUBINSo, what they do is they do a sharp inspiration. They close a flap of tissue at the base of the throat, called the glottis, and it stops that water from going into the lungs and shunts it across the gills. So tadpoles, for a particular stage of their life, breathe with a form of a hiccup, which involves the same stereotyped pattern of nerve and muscle activity that we see that's stimulated in us. So, this sits deep in our brain. It's a remnant of our past. We probably use that circuit in some way, in some unknown way right now, which we don't know about. But, it's probably involved in some way in some other activity, which is still a bit of a mystery.

NNAMDIOn to the telephones again. We'll start, this time, with Robin in Rockville, Maryland. Robin, your turn.

ROBINThank you. I had a quick comment on a question for your guest. Very interesting program. When I was in high school, I actually worked as a volunteer in the Paleontology department in Chicago at the Museum of Natural History.

SHUBINAwesome.

ROBINWe had to scan trays of gravel, looking for mammal bones. We used a microscope, because it was so hard to distinguish between the gravel and the bones. So, I don't know how you guys were finding it crawling on the ground, but...

SHUBINWell, it's just like you did back then. You train your eye. You know, you got better at it, right?

ROBINYeah, I did. I actually found ones.

SHUBINExactly.

ROBINThat was a big thing. Anyhow, my question had to do with something you were talking about earlier with the reptile jawbones migrating into the inner ear, which is also a source of balance. I don't know what the connection might be there, but I was curious about that. And also, the evolution of eyes. I can take my comment -- your comment off the air.

SHUBINOK, thank you.

NNAMDIOK, Robin, thank you very much for your call.

ROBINThanks.

SHUBINBoth great questions. So, when you think about the ear, there's really three components to our ear. There's the outside ear, called the external ear, which you can see. That’s the flap. Right? That's the flap we all see. We have two of them, hopefully. Then there's the middle ears, that set of bones and muscles in the middle that forms a lever system, that transducer the vibrations of the outer ear to the inside. Then, there's where all the sort of nervous tissue is and some other organs, in the inner ear.

SHUBINAnd our sense of balance, which is, you know, part of that link to hearing, actually sits in the inner ear area. And what it is is it's a set of very specialized structures, which have specialized sort of hair cells in them, that can bend in different ways when our body accelerates or when we bend our heads in different ways. And that's connected, that whole inner ear system, is connected to other parts of our body. In particular, muscles of our eyes and other parts of our body. So, this inner ear system is very important.

SHUBINAnd what we see is we can begin to trace that to other animals. And what you'll find is the fundamental organ unit of our inner ear, which, you know, plays a role in our balance, is also seen in fish. And it's seen in the outside of their body. It's an organ called the neuromast organ, and they sit in certain key parts of the body. And it gives a fish a sense of where it sits in space and the flow of water around it. So, again, we can see components of our ears, inner, outer, and middle, in other creatures. And even trace some of them deeper down, and not just to reptiles, but to fish.

NNAMDITelephones again. Maurice in Manassas, Virginia. Maurice, you're on the air. Go ahead, please.

MAURICEHello. Thank you for taking my call. I was at the HHMI Institute, I think a couple of years ago, you showed the Tiktaalik lectures. That's what I remember.

SHUBINYeah, I brought the head.

MAURICEYeah. A while ago. I was totally elated that you had written that book. The problem I've been having is trying to get copies of your book in Spanish and any form of copies of the fish. If we could get -- to teach people, because I have a lot of people that don't believe in evolution, and I want to show them that it can work, but they need something to see.

SHUBINThe book was published in Spain. I don't remember the name of the publisher. It was published in Spain, I think, three or four years ago in a Spanish translation. And we can -- it's posted on a website. Just type in tiktaalik.uchicago.edu. It'll give you a sense of what all the international language versions are. It may be available through Amazon. In terms of providing access to the fossil itself, one of the things that really helps us a lot in the world of paleontology is the ability now to scan things.

SHUBINSo, we have now scanned the head and fin of Tiktaalik in a high energy CT scanner, specialized for this kind of work. And we'll be putting online -- in fact, some of it is already. If you go to that tiktaalik.uchicago.edu website, what you'll see are scans of the fossils in three dimensions. And you can rotate the scans, you can look inside the skull. You can see the fin and take it apart in three dimensions and rotate each bone around, from the upper arm to the elbow to the wrist. So, digitally, we're making it all available. It's hard to make casts available, actually, because it involves a lot of man power.

SHUBINBut we can do the digital thing at the press of a button. And hopefully, shortly, within the next six months, we'll have databases where you can print them out on a 3D printer. And so, as 3D printing technology becomes more accessible and cheaper, we'll provide the tools to folks to be able to access the fossils that way.

NNAMDIMaurice, thank you for your call. By the way, Tiktaalik is spelled T-I-K-T-A-A-L-I-K. Is that correct?

SHUBINThat's correct. Yeah, I think.

NNAMDIThat's the way Tiktaalik is spelled if you're looking for it -- going to a website. Hernias. They seem to be another modern ailment that dates back to our evolution from fish. How so?

SHUBINIt's a great story, because if you look at fish, OK, and you dissect say, a shark, which we do in my -- I teach freshmen at the University of Chicago. And we, you know, we dissect a shark. And their little dogfish. And you take them apart, what you see is they have gonads. You know, the equivalent of testes and ovaries. But their gonads sit up near their heart. You see a pair and they're sitting up high in the body. They begin development there, and they stay there. If you look at a human embryo, we too have gonads that develop paired, and they begin their development up closer to the heart.

SHUBINAs we develop, we begin our development like a fish, but what happens is those testes, in the female ovaries, descend. And in males, they descend further than females. They descend to an external sack, the scrotum. And the reason why is our sperm are very temperature sensitive. And so what the scrotum is, that holds the testes, it enables the sperm to develop at a set temperature, right? It hangs outside the body and they can contract, raise and lower, if you will, to support the right temperature to support the development of sperm.

SHUBINBut, during development, our testes descend. We begin like a fish. And end up like a mammal. Well as those testes descend and form into a -- push into a scrotum, they essentially push out of the body wall during our development as males. And what that pushing out of the body wall does is it creates a weakness, a zone of weakness in a particular area called the inguinal area, which makes human males more susceptible to certain kinds of hernias than human females or other animals.

SHUBINSo what you see here is a defect that, you know, we have, which we experience as it goes wrong. And the reason for that is we begin our development like a fish, end our development like a mammal, all for good reasons, and that history comes back to bite us from time to time. In particular, in the sense that males are far weaker than females when it comes to certain parts of our abdominal wall. Lower abdominal wall.

NNAMDIBack to the telephones. And on to Emma in Washington, D.C. Hi, Emma.

EMMAHello. I have a question about the -- fish are cold blooded, and I was wondering about dolphins. Where do they fit in the picture? Is it the brain area of development with their communication skills and humans wanting to reach out to them, and they're open to contact with humans.

SHUBINThank you for your question. Yeah, so, dolphins, if you look at them, they're warm blooded. They're mammals. They have mammary glands. They're warm blooded. They have hair. If you look inside their fins, they have very mammal like -- flippers, I should say, they have very mammal like bones inside of them. Their brains are very mammal like. They're our close cousins. So, they're much closer cousins to us than say fish are, despite the fact that they're aquatic and have adapted in that context. They've re-entered the water as mammals.

SHUBINAnd as they've done so, they've done so with a mammalian brain. They've done so with a brain that is specialized in certain ways, for certain kinds of group behavior and communication. And it's a big brain. When you compare the relative size of the brain to the body, you know, dolphins come out pretty high. They give us a run for our money as humans, you know, quite a bit. So, there's a lot going on there. So, that cousin-ness you feel is because you are a very close cousin to dolphins. Actually, they're much closer than fish.

NNAMDIBarbara, thank you very much for your call. How does the modern complaint about back pain date back to our evolution from walking on all fours to walking upright?

SHUBINYeah, so if you look at our backs, it's -- we all suffer back pain at some point in our lives. And one of the big reasons for that is if you look at our back, it's not a straight series of vertebrae. Our back takes an S. You know? There's two bends in it. Three bends, actually, and it's a big S. And the problems we face sometimes occur because of that S shape. Well, what happened is you took an animal that was quadrupedal, walking on four legs, and as it evolved to become bipedal, the relationship, the center of mass, the center of gravity had to stay in line with the pelvis.

SHUBINBecause if it was in front of the body, you know, the animal would tip over, right? That wouldn't work. So, to keep the head aligned with the pelvis and the feet, the back had to take this S turn. So that's an important part of our ability to walk on two legs. But it's an important part of why our backs often suffer. So, you know, every evolutionary step is a trade off. Right? There are really fabulous things. Walking on two legs freed our hands, gave us a whole new vista of a world to explore. But it also has sequela and those sequelas are bad backs and other things.

NNAMDII'll go next to Barbara in Federalsburg, Maryland. Barbara, you are on the air. Go ahead, please.

BARBARAThank you for taking my call. I have a comment and a question. And my first comment is it reminds me of when the snake head came walking out of the pond in Laural.

NNAMDII knew this would come up.

BARBARAAnd came in to the other tributary.

NNAMDIAnd freaked us out, for some reason.

BARBARABut my question is, are we gonna continue to evolve, and what do you see as a human in the next 100,000 years?

SHUBINI love that question.

NNAMDIBefore Neil Shubin answers -- thank you very much for your call, Barbara.

BARBARAThank you, Kojo.

NNAMDIBefore Neil Shubin answers that, I will have Tina add her question to it. Tina, you're on the air. You only have about 30 seconds, but go ahead, please. Tina, are you there?

TINAYes, I am.

NNAMDIGo right ahead, please. Go right ahead, Tina.

TINAYes. What I wanted to ask was is there a visual prediction, through using the computer graphics, where we could visibly see like, where our body has come from through the -- from the fish, and through the future, you know, like a visual kind of a graphic where we could actually see, you know, what you have studied.

NNAMDIAnd where we're likely to be going in the future, Neil Shubin.

TINAYes. Yes. Definitely. Yes. What we would look like in the future.

SHUBINOK, so going -- let's just take this part. So, let's ask about the past and then the future. So, in terms of the past, yes, there are wonderful graphics where you can begin to look at our bodies and how they've been transformed over time. The show and its website does a lot of that. There was a big investment into the graphics to illuminate...

NNAMDIThat's where I spent my morning.

SHUBINAnd to illuminate how we got where we are. So, you'll see that, not just in the show, but in the website that's associated with the television show. Now, let's look at the question going forward, cause I think that's really fabulous. You know, if we took a time machine and came back, as you guys say, in 100,000 years, what would we look like? Well, that's a useful question to ask, and if you think about human performance, what we're capable of doing, what affects our cognitive capacity, our quality and length of life.

SHUBINAnd you think about what's really affecting that now. Is it Darwinian evolution? Well certainly, to some extent. Our bodies are still evolving. We are at a continual balance with the microbes that live around us and within us. And we're evolving every day, as a species. But there's another piece, and the real game changer here are human ideas. Human cultural practices. What we share as a species, in terms of our knowledge, with one another. Our social structures. We have a capacity to develop and disseminate technologies and ideas.

SHUBINAnd develop medicines and devices that improve and enhance our performance. So, I think, if we took a time machine and stepped off that time machine, what we'd see is that our evolution, over the next 100,000 years -- will, you know, will still have some Darwinian component, but Darwin has a new driver sitting next to him in the car. And that is human ideas and human innovation.

NNAMDINeil Shubin is a Paleontologist. He's Professor and Associate Dean of Biological Sciences at The University of Chicago. He's author of "Your Inner Fish: A Journey Into the 3.5 Billion Year History of the Human Body." And "The Universe Within: The Deep History of the Human Body." The PBS program called "Your Inner Fish" premieres April 9th on PBS. Neil Shubin, thank you so much for joining us.

SHUBINThank you.

NNAMDIAnd thank you all for listening. I'm Kojo Nnamdi.