Oliver Sacks on Your Inner Fish
Since the 1970 publication of Migraine, neurologist Oliver Sacks's unusual and fascinating case histories of "differently brained" people and phenomena--a surgeon with Tourette's syndrome, a community of people born totally colorblind, musical hallucinations, to name a few--have been marked by extraordinary compassion and humanity, focusing on the patient as much as the condition. His books include The Man Who Mistook His Wife for a Hat, Awakenings (which inspired the Oscar-nominated film), and 2007's Musicophilia. He lives in New York City, where he is Professor of Clinical Neurology at Columbia University.
Your Inner Fish is my favorite sort of book--an intelligent, exhilarating, and compelling scientific adventure story, one which will change forever how you understand what it means to be human.
The field of evolutionary biology is just beginning an exciting new age of discovery, and Neil Shubin's research expeditions around the world have redefined the way we now look at the origins of mammals, frogs, crocodiles, tetrapods, and sarcopterygian fish--and thus the way we look at the descent of humankind. One of Shubin's groundbreaking discoveries, only a year and a half ago, was the unearthing of a fish with elbows and a neck, a long-sought evolutionary "missing link" between creatures of the sea and land-dwellers.
My own mother was a surgeon and a comparative anatomist, and she drummed it into me, and into all of her students, that our own anatomy is unintelligible without a knowledge of its evolutionary origins and precursors. The human body becomes infinitely fascinating with such knowledge, which Shubin provides here with grace and clarity. Your Inner Fish shows us how, like the fish with elbows, we carry the whole history of evolution within our own bodies, and how the human genome links us with the rest of life on earth.
Shubin is not only a distinguished scientist, but a wonderfully lucid and elegant writer; he is an irrepressibly enthusiastic teacher whose humor and intelligence and spellbinding narrative make this book an absolute delight. Your Inner Fish is not only a great read; it marks the debut of a science writer of the first rank.
(Photo © Elena Seibert)
A Note from Author Neil Shubin
This book grew out of an extraordinary circumstance in my life. On account of faculty departures, I ended up directing the human anatomy course at the University of Chicago medical school. Anatomy is the course during which nervous first-year medical students dissect human cadavers while learning the names and organization of most of the organs, holes, nerves, and vessels in the body. This is their grand entrance to the world of medicine, a formative experience on their path to becoming physicians. At first glance, you couldn't have imagined a worse candidate for the job of training the next generation of doctors: I'm a fish paleontologist.
It turns out that being a paleontologist is a huge advantage in teaching human anatomy. Why? The best roadmaps to human bodies lie in the bodies of other animals. The simplest way to teach students the nerves in the human head is to show them the state of affairs in sharks. The easiest roadmap to their limbs lies in fish. Reptiles are a real help with the structure of the brain. The reason is that the bodies of these creatures are simpler versions of ours.
During the summer of my second year leading the course, working in the Arctic, my colleagues and I discovered fossil fish that gave us powerful new insights into the invasion of land by fish over 375 million years ago. That discovery and my foray into teaching human anatomy led me to a profound connection. That connection became this book.
Click on thumbnails for larger images
The crew removing the first Tiktaalik in 2004 Ted Daeschler and Neil Shubin propecting for new sites (Credit: Andrew Gillis) The valley where Tiktaalik was discovered (credit: Ted Daeschler, Academy of Natural Sciences)
The models of Tiktaalik being constructed for exhibition (Tyler Keillor, University of Chicago) Me with one of the models (John Weinstein, Field Museum)
Neil Shubin, Professor of Biology and Anatomy at the University of Chicago, made headlines in April 2006 with his discovery of a 375-million-year-old fossil called Tiktaalik, the missing link between ancient sea creatures and land dwellers. The reviewers, mostly science writers, embraced Shubins popular science book, which offers a new perspective on evolution, a subject on which most people feel like theyve already made up their minds. While many Americans doubt Darwinism, hardly anyone discounts anatomy, so it is a logical place to reopen the debate. All critics agreed that Shubin, with his clear examples and explanations, makes (yet another) convincing argument. A few critics, in fact, were so excited by it that they seemed ready to enroll in Shubins anatomy course themselves.
Copyright © 2004 Phillips & Nelson Media, Inc.
Review
“A delightful introduction to our skeletal structure, viscera and other vital parts—and evidence that learning the secrets of the human body need not unhinge you. . . . [Shubin] is a warm and disarming guide. . . . Future researchers, aware that the ingredients of our evolutionary precursors are part of the human recipe, may well find new ways to prevent the wear and tear on our fish-begotten bodies. And who knows? Maybe one or two of them will have had their first taste of the marvels of human evolution in Neil Shubin’s anatomy class.” —Los Angeles Times
“With infectious enthusiasm, unfailing clarity, and laugh-out-loud humor, Neil Shubin has created a book on paleontology, genetics, genomics, and anatomy that is almost impossible to put down. In telling the story of why we are who we are, Shubin does more than show us our inner fish; he awakens and excites the inner scientist in us all.” —Pauline Chen, author of Final Exam
“Your Inner Fish is my favorite sort of book—an intelligent, exhilarating, and compelling scientific adventure story, one which will change forever how you understand what it means to be human. . . . Shubin is not only a distinguished scientist, but a wonderfully lucid and elegant writer; he is an irrepressibly enthusiastic teacher whose humor and intelligence and spellbinding narrative make this book an absolute delight. Your Inner Fish is not only a great read; it marks the debut of a science writer of the first rank.” —Oliver Sacks, Amazon.com
“The antievolution crowd is always asking where the missing links in the descent of man are. Well, paleontologist Shubin actually discovered one. . . . A crackerjack comparative anatomist, he uses his find to launch a voyage of discovery about the evolutionary evidence we can readily see at hand. . . . Shubin relays all this exciting evidence and reasoning so clearly that no general-interest library should be without this book.” —Booklist (starred review)
“A skillful writer, paleontologist Shubin conveys infectious enthusiasm. . . . Even readers with only a layperson’s knowledge of evolution will learn marvelous things about the unity of all organisms since the beginning of life.” —Kirkus Reviews (starred review)
“Fish paleontologist Shubin illuminates the subject of evolution with humor and clarity in this compelling look at how the human body evolved into its present state. . . . Shubin moves smoothly through the anatomical spectrum. . . . [He] excels at explaining the science, making each discovery an adventure.”
—Publishers Weekly
“I was hooked from the first chapter of Your Inner Fish. Creationists will want this book banned because it presents irrefutable evidence for a transitional creature that set the stage for the journey from sea to land. This engaging book combines the excitement of discovery with the rigors of great scholarship to provide a convincing case of evolution from fish to man.”
—Don Johanson, director, Institute of Human Origins; discoverer of “Lucy”
“In this extraordinary book, Neil Shubin takes us on an epic expedition to arctic wastelands, where his team discovered amazing new fossil evidence of creatures that bridge the gap between fish and land-living animals. . . .With clarity and wit, Shubin shows us how exciting it is to be in the new age of discovery in evolutionary biology.”
—Mike Novacek, author of Terra: Our 100 Million Year Ecosystem and the Threats That Now Put It at Risk
"Cleverly weaving together adventures in paleontology with very accessible science, Neil Shubin reveals the many surprisingly deep connections between our anatomy and that of fish, reptiles, and other creatures. You will never look at your body in the same way again--examine, embrace, and exalt Your Inner Fish!"
—Sean Carroll, author of The Making of Fittest and Endless Forms Most Beautiful
"If you thought paleontology was all about Jurassic Park, take a look at this eye-opening book. Shubin takes us back 375 million years, to a time when a strange fish-like creature swam (or crawled) in shallow streams. Come along on this thrilling paleontological journey and learn how living things--including you--got to be what they are."
—Richard Ellis, author of Encyclopedia of the Sea
"The human story didn't start with the first bipeds; it began literally billions of years ago. In this easy-reading volume, Shubin shows us how to discover that long and fascinating history in the structure of our own bodies while weaving in a charming account of his own scientific journey. This is the ideal book for anyone who wants to explore beyond the usual anthropocentric account of human origins."
—Ian Tattersall, curator, American Museum of Natural History
About the Author
NEIL SHUBIN is provost of The Field Museum as well as a professor of anatomy at the University of Chicago, where he also serves as an associate dean. Educated at Columbia, Harvard, and the University of California at Berkeley, he lives in Chicago.
From The Washington Post
Reviewed by Barbara J. King
For the first time, Americans have the chance to meet an ancient ancestor. Lucy, the famous 3.2-million-year-old, human-like fossil from Ethiopia, is here on tour. For the next six years, you can visit her at museums across the country and stare into the mirror of your own past.
But in Your Inner Fish, Neil Shubin describes a fossil named Tiktaalik that makes Lucy's time on Earth seem like just yesterday. At 375 million years old, Tiktaalik (which means "large freshwater fish" in Inuit) sports a curious mix of features that mark it as an evolutionary milestone, a "beautiful intermediate between fish and land-living animals." In its fossilized bones, we see a flat head and body, a functional neck and other features that presage what's to come, all mixed in with fish features like fins and scales. Most surprising of all, Tiktaalik has a wrist joint. "Bend your wrist back and forth," Shubin instructs his readers. "Open and close your hand. When you do this, you are using joints that first appeared in the fins of fish like Tiktaalik."
Shubin, a paleontologist and professor of anatomy, made the astounding discovery of Tiktaalik, the first find of its kind, with colleagues in the Canadian Arctic in 2004. He has clearly fallen in love with this ancient fish, and conveys its significance with both precision and exuberance. "Seeing Lucy," writes Shubin, "we can understand our history as highly advanced primates. Seeing Tiktaalik is seeing our history as fish." In fact, Shubin wants us to see our history not only as primates and fish, but also as insects and worms. Exploring the 3.5-billion-year history of life on Earth, Shubin says, will yield a deeper grasp of how our bodies came to be what they are. "Inside our bodies are connections to a menagerie of other creatures. Some parts resemble parts of jellyfish, others parts of worms, still others parts of fish. These aren't haphazard similarities. . . . It is deeply beautiful to see that there is an order in all these features."
Shubin, then, turns Tiktaalik the ancient fish into a poster fossil for the elegant connections across all life-forms on our planet. This evolutionary continuity, so basic to biology, paleontology and anthropology, is the real message of the book. Shubin reveals its practical applications: The better we understand the long history of our joints and organs, the better we will be able to treat trauma and disease in our bodies.
Genes are the co-stars, with bones, of Your Inner Fish. As Shubin puts it, "DNA is an extraordinarily powerful window into life's history and the formation of bodies and organs." When scientists make a fly that lacks a certain gene, the fly's midsection is missing or altered. Frankenstein-like research of this nature helps scientists to understand more about how genes influence developmental processes. Yet how relevant is such research for understanding human development, which unfolds according to rich interaction between our genes and our environment? It's hard not to wince when thinking about the subjects of this DNA-altering lab work.
Nevertheless, Shubin's melding of fossil and genetic data is deft, and it prepares us for his central conclusion. Our lives reflect the evolutionary principle of descent with modification: "Looking back through billions of years of change, everything innovative or apparently unique in the history of life is really just old stuff that has been recycled, repurposed, or otherwise modified for new uses." How our senses work, why we get sick and even why we get the hiccups can be explained by this principle. For instance, hiccups are inherited from fish and tadpoles. We hiccup when a nerve spasm causes muscles in the diaphragm, neck and throat to contract. We gasp and take in some air, and the glottis in the back of our throat snaps shut. This tortuous path that nerves take in our body and the brain stem's response when they spasm are marvelous adaptations for gill-breathers, Shubin explains, but not entirely ideal for us.
Shubin's message convinces. Read Your Inner Fish, and you'll never again be able to look a fish in the eye (or eat seafood) without thinking about shared evolution. In two ways, though, Shubin takes a good thing too far. His passion for science enlivens every page, but some of his sentences ("True, big fish tend to eat littler fish") are overly simplified. He could have trusted his readers more.
Even more worrisome is Shubin's tendency to oversell the relatedness of fish and humans. Our common ancestry with apes is far more recent than with fish, and as a result, our inner ape dominates our inner fish. This fact is most evident when we consider behavior as well as anatomy. Do fish empathize with sick companions, grieve for dead ones or express empathy? Certainly not to the extent that apes do. Or consider the wrist joint which, as we have seen, Shubin uses to link Tiktaalik with humans. Enhanced mobility of the ape wrist joint allows chimpanzees and gorillas to gesture in ways more varied and expressive even than monkeys, a capacity that in turn enriches social communication among them.
We humans are first and foremost primates. Nevertheless, Shubin is dead right: The elegance and full emotional power of our connection with the natural world compel us to reach further back in time and deeper into the Earth's fossil layers. Visit Lucy, think Tiktaalik, and feel the connection.
Copyright 2008, The Washington Post. All Rights Reserved.
Excerpt. © Reprinted by permission. All rights reserved.
FINDING YOUR INNER FISH
Typical summers of my adult life are spent in snow and sleet, cracking rocks on cliffs well north of the Arctic Circle. Most of the time I freeze, get blisters, and find absolutely nothing. But if I have any luck, I find ancient fish bones. That may not sound like buried treasure to most people, but to me it is more valuable than gold.
Ancient fish bones can be a path to knowledge about who we are and how we got that way. We learn about our own bodies in seemingly bizarre places, ranging from the fossils of worms and fish recovered from rocks from around the world to the DNA in virtually every animal alive on earth today. But that does not explain my confidence about why skeletal remains from the past—and the remains of fish, no less—offer clues about the fundamental structure of our bodies.
How can we visualize events that happened millions and, in many cases, billions of years ago? Unfortunately, there were no eyewitnesses; none of us was around. In fact, nothing that talks or has a mouth or even a head was around for most of this time. Even worse, the animals that existed back then have been dead and buried for so long their bodies are only rarely preserved. If you consider that over 99 percent of all species that ever lived are now extinct, that only a very small fraction are preserved as fossils, and that an even smaller fraction still are ever found, then any attempt to see our past seems doomed from the start.
DIGGING FOSSILS—SEEING OURSELVES
I first saw one of our inner fish on a snowy July afternoon while studying 375-million-year-old rocks on Ellesmere Island, at a latitude about 80 degrees north. My colleagues and I had traveled up to this desolate part of the world to try to discover one of the key stages in the shift from fish to land-living animals. Sticking out of the rocks was the snout of a fish. And not just any fish: a fish with a flat head. Once we saw the flat head we knew we were onto something. If more of this skeleton were found inside the cliff, it would reveal the early stages in the history of our skull, our neck, even our limbs.
What did a flat head tell me about the shift from sea to land? More relevant to my personal safety and comfort, why was I in the Arctic and not in Hawaii? The answers to these questions lie in the story of how we find fossils and how we use them to decipher our own past.
Fossils are one of the major lines of evidence that we use to understand ourselves. (Genes and embryos are others, which I will discuss later.) Most people do not know that finding fossils is something we can often do with surprising precision and predictability. We work at home to maximize our chances of success in the field. Then we let luck take over.
The paradoxical relationship between planning and chance is best described by Dwight D. Eisenhower’s famous remark about warfare: “In preparing for battle, I have found that planning is essential, but plans are useless.” This captures field paleontology in a nutshell. We make all kinds of plans to get us to promising fossil sites. Once we’re there, the entire field plan may be thrown out the window. Facts on the ground can change our best-laid plans.
Yet we can design expeditions to answer specific scientific questions. Using a few simple ideas, which I’ll talk about below, we can predict where important fossils might be found. Of course, we are not successful 100 percent of the time, but we strike it rich often enough to make things interesting. I have made a career out of doing just that: finding early mammals to answer questions of mammal origins, the earliest frogs to answer questions of frog origins, and some of the earliest limbed animals to understand the origins of land-living animals.
In many ways, field paleontologists have a significantly easier time finding new sites today than we ever did before. We know more about the geology of local areas, thanks to the geological exploration undertaken by local governments and oil and gas companies. The Internet gives us rapid access to maps, survey information, and aerial photos. I can even scan your backyard for promising fossil sites right from my laptop. To top it off, imaging and radiographic devices can see through some kinds of rock and allow us to visualize the bones inside.
Despite these advances, the hunt for the important fossils is much what it was a hundred years ago. Paleontologists still need to look at rock—literally to crawl over it—and the fossils within must often be removed by hand. So many decisions need to be made when prospecting for and removing fossil bone that these processes are difficult to automate. Besides, looking at a monitor screen to find fossils would never be nearly as much fun as actually digging for them.
What makes this tricky is that fossil sites are rare. To maximize our odds of success, we look for the convergence of three things. We look for places that have rocks of the right age, rocks of the right type to preserve fossils, and rocks that are exposed at the surface. There is another factor: serendipity. That I will show by example.
Our example will show us one of the great transitions in the history of life: the invasion of land by fish. For billions of years, all life lived only in water. Then, as of about 365 million years ago, creatures also inhabited land. Life in these two environments is radically different. Breathing in water requires very different organs than breathing in air. The same is true for excretion, feeding, and moving about. A whole new kind of body had to arise. At first glance, the divide between the two environments appears almost unbridgeable. But everything changes when we look at the evidence; what looks impossible actually happened.
In seeking rocks of the right age, we have a remarkable fact on our side. The fossils in the rocks of the world are not arranged at random. Where they sit, and what lies inside them, is most definitely ordered, and we can use this order to design our expeditions. Billions of years of change have left layer upon layer of different kinds of rock in the earth. The working assumption, which is easy to test, is that rocks on the top are younger than rocks on the bottom; this is usually true in areas that have a straightforward, layer-cake arrangement (think the Grand Canyon). But movements of the earth’s crust can cause faults that shift the position of the layers, putting older rocks on top of younger ones. Fortunately, once the positions of these faults are recognized, we can often piece the original sequence of layers back together.
The fossils inside these rock layers also follow a progression, with lower layers containing species entirely different from those in the layers above. If we could quarry a single column of rock that contained the entire history of life, we would find an extraordinary range of fossils. The lowest layers would contain little visible evidence of life. Layers above them would contain impressions of a diverse set of jellyfish-like things. Layers still higher would have creatures with skeletons, appendages, and various organs, such as eyes. Above those would be layers with the first animals to have backbones. And so on. The layers with the first people would be found higher still. Of course, a single column containing the entirety of earth history does not exist. Rather, the rocks in each location on earth represent only a small sliver of time. To get the whole picture, we need to put the pieces together by comparing the rocks themselves and the fossils inside them, much as if working a giant jigsaw puzzle.
That a column of rocks has a progression of fossil species probably comes as no surprise. Less obvious is that we can make detailed predictions about what the species in each layer might actually look like, by comparing them with species of animals that are alive today; this information helps us to predict the kinds of fossils we will find in ancient rock layers. In fact, the fossil sequences in the world’s rocks can be predicted by comparing ourselves with the animals at our local zoo or aquarium.
How can a walk through the zoo help us predict where we should look in the rocks to find important fossils? A zoo offers a great variety of creatures that are all distinct in many ways. But let’s not focus on what makes them distinct; to pull off our prediction, we need to focus on what different creatures share. We can then use the features common to all species to identify groups of creatures with similar traits. All the living things can be organized and arranged like a set of Russian nesting dolls, with smaller groups of animals comprised in bigger groups of animals. When we do this, we discover something very fundamental about nature.
Every species in the zoo and the aquarium has a head and two eyes. Call these species “Everythings.” A subset of the creatures with a head and two eyes has limbs. Call the limbed species “Everythings with limbs.” A subset of these headed and limbed creatures has a huge brain, walks on two feet, and speaks. That subset is us, humans. We could, of course, use this way of categorizing things to make many more subsets, but even this threefold division has predictive power.
The fossils inside the rocks of the world generally follow this order, and we can put it to use in designing new expeditions. To use the example above, the first member of the group “Everythings,” a creature with a head and two eyes, is found in the fossil record well before the first “Everything with limbs.” More precisely, the first fish (a card-carrying member of the “Everythings”) appears before the first amphibian (an “Everything with limbs”). Obviously, we refine this by looking at more kinds of animals and many more characteristics that groups of them share, as well as by assessing the actual age of the rocks themselves.
In our labs, we do exactly this type of analysis with thousands upon thousands of characteristics and species. We look at every bit of anatomy we can, and often at large chunks of DNA. There are so much data that we often need powerful computers to show us the groups within groups. This approach is the foundation of biology, because it enables us to make hypotheses about how creatures are related to one another.
Besides helping us refine the groupings of life, hundreds of years of fossil collection have produced a vast library, or catalogue, of the ages of the earth and the life on it. We can now identify general time periods when major changes occurred. Interested in the origin of mammals? Go to rocks from the period called the Early Mesozoic; geochemistry tells us that these rocks are likely about 210 million years old. Interested in the origin of primates? Go higher in the rock column, to the Cretaceous period, where rocks are about 80 million years old.
The order of fossils in the world’s rocks is powerful evidence of our connections to the rest of life. If, digging in 600-million-year-old rocks, we found the earliest jellyfish lying next to the skeleton of a woodchuck, then we would have to rewrite our texts. That woodchuck would have appeared earlier in the fossil record than the first mammal, reptile, or even fish—before even the first worm. Moreover, our ancient woodchuck would tell us that much of what we think we know about the history of the earth and life on it is wrong. Despite more than 150 years of people looking for fossils—on every continent of earth and in virtually every rock layer that is accessible—this observation has never been made.
Let’s now return to our problem of how to find relatives of the first fish to walk on land. In our grouping scheme, these creatures are somewhere between the “Everythings” and the “Everythings with limbs.” Map this to what we know of the rocks, and there is strong geological evidence that the period from 380 million to 365 million years ago is the critical time. The younger rocks in that range, those about 360 million years old, include diverse kinds of fossilized animals that we would all recognize as amphibians or reptiles. My colleague Jenny Clack at Cambridge University and others have uncovered amphibians from rocks in Greenland that are about 365 million years old. With their necks, their ears, and their four legs, they do not look like fish. But in rocks that are about 385 million years old, we find whole fish that look like, well, fish. They have fins, conical heads, and scales; and they have no necks. Given this, it is probably no great surprise that we should focus on rocks about 375 million years old to find evidence of the transition between fish and land-living animals.
We have settled on a time period to research, and so have identified the layers of the geological column we wish to investigate. Now the challenge is to find rocks that were formed under conditions capable of preserving fossils. Rocks form in different kinds of environments and these initial settings leave distinct signatures on the rock layers. Volcanic rocks are mostly out. No fish that we know of can live in lava. And even if such a fish existed, its fossilized bones would not survive the superheated conditions in which basalts, rhyolites, granites, and other igneous rocks are formed. We can also ignore metamorphic rocks, such as schist and marble, for they have undergone either superheating or extreme pressure since their initial formation. Whatever fossils might have been preserved in them have long since disappeared. Ideal to preserve fossils are sedimentary rocks: limestones, sandstones, siltstones, and shales. Compared with volcanic and metamorphic rocks, these are formed by more gentle processes, including the action of rivers, lakes, and seas. Not only are animals likely to live in such environments, but the sedimentary processes make these rocks more likely places to preserve fossils. For example, in an ocean or lake, particles constantly settle out of the water and are deposited on the bottom. Over time, as these particles accumulate, they are compressed by new, overriding layers. The gradual compression, coupled with chemical processes happening inside the rocks over long periods of time, means that any skeletons contained in the rocks stand a decent chance of fossilizing. Similar processes happen in and along streams. The general rule is that the gentler the flow of the stream or river, the better preserved the fossils.
