“What does the body of a professor share with a blob?” Neil Shubin answers this and other questions about the evolutionary history of our anatomy in Your Inner Fish: A Journey Into The 3.5-Billion-Year History of the Human Body (Pantheon, 2008).
As an undergraduate student considering a research career in science, I once endured a 7 AM human anatomy course. In my semi-conscious state, breathing the slightly disturbing fumes of the preservative that the teaching assistant kept spraying on the cadavers, I was thinking, ‘this is morbidly fascinating, but really not that relevant to what scientists do today.’
If Neil Shubin had been teaching my anatomy course, I wouldn’t have struggled to get out of bed and make it to class on time. His book is a fun, compelling tour of the evolutionary history of the human body, filled with dozens of examples that nicely illustrate why our anatomy only makes real sense when it is understood in the context of evolution.
Neil Shubin is a professor of anatomy at the University of Chicago. He’s recently become famous for his team’s discovery of a major fossil: Tiktaalik, a spectacular intermediate between fish and land-dwelling tetrapods. Shubin’s find demonstrates the remarkable predictive power of evolutionary reasoning. He set out to find fossils that would tell us more about the origins of four-limbed land animals, a search which took him to Canada’s dry northern wilderness, where rocks from just the right time period and ancient environment lay exposed. Sure enough, there Shubin’s team found a fossil of a fish with wrists. In Your Inner Fish, Shubin recounts the story behind the Tiktaalik expedition, filling it in with entertaining anecdotes about how he learned to become a fossil-hunter.
Until reading Shubin’s book, I (in my ignorance of what paleontologists really do) hadn’t thought of paleontologists as real biologists. There is only so much you can learn about biology by looking at rocks, I thought. Shubin shows us that good paleontologists do what any good scientist does; they use any tool available to answer a pressing scientific question. Paleontologists need to know enough geology to work intelligently with fossils, but to make sense of those fossils they also need to be well versed in the anatomy of living animals. On top of that, today’s paleontologists need to understand genes as well. Shubin is interested in the evolutionary development of limbs. To study how limbs evolved, he not only scours desolate wilderness for fossils; he also uses the molecular tools of modern developmental biology to study limb development in live embryos.
Shubin’s lab studies shark and skate embryos. In his book, he details some of the pioneering experiments of developmental biology, in which researchers were able to identify various genes involved in limb development in birds, amphibians, and mammals. But if birds, amphibians, and mammals all descended from fish ancestors, how did they obtain genes that enable them to develop arms and legs? Shubin has addressed this question by looking at what these limb-development genes do in fish. The result of his experiments (and those of other labs) are not surprising (if you’ve followed any molecular biology in the last 30 years) but incredibly profound: fish use the same genes to make fins that mammals use to make limbs. The transition from fins to limbs did not require new genes; it just required that existing genes be used in novel ways.
The big question Shubin is after in his book is stated clearly in the epilogue: “What do billions of years of history mean for our lives today?” He walks us through the evolutionary history of our wrists, teeth, jaws, skull, eyes, ears, and our sense of smell. He explains how men are prone to hernias because of our evolutionary history (sharks have their testes in their ‘chests’, right behind the gills; somewhere in our evolutionary history testes started to move downward, leading to an anatomical compromise that makes a weak spot around the groin). All along the way, Shubin genially explains how evidence from fossils, genes, and today’s living species enables scientists to piece this history together. By the end of the book, readers should be persuaded that the evidence for our evolutionary history is not just overwhelming, it’s also extremely relevant for understanding how and why the human body works the way it does.
In our society, discussions of evolution can get acrimonious, and evolutionary biologists are often tempted to focus their popular writing on rebutting the claims of creationists. Neil Shubin takes a different tack; he’s not polemical in this book, and he doesn’t explicitly attack creationism. Instead he’s like Bill Nye The Science Guy - infectiously excited about his subject, happy to show you all of the amazing stuff that scientists have been able to figure out about how our bodies took their modern form. Writing like this is a sure way of inspiring the next generation of scientists.
In fact, one of my main criticisms of the book is that it is often aimed a little too much at the next generation: nerdy middle school kids would be able to easily follow the book, while adult readers of popular science books will find the tone of the writing frequently pitched too low. When I read books by Richard Dawkins, Roger Penrose, or Brian Greene, I enjoy the language and style as well as the substance. Reading Your Inner Fish, I wished that Shubin had expected more of his readers. Explanations were often very simplified, and in a few places the book could have used a more in-depth follow up discussion of the implications of an experiment or fossil finding. There could be an advantage to this, however; the book is easy to read and is thus more likely to reach a broader readership, including many readers who typically wouldn’t pick up a book on evolution.
On a few occasions, Shubin’s efforts to simplify can mislead readers. Finding the right semantic shortcuts to talk about evolution can be devilishly tricky, and if you choose the wrong ones it is easy to reinforce popular misconceptions about evolution. Shubin uses “your inner fish” to talk about our evolutionary kinship with fish, and our fish ancestors, but as Ryan Gregory has pointed out, this is taken too far when Shubin talks about an “inner fly” and an “inner chicken” - we share ancestors with flies and chickens, but at no point did we ever have an ancestor that was a fly or a chicken (or any kind of bird or insect). In another place, we’re told we can thank the modern species Amphioxus for our susceptibility to slipped disks in our backs. Amphioxus, a worm with a notochord, in many ways resembles some ancient species of primitive chordates, but the modern animal of course is not our ancestor.
Another common misconception about evolution that I wish Shubin had done more to dispel is the idea that we’re the inevitable outcome of evolutionary progress directed at making us. We are the product of an evolutionary history, and thus one can naturally trace the historical development of our features in the fossil record. And there are many ‘living fossil’ species, species whose features seem to have hardly changed over hundreds of millions of years of evolution, which make great examples of what ancient, transitional species probably looked like. But modern amphibians and reptiles, while they share many features of our common ancestors, are just as ‘evolved’ as we are. Readers who come in with the misconception that the whole point of evolutionary history was to create us will probably finish Your Inner Fish with that misconception still in place. True, the book is about our evolutionary history, but I think it would have helped to put more emphasis on the fact that we are just one of many lines of remarkable evolutionary innovation.
On the whole though, this is an entertaining and useful book, especially for readers who don’t often read longer and more dense works of popular science. Shubin is a clear and entertaining guide, cracking jokes along the way, showing us just how much fun it is to study evolution. Given the public’s wide skepticism and lack of understanding of evolutionary biology, we need more books like Your Inner Fish. Shubin emphasizes that evolution is a predictive science that rests on a very strong foundation of evidence. He also shows how our evolutionary history tells us about ourselves today. Humans have always been obsessed with the big question, “Where do we come from?” If you show people that evolutionary biology has interesting and meaningful answers to this question, their resistance to one of the greatest scientific theories we have may eventually fade away.