A review of Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body by Neil Shubin
256 pages.
Vintage

We can walk because we have teeth. More than 500 million years ago, in some primordial sea, a soft-bodied, worm-like creature developed hard, pointed growths inside its mouth. These growths were a mutation, a freak accident in the replication of its genetic code, but they proved quite useful when it came to eating other soft-bodied, worm-like creatures. The code for these hard growths was passed on, and over eons, it was muddled even more. Eventually mutants arose with hard growths that covered their entire heads, and these new features also came in handy—this time to fend off all the soft-bodied, worm-like creatures swimming about with big teeth. After this, the genetic code for the hard structures continued to morph, giving rise over the ages to backbones, ribs, fins, and then, some 375 million years ago, legs.

Your Inner Fish comes in the aftermath of Neil Shubin’s historic co-discovery of Tiktaalik, a “found link” between prehistoric fish and the world’s first amphibians. Shubin, a paleontologist and professor of anatomy at the University of Chicago, found the fossil in 2004, after years of scouring Devonian aged sedimentary rocks in the high arctic of Ellesmere Island, right where a chronological sandwiching of other fossils said it should be. In this quick, enlightening, and entertaining read, Shubin recounts the motivation for hunting for Tiktaalik and the details of its discovery, and then he uses this “fish with wrists” as a jumping off point for a discussion—conversational in tone but compelling in content—on the origins and implications of many of our distinguishing features.

Shubin peers into our bodies in the same way that Carl Sagan once gazed out at the universe. “If you know how to look,” he writes, “our body becomes a time capsule.” It “tells of critical moments in the history of our planet and of a distant past in ancient oceans, streams and forests.” Citing evidence from the fields of paleontology, molecular biology, anatomy, and genetics, he traces our bodies back across milestones in our evolutionary history, through the environments they came from and the purposes they once served.

The book has a segmented structure, with each chapter focusing on a different body part: our hands, our teeth, our heads, our bones, our noses, eyes, and ears. Through these examples, and through vivid anecdotes of his own experiences studying anatomy and paleontology, Shubin builds a picture of the human body not as DaVinci’s model of form, function, and near-perfection, but rather as a “hot-rod Beetle,” an old clunker of a machine, jury-rigged by evolution to perform whatever task it needs to by using whatever it has available. The delicate bones of the mammalian middle ear, for example, are vestiges of bones from the reptile’s jaw structure, come together with an earlier leftover from the fish’s gill arch to form an apparatus that is very well suited to hearing in air.

This pattern of descent with modification, from cells to blobs to worms and so on through to humans, inevitably accrues a good deal of anatomical detritus as it pushes through the ages, with unused genes and body parts getting passed along nonetheless. In his chapter on scent, Shubin points out that a full three percent of the human genome is devoted to our sense of smell, much of it coding for aromas that we can no longer detect. Our primate ancestors dropped the required receptors when the world’s forests first blossomed into colorful fruit, and thus putting resources towards seeing vivid reds, yellows, blues, and oranges became a higher priority for survival. The genes for these forgotten smells, however, have stayed in our DNA. “This baggage is a silent witness to our past,” says Shubin, “inside our noses is a veritable tree of life.”

It’s not until the end of the book though that Shubin really revs up his point. In a chapter entitled “The Meaning of it All,” he notes that many of our physical ailments, from hernias and hemorrhoids to hiccups and heart disease, can be explained by examining our inner fish, and our other distant relatives. Hernias of the groin, for example, come about due to a weakness in the body’s muscular wall where the testes have descended through. They might have formed down there in the first place, saving everybody trouble, but by looking back at sharks and comparing the similarities in our embryos, we can see that they’re descending from the position where they first evolved, up near the liver, where they still form in our embryos. Hiccups, on a different note, are ticks of the nervous system, brought about by our brain’s lingering desire to breathe through its long departed gills.

Ultimately, the book comes together to form a strong case against there being any kind of logical design inherent in our bodies, apart from the logic of necessity. Throughout the text, there is a notable absence of any reference to God or religion. Shubin simply explains his case as an inescapable conclusion following the masses of data from very different fields of science that all converge on this idea: “Our fish-to-human framework is so strongly supported that we no longer try to marshal evidence for it—doing so would be like dropping a ball fifty times to test the theory of gravity,” he writes. “You would have the same chance of seeing your ball go up on the fifty-first time you dropped it as you would of finding strong evidence against these relationships.” Your Inner Fish isn’t an attack on intelligent design; it simply leaves no room for it.

But the arguments that Shubin puts forward are hardly new. Such lines of reasoning constitute some of the fundamental motivation underlying scientific acceptance of evolution, and books like The Ancestor’s Tale by Richard Dawkins, or his most recent piece, The Greatest Show on Earth, expound the theme. Nevertheless, what sets Shubin apart is his friendly voice and his clear explanation of the facts from which he builds his ideas. While his first book may not resonate as strongly with advocates of evolution as do Dawkins’ polished works, I’d argue that it presents an account that opponents of evolution are much more likely to dwell on.

My criticisms of the Shubin’s book are entirely literary, quibbles of structure and style. He has a gift with clear, simple language, to be sure, and his work is punctuated with interesting facts, colorful side stories, and frequent bursts of hilarity—but as he writes, he remains a scientist. There is a formality to his structure; each chapter follows more or less the same course as the others, beginning with an anecdote and then a quick, explicit overview of the chapter’s upcoming contents before the next plunge into in paleontology, anatomy, and molecular biology. Transitions from section to section often take on a question-and-answer form, which gets repetitive very quickly. In short, the book’s wires are showing.

A few times, the repetitive style grew tiring, but for the most part, Shubin’s lucid account of our anatomical history was just too interesting to ignore. It’s not a perfect book, but then, we don’t have perfect bodies. And I have to admit, like the human body, Your Inner Fish is simply fantastic for how it gets the job done.