Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body, by Neil Shubin. New York: Pantheon Books, 2008. 240 pp. $24.00 (cloth).
In 2006, Neil Shubin made history when he announced his discovery of a “missing link”: a new fossil species showing characteristics that bridge the evolutionary gap between two different types of organisms. He named it Tiktaalik.
[F]or me the greatest moment of the whole media blitz was . . . at my son’s preschool. . . . The first child said it was a crocodile or an alligator. When queried why, he said that like a crocodile or lizard it has a flat head with eyes on top. Big teeth, too. Other children started to voice their dissent. Choosing the raised hand of one of these kids, I heard: No, no it isn’t a crocodile, it is a fish, because it has scales and fins. Yet another child shouted “Maybe it is both.” Tiktaalik’s message is so straightforward even preschoolers can see it (p. 25).
Your Inner Fish seeks to reveal the evolutionary history of humans as we travel down the branches of our family tree toward its trunk, passing fossils such as Tiktaalik and finding our “inner fish” along the way.
Shubin makes this story accessible by maintaining a tight focus on the essentials of each topic while minimizing his use of technical terms. He uses analogy well in clarifying points; for instance, he compares the complexity of a smell made of many molecules to a musical chord made of many notes (p. 141), and compares the function of an inner ear bone to a plunger (p. 158). And he generally makes effective use of humor; for example, of searching for fossils, he writes: “Volcanic rocks are mostly out. No fish that we know of can live in lava” (p. 10). On waiting for monthly shipments of rare eggs for embryological research: “We became a virtual cargo cult as we waited” (p. 56). And on the alignment of teeth in mammals: “A mismatch between upper and lower teeth can shatter our teeth, and enrich our dentist” (p. 61). His droll style even affects some of his chapter titles, such as “Handy Genes” for the chapter on genetics of hand development, and “Getting Ahead” for the chapter on the head.
The book is extensively illustrated, including a reproduction of the map in a geology textbook that led Shubin to the site where he discovered Tiktaalik (p. 16), photos and drawings of the Tiktaalik fossil (pp. 23 and 24), a drawing comparing the gill arches of a human fetus to the adult structures derived from them (p. 88), and a figure showing the similarities between the cranial nerves of sharks and of humans (p. 92). There are forty-five figures (in a book of just 201 pages), most of which are line drawings commissioned specifically for the book, and they substantially aid the text in conveying the elements of each subject.
All of these factors combine to make the book engaging and highly readable for those with little or no background in biology. This is all the more impressive given the book’s vast scope, which includes material not only on paleontology and human anatomy (anticipated by the title), but also on genetics, embryology, human physiology, and even human pathology. (Of course, to achieve this scope and accessibility in such a brief book, Shubin had to forgo much depth and detail; so readers with a background in biology may find it less than elucidating.)
Especially enjoyable are Shubin’s sections on anatomy and fossil hunting, where his passionate prose sometimes verges on the poetic. Discussing the human hand, for instance, he writes: “Our ability to grasp, to build, and to make our thoughts real lies inside this complex of bones, nerves and vessels” (p. 29). He tells of his days as a novice field paleontologist, returning empty-handed day after day while his colleagues returned with copious collections of fossils—and of how, once he finally saw “the distinction between rock and bone” (p. 65), “All of a sudden, the desert floor exploded with bone . . . as if I were wearing a special new pair of glasses” (p. 65).
Although early in the book he says that serendipity is a key factor in successful fossil hunting (p. 5), he later shows other factors to be the true keys to success. Relaying how he chose the field site in his search for the transitional fossil between fish and amphibians, he explains that he chose the site quite intentionally, based on several factors: It contained rocks of the right kind and of the precise age, was little explored, and was little disturbed by human habitation. Once in the field, however, he discovered that the fossils in this location were from deep ocean sediments, not from shallow streams, so he moved to a nearby location. Then he “got lucky.” On his fourth trip to this hand-picked remote area of the Arctic—in his sixth year of hunting—he found the transitional fossil he sought. As Shubin himself puts it, “So much for serendipity” (p. 18). One cannot help but recall Louis Pasteur’s oft-quoted statement that “chance favors the prepared mind”—or, in this case, the prepared and persistent mind.
Although the book is not a polemic against intelligent design, Shubin points out that “not only was the new fish an intermediate between two different kinds of animal, but we had found it also in the right time period in earth’s history and in the right ancient environment”(emphasis original, p. 24). In this context, “the right time period and right environment” means the time and place predicted by evolutionary biology (i.e., just before the first known amphibian fossils and in a shallow, freshwater habitat, as amphibians are descended from freshwater fish). The book also shows quirks and flaws in the “design” of human anatomy; mentions a host of common medical ailments related to our evolutionary history; and explains that our understanding of such things derives from studying not only fish fossils, but also fruit fly genes, reptile jaws, and shark gonads. One lab “used work in flies to find a gene in chickens that tells us about human birth defects. . . . The connections among living creatures run deep” (emphasis original, p. 59). As a paean to the beauty of evolutionary science and the connections between humans and other species, the entire book implicitly dismisses “intelligent design.”
Your Inner Fish is a great introduction to the fact that, as Shubin writes, “We are not separate from the rest of the living world; we are part of it down to our bones” (p. 43).