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Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body

In Your Inner Fish, Neil Shubin tells the story of evolution by tracing the organs of the human body back millions of years, long before the first creatures walked the earth. By examining fossils and DNA, Shubin shows us that our hands actually resemble fish fins, our head is organized like that of a long-extinct jawless fish, and major parts of our genome look and function like those of worms and bacteria.

The beginning  of Your Inner Fish deals with Shubin’s search for a fossil of a creature that The Theory of Evolution by Natural Selection said must exist but had yet to be found.

An intermediate stage between fish and reptile had long been hypothesized to have existed during the Late Devonian, some 375 million years ago. Sure enough, in some exposed rocks from the Late Devonian, Shubin’s team discovered something positively astounding. A fish with wrists.

Shubin, a paleontologist and professor of anatomy at the University of Chicago, made the astounding discovery of Tiktaalik, in the Canadian Arctic in 2004.  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.”

Tiktaalik, like all fossils, has an interesting story to tell. In this case, it’s the story of how human beings are put together. Shubin explains how the development of Tiktaalik’s wrists as analogous to the single upper arm bone, two bone forearm, many boned wrist structure found in every mammal’s anatomy. Further, he shows how the fin structures of fish like Tiktaalik hold the blue print for the mammalian paw and the opposable thumb structures in the hands of primates.

The way Shubin melds the data of fossils and genetics is very clever, 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 without thinking about shared evolution.

Quite worrisome is Shubin’s tendency to oversell the relationship of fish and humans. Our 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.

Overall this book was a total joy to read and I would heartily recommend it to anyone.

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3 Responses

  1. I read this book a year or so ago. Shubin explains things clearly and the book is very readable. I agree with your assessment that, at this stage in our development, we probably should pay more attention to our inner apes than our inner fishes. Still, the fish connections are fascinating to ponder.

  2. Well, I got here late but I am absolutely facinated! I had intended to ask you for a recommendation on evolution so reading this post is quite timely. I am ordering the book now.

    • Two more awesome ones are Evolution: The First Four Billion Years edited by Michael Ruse and Evolution: What The Fossils Say And Why It Matters. And of course you have Jerry Coyne’s Why Evolution Is True and Dawkins The Greatest Show On Earth.

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