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The Missing Link
A paleontologist argues that your hand was once a fin.

Reviewed by Barbara J. King
Sunday, February 17, 2008

YOUR INNER FISH

A Journey into the 3.5-Billion-Year History Of the Human Body

By Neil Shubin

Pantheon. 229 pp. $24

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. *

Barbara J. King, a professor of biological anthropology at the College of William and Mary, is the author of "Evolving God: A Provocative View on the Origins of Religion."

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