Our fishy selves

Paleontologists are romantic figures in our culture, and perhaps they are more likely than most of us to be romantics at heart. In Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body, paleontologist Neil Shubin mixes logic, enthusiasm and various personal anecdotes to draw the reader into his world.

In 2004, Shubin was part of a team that announced the discovery of a fossil thought to represent a missing link between fish and limbed, landlubbing animals—a fin-limbed creature they called Tiktaalik. It was a dramatic find, but Shubin argues it’s only one of many that establishes the evolutionary lineage from the first life forms to humans.

The first part of Your Inner Fish gives a brief, logical answer to a question that might not be immediately obvious: Of all the rocks on Earth, how do paleontologists know which ones are likely to contain fossils? To a certain extent, it’s luck, but geology-based logic can be used to predict likely places to search for fossil-embedded rocks. Far from being a random assortment of bones and footprints, fossil beds are laid down with a certain order. This order is sometimes upset. When that happens, fossils can end up in unexpected places. For example, fish don’t swim in lava, but Shubin’s team once found fish fossils among rocks formed from lava.

But what good are fossils, anyway? Shubin’s central point is that we can learn about ourselves in the present—and about how we got here—by understanding the fossil record. Fossil animals (and for the most part, Shubin deals with animals rather than plants, though microbes enjoy a substantial part in his narrative, too) are found in rock layers that are the same age as the animals. Older layers often lie deeper than younger layers.

To illustrate what fossils can tell us, Shubin invites the reader to take an imaginary stroll through the zoo. Divide the animals into a few basic categories: All animals in his zoo have heads, some have limbs and heads and fewer still have hair and breasts as well as heads and limbs. The last category is mammals, and Shubin points out that mammalian fossils are more recent than the earliest fossils of fish, which are the first animals with heads to appear in the fossil record. These early animals are related to us through shared ancestors that are in some cases unthinkably distant. Shubin refers to most known fossils as “cousins” of our ancestors.

More recent fossils incorporate characteristics that we can recognize as our own—not only limbs, but eyes, ears and noses. Inner Fish briefly covers what’s known about the evolution of each of these. Also, just as scientists examine bones, they can examine genes of fish, reptiles and mammals (and even insects and bacteria) to figure out why our bodies work the way they do.

After drawing connections between all sorts of life forms, Shubin then uses the connections to speculate on possible explanations for a few mysteries about us and our jerry-rigged bodies, which were not designed to do what we need them to. These mysteries range from obesity and diabetes to why drunks get the spins and why we can blame tadpoles every time we get hiccups. Whether these explanations are ultimately supported scientifically, for now, they are emotionally satisfying.

With an abundance of helpful illustrations and straightforward text, the explanatory framework used by Shubin is very effective, even for readers with little science background. An excellent instructor, it’s clear Shubin loves his subject.