YOUR INNER FISH

How human bones, organs and behavior reveal the history we share with fish, flies, worms and germs.

Shubin (Organismal Biology and Anatomy/Univ. of Chicago) made the front page of the New York Times in 2006 when he discovered a 375-million-year-old fossil fish whose fins contained rudimentary limb bones, perhaps the earliest ancestor of the first creatures that left the sea to live on land. This ancient limb consisted of a single upper bone followed by two lower bones followed by a collection of primitive wrist bones—the same structure, Shubin emphasizes, found today in the limbs of all walking animals, including humans. (It would be a devastating argument against evolution to find a creature with a different pattern of limb bones, but so far that has not happened.) The author traces the history of other body parts—teeth, head, ears, eyes—as far as they go, often billions of years. He also explores how each creature’s DNA assembles a complete individual from a few identical cells. It turns out nature works as economically in embryonic development as it does in evolution. A fish and a human look identical for weeks after fertilization. The segments of DNA that produce proteins to guide the growth of a shark’s fin and a human arm are almost identical, and they go about their work in ways that haven’t changed in 500 million years. Researchers have injected a mouse limb-development protein inside a fish egg to replace the fish equivalent, and the fish grows normal fins. A skillful writer, paleontologist Shubin conveys infectious enthusiasm and illustrates his points with dozens of drawings, sketches, tables and photographs.

Even readers with only a layperson’s knowledge of evolution will learn marvelous things about the unity of all organisms since the beginning of life.