The Universe Within by Neil Shubin Page A

evidence, from the shape and structure of the putative fossils to the chemistry of the rocks that hold them. The hunt is for creatures that not only look like single-celled forms but also reveal the chemical workings of metabolisms.
    With this playbook, Stanley Tyler, Elso Barghoorn, and their scientific descendants exposed the hidden reality inside the rocks: the earliest fossils are now known to be over 3.4 billion years old. Life arose early in the history of our planet and, once off to that start, expanded rapidly to become a menagerie of different kinds ofbacteria, algae, and their relatives.
    Despite their incredible diversity, the organisms that dominated the first billions of years of the history of our planet share one important thing. They are all single celled and microscopic. Some of them lump together to form colonies, but no individual dwelling on Earth for the first 3 billion years was larger than a grain of rice. Big, in the world of living things, had yet to come about.
THROUGH THE LOOKING GLASS

    “That one’s dead,”ThomasBarbour, the director of Harvard’s Museum of Comparative Zoology, shouted while considering a frog lying motionless on the grass in front of him.
    On the roof above Barbour stood his colleague Professor Philip Darlington, holding a bucket of frogs with one hand. With the other, he was pitching the frogs one by one onto the lawn five stories below.
    Barbour nodded as each frog hit and remained motionless in the grass below his feet. When Darlington descended with his empty bucket, he asked Barbour how the animals withstood the impact. Seeing the frogs strewn about, Barbour offered, “All dead.”
    Darlington was a naturalist of the old school: when he wasn’t teaching courses at Harvard College, he was off in the jungle collecting new species, beetles in particular. Tales of his days in the field are legendary, including the time he was grabbed by acrocodile, pulled to the bottom of a stream, and, as the crocodile began to consume him, kicked himself free. Hiking miles to safety with shredded legs and hands, he wrote to his wife later that night only that he had an “episode with a crocodile.”
    In the midst of his explorations in the 1930s, debates were raging about how animals dispersed to new places around the globe. This was the era beforeplate tectonics, and there were two major ways to explainanimal distributions: either there were land bridges between continents—now lost—that allowed animals to walk from place to place, or animals could be blown by wind, water, and storm. Darlington was a firm believer in the latter and his boss, Thomas Barbour, in the former.
    The frog “experiment”—something we would obviously never perform today—began as an argument. During coffee at the museum one afternoon, the two got into a tussle about the theories and made a wager. Barbour held that dispersal by wind was impossible because animals would die upon impact. Darlington countered that wind dispersal would work over considerable distances for small animals. The two agreed on the rooftop test of the theory.
    And what of Darlington’s dead frogs?
    Within minutes after the impact, each frog arose and hopped away. Soon the grass was filled with frogs bounding in different directions. Darlington proved his point.
    Of course, there is nothing unique about frogs that allowed them to survive such a fall; this ability is a reflection of their size. Small animals accelerate more slowly during a fall than do large ones, since they experience more air resistance for a givenmass. In describing this phenomenon,J. B. S. Haldane, one of the founders of evolutionarygenetics, said, “You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away.… A rat is killed, a man is broken, a horse splashes.”
    Let’s say you want topredict what an animal can do—how long it lives, how it moves about—and what it looks like without ever