Originally published 6 November 1989
Stephen Jay Gould has written his best book yet.
Wonderful Life: The Burgess Shale and the Nature of History is the story of some remarkable fossils from the mountains of western Canada, and a sprightlier introduction to the history, methods, and philosophy of science would be hard to imagine. Simply put, Wonderful Life is wonderful — required reading for anyone who wants to understand the nature of science.
But “the nature of history”? Ah, that’s something else. Gould’s ambitious subtitle promises more than the book delivers. Sure enough, he dishes up the Burgess Shale in all its wonderful detail, but the nature of history proves tantalizingly elusive.
The Burgess Shale is a mudstone quarry in the Canadian Rockies that in 1909 yielded a treasure trove of fossils to Charles D. Walcott, head of the Smithsonian Institution and one of the greatest paleontologists of his time. The muds were deposited during the Middle Cambrian period of Earth history, 530 million years ago, near a reef on the floor of an ancient sea. The fossils are preserved with photographic fidelity. They reveal a bizarre zoo of sea-dwelling animals, typically an inch or two long, including five-eyed Opabinia, spike-legged Hallucigenia, and pineapple-shaped Wiwaxia, all now extinct.
Improbable animals
The separate parts of these animals look vaguely familiar, but juggled into wildly improbable combinations, like one of those children’s toys where by turning the segments of a cylinder one creates fantastic animals — a giraffe’s head on a horse’s body with elephant legs. What to make of these “weird wonders,” so unlike anything seen before or since? Walcott found a place for each of the creatures (a couple of dozen altogether) within conventional branches of the tree of life — worms or arthropods. For all their strangeness, Walcott considered all the Burgess animals ancestrally related to present forms of life.
As Gould makes clear, Walcott “shoehorned” the Burgess animals into traditional categories because he was convinced that evolution is a pathway of necessary progress leading from our most primitive ancestor to ourselves, the fittest form of life on Earth and the crown of creation. It didn’t occur to him that the majority of animals in the Burgess sea might be evolutionary dead ends, alternate designs for life that somehow didn’t work out. And that’s where matters stood until the late 1960s when Harry Whittington of Cambridge University decided to take a fresh look at the fossils that had gathered dust for 50 years in laboratory cabinets.
As Whittington and his colleagues Derek Briggs and Simon Conway Morris painstakingly reconstructed the Burgess animals an astonishing truth emerged: Many of these creatures are so fundamentally different from anything alive on Earth today as to require the creation of entirely new phyla (categories) of life — and give a strange new twist to the story of evolution.
Paleontologists have long recognized that something remarkable happened early in the Cambrian period of Earth history, just prior to the deposition of the Burgess Shale. For 3 billion years the Earth had been inhabited only by microscopic, single-celled organisms. Then suddenly there appeared a variety of multi-celled creatures — sponges, trilobites, and jellyfish, for example — including the remote ancestors of all families of life presently on Earth.
Apparently this Cambrian explosion was even more prolific than we had previously imagined. The Burgess Shale contains not only the ancestors of present life, but animals with anatomies wildly different than anything existing today. For a time these improbable Burgess beasts shared the Earth with our more familiar ancestors. Then occurred what Gould calls a “great decimation,” and most of the Burgess animals became extinct. We don’t know the nature of the disaster, or even how quickly it occurred. But never again would life on Earth be so radically diverse.
Contingent on chance?
Now Gould draws his moral: Evolution is a crapshoot. The Burgess fossils give no indication that some of these animals were more or less fit than others. When the great decimation came, survival depended on luck, not fitness or design. Rewind the tape of evolution back to the time of the Burgess Shale, play it again, and no creature remotely like Homo sapiens would be likely to emerge. Concludes Gould: History is contingent — upon a myriad episodes of chance. We are an accidental detail, not the purpose of creation.
I happen to agree with Gould’s conclusion, but I question whether the strict contingency of history is a necessary lesson of the Burgess Shale. Many of us believed that history is modified by chance long before we ever heard of the Burgess dead-end animals. Even Walcott’s traditional tree of life, driven upwards by random mutations acted upon by natural selection (survival of the fittest), gave ample reason to appreciate how forcefully chance sifts and shuffles fate. But surely one can accept contingency without abandoning the idea of an order, or even direction, for evolution.
Contingency, catastrophe, and chaos are currently fashionable in science, but I’ll opt for a healthy dose of good, old-fashioned determinism. If the tape of life were replayed from the time of the Burgess Shale, I would not be surprised if a creature of a certain optimum size, agility, and mobility, with versatile sensory organs and intelligence didn’t again emerge out of the working of Darwinian natural selection, or any other dynamic of evolution that is not pure chance. That creature wouldn’t be us exactly, but an other us, a walking, talking, thinking descendant of unlucky, five-eyed Opabinia, perhaps, or pineapple-shaped Wiwaxia. Not Homo, but certainly sapiens, out there chipping fossils out of the mountain or sitting in Cambridge pondering their meaning.
History is contingent, but it ain’t necessarily a crapshoot. By deifying the roll of the dice Gould out-Walcotts Walcott, who imposed upon the Burgess fossils his own notion of design. Strict contingency, like the idea of fitness, is a matter of faith, informed by experience perhaps, but not a necessary consequence of the Burgess Shale or any other fossils. Gould simply makes his moral too grand for his story. But the story is marvelous, and the moral not absurd.
