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Evolutions That Never Evolved : WONDERFUL LIFE: The Burgess Shale and the Nature of History by Stephen Jay Gould (W. W. Norton: $15.95; 347 pp., illustrated)

October 29, 1989|Allan J. Tobin | Tobin teaches neuroscience and biology at UCLA and is scientific director of the Hereditary Disease Foundation. and

Stephen Jay Gould's new book, "Wonderful Life," recounts two fascinating and previously little-known stories, one about evolution and the other about evolutionary science. The first concerns the relationships between present life on our planet and a set of strange and ancient animals. The second, told as a five-act drama, recounts how three British scientists came to understand these relationships. Gould ranks the work of his paleontological colleagues among the greatest creative achievement of our species, comparable, in his view, to the cave paintings of Lascaux or the cathedral windows of Chartres. Gould goes on to reflect on the importance of contingency in evolutionary history and of concept in evolutionary science.

About 530 million years ago, in an area of ocean about the size of a city block, a mudslide asphyxiated tens of thousands of small marine animals. Most of the trapped organisms lived on the bottom of a shallow sea bed, though others swam or floated above. Their rapid burial insulated them from immediate decay, and their remains became preserved (and chemically transformed) in a rock formation called the Burgess Shale, which now lies high in the Canadian Rockies. The Burgess Shale presents an unequaled snapshot of life in the middle of the Cambrian Period, the earliest span of geological time from which we have abundant fossil evidence of recognizably modern animals.

The discoverer of the Burgess Shale, Charles Doolittle Walcott, was a distinguished leader of the early 20th-Century American scientific establishment. Though his role as secretary of the Smithsonian Institution left him little research time, he interpreted the Burgess animals as primitive members of still-living groups (such as crustaceans, jellyfish and polychaete worms) or of the best-studied group of fossil invertebrates, the trilobites. Walcott thus completely missed the revolutionary significance of his magnificent find.

According to Gould's engaging account, the real meaning of the Burgess animals only began to emerge in the 1970s, when three British paleontologists--Harry Whittington, Derek Briggs, and Simon Conway Morris--undertook to reexamine Burgess fossils, including those originally collected by Walcott. Whittington, Briggs and Conway Morris realized that many Burgess fossils were not merely flat impressions but were three-dimensional relics that they could dissect and inspect, carefully chipping away layers with dental drills. They thus converted the snapshot into a set of stereoscopic images. Their subsequent work, and Gould's book, are attempts to fit these new photographs into a videotape of early animal evolution.

The diversity of anatomical designs among the Burgess animals far exceeds that of all the creatures in all of today's oceans. More baldly stated, the Burgess Shale is full of oddballs: Opabinia, with five eyes, a front-facing nozzle, and a U-shaped gut; Nectocaris, which looks something like a large insect in the front and a fish in the rear; Odontogriphus, a flat animal with both teeth and tentacles; Dinomischus, a sessile animal that resembles a goblet on a long stem; Amiskwia, another swimming animal with tentacles on its head and fins on its sides and tail, and the most peculiar Hallucigenia (see above) , with seven pairs of spines pointing down and seven tentacles pointing up. Altogether, the Burgess animals represent 25 basic body plans, of which only four survive in present-day organisms. The explosion of animal life in the early Cambrian (or Precambrian), then, gave rise to much more than the precursors of modern life. The question, then, is why some forms continued and others perished.

Gould's reflections center around this question. Did the losers disappear because of their inferiority in competition or merely because they had the wrong tickets in a lottery? Could an ancient biologist have predicted which forms would survive and evolve and which would not? Was the evolution of present life, including our own species, in any way be predictable?

Gould's view is embodied in the book's title, borrowed from the Frank Capra film, "It's a Wonderful Life," in which a guardian angel shows a suicidal Jimmy Stewart what his town would have been without his having been there. Gould argues that we cannot ever know what our planet's life would have been like if we replayed history with even minor changes. The present is contingent on what has come before, a statement equally true, according to Gould, of evolutionary history and of history in general.

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