Showdown On The Burgess Shale

Almost a decade ago, Harvard paleontologist and Natural History columnist Stephen Jay Gould published Wonderful Life: The Burgess Shale and the Nature of History (W. W. Norton and Company, 1989). In addition to chronicling ongoing work on the Burgess creatures, Gould used these fascinating fossils to exemplify his view of evolution. A few months ago, in The Crucible of Creation: The Burgess Shale and the Rise of Animals (Oxford University Press, 1998), invertebrate paleontologist Simon Conway Morris, of Cambridge University, a key player in Burgess research, challenged Gould's interpretations. We invited Conway Morris to summarize his argument, which we publish here, along with Gould's reply.

The Challenge

Few books on paleontology have achieved the wide readership of Stephen Jay Gould's Wonderful Life, which popularized research spearheaded by Harry Whittington at Cambridge on the 520-million-year-old Burgess Shale, found between two peaks in the Canadian Rockies near Banff. But Gould did much more than chronicle discoveries concerning these Cambrian fossils; he also set forth his own deeply held views on the mechanisms and nature of evolution--and even on humankind's place in the universe--as the "lessons" to be drawn from the Burgess Shale.

In my new book, The Crucible of Creation, I argue that the major premises and conclusions of Wonderful Life must be seriously challenged. Let me begin with some matters of interpretation of patterns in the fossil record, then move on to paleontological particulars, and finally offer different "lessons" on what the Burgess Shale means in the larger reading of evolutionary history.

Gould emphasizes, above all, the apparent weirdness and diversity of the Burgess fossils. How, he asks, was such an extraordinary range of anatomies produced, and all apparently in a blink of geological time? He hints at a special mechanism at work--some unusual genetic happenstance gone wild--that might account for the production of so many biological novelties in such a startlingly short period of time, perhaps only a few million years. And what if we could "rerun the tape" so that the subsequent history of this maelstrom of diversification would have taken a different course? We would still have a planet full of life, he argues, but surely one utterly different from our familiar world. Notably, this new trajectory of evolution would probably not have led to the human species and its unique form of consciousness and self-awareness, which emerged through a series of contingent accidents in a unique, unrepeatable sequence.

Gould also charges that Charles D. Walcott, the discoverer of the Burgess Shale, was ill equipped to appreciate how diverse these novel phyla of sea creatures really were. Committed to the orthodox view that the range of life-forms must become ever greater over time, Walcott, in Gould's view, was unprepared to confront a world in which the proliferation of different kinds of life-forms (phyla) was much greater in the distant past than in, say, the age of dinosaurs or the more recent age of mammals. Therefore, he argues, Walcott attempted to "shoehorn" a range of previously unknown creatures into a few familiar categories to fit his preconceptions. Gould asserts that paleontologists have only just begun to appreciate the ever-expanding catalog of bizarre "dead-end experiments" conducted by nature in ancient seas.

Looking back at the Cambridge group's classifications of the Burgess Shale, undertaken many decades after Walcott's pioneering work, my colleagues and I can see that we made some mistakes. Too often, we thought we had stumbled across yet another novel body plan (phylum, if you will), and in a few crucial instances, we did not realize that seemingly unrelated fossils were actually fragments of a single organism. With the benefit of hindsight, we can see that we had exaggerated the diversity of these supposedly bizarre fossils and needed to reconsider their evolutionary relationships. Recent discoveries in southern China (Yunnan) and northern Greenland (Peary Land) have provided links that join several of these previously unconnected fossils and establish them in recognizable phyla.

Let's begin with the animal Wiwaxia. In Wonderful Life, it is described as "another Burgess oddball, perhaps closer to the Mollusca than to any other modern phylum ... but probably not very close." Ironically, the first breakthrough in establishing Wiwaxia's affinities came from a postgraduate paleontologist at Harvard who was inspired by Gould's lectures a decade or so ago. This young researcher, Nick Butterfield, managed to extract pieces of scalelike armor from the fossilized creature. When Butterfield studied their microstructure, he noticed immediately that it was the same as that of the chitinous bristles (chaetae) that project from the bodies of such modern annelids as earthworms. His conclusion, published in 1990, was that Wiwaxia was not a mollusk at all but an annelid. Yet this was what Walcott had claimed in 1911. In at least this case, Butterfield concluded, Walcott was not "shoehorning" bizarre animals into familiar phyla, as Gould had charged; Walcott had got it right the first time.