Gould’s book was published in 1989 to general critical acclaim and was a great commercial success. What wasn’t generally known was that many scientists didn’t agree with Gould’s conclusions at all, and that it was all soon to get very ugly. In the context of the Cambrian, “explosion” would soon have more to do with modern tempers than ancient physiological facts.

In fact, we now know, complex organisms existed at least a hundred million years before the Cambrian. We should have known a whole lot sooner. Nearly forty years after Walcott made his discovery in Canada, on the other side of the planet in Australia, a young geologist named Reginald Sprigg found something even older and in its way just as remarkable.

In 1946 Sprigg was a young assistant government geologist for the state of South Australia when he was sent to make a survey of abandoned mines in the Ediacaran Hills of the Flinders Range, an expanse of baking outback some three hundred miles north of Adelaide. The idea was to see if there were any old mines that might be profitably reworked using newer technologies, so he wasn’t studying surface rocks at all, still less fossils. But one day while eating his lunch, Sprigg idly overturned a hunk of sandstone and was surprised—to put it mildly—to see that the rock’s surface was covered in delicate fossils, rather like the impressions leaves make in mud. These rocks predated the Cambrian explosion. He was looking at the dawn of visible life.

Sprigg submitted a paper toNature , but it was turned down. He read it instead at the next annual meeting of the Australian and New Zealand Association for the Advancement of Science, but it failed to find favor with the association’s head, who said the Ediacaran imprints were merely “fortuitous inorganic markings”—patterns made by wind or rain or tides, but not living beings. His hopes not yet entirely crushed, Sprigg traveled to London and presented his findings to the 1948 International Geological Congress, but failed to excite either interest or belief. Finally, for want of a better outlet, he published his findings in theTransactions of the Royal Society of South Australia . Then he quit his government job and took up oil exploration.

Nine years later, in 1957, a schoolboy named John Mason, while walking through Charnwood Forest in the English Midlands, found a rock with a strange fossil in it, similar to a modern sea pen and exactly like some of the specimens Sprigg had found and been trying to tell everyone about ever since. The schoolboy turned it in to a paleontologist at the University of Leicester, who identified it at once as Precambrian. Young Mason got his picture in the papers and was treated as a precocious hero; he still is in many books. The specimen was named in his honorChamia masoni .

Today some of Sprigg’s original Ediacaran specimens, along with many of the other fifteen hundred specimens that have been found throughout the Flinders Range since that time, can be seen in a glass case in an upstairs room of the stout and lovely South Australian Museum in Adelaide, but they don’t attract a great deal of attention. The delicately etched patterns are rather faint and not terribly arresting to the untrained eye. They are mostly small and disc-shaped, with occasional, vague trailing ribbons. Fortey has described them as “soft-bodied oddities.”

There is still very little agreement about what these things were or how they lived. They had, as far as can be told, no mouth or anus with which to take in and discharge digestive materials, and no internal organs with which to process them along the way. “In life,” Fortey says, “most of them probably simply lay upon the surface of the sandy sediment, like soft, structureless and inanimate flatfish.” At their liveliest, they were no more complex than jellyfish. All the Ediacaran creatures were diploblastic, meaning they were built from two layers of tissue. With the exception of jellyfish, all animals today are triploblastic.

Some experts think they weren’t animals at all, but more like plants or fungi. The distinctions between plant and animal are not always clear even now. The modern sponge spends its life fixed to a single spot and has no eyes or brain or beating heart, and yet is an animal. “When we go back to the Precambrian the differences between plants and animals were probably even less clear,” says Fortey. “There isn’t any rule that says you have to be demonstrably one or the other.”

Nor is it agreed that the Ediacaran organisms are in any way ancestral to anything alive today (except possibly some jellyfish). Many authorities see them as a kind of failed experiment, a stab at complexity that didn’t take, possibly because the sluggish Ediacaran organisms were devoured or outcompeted by the lither and more sophisticated animals of the Cambrian period.

“There is nothing closely similar alive today,” Fortey has written. “They are difficult to interpret as any kind of ancestors of what was to follow.”

The feeling was that ultimately they weren’t terribly important to the development of life on Earth. Many authorities believe that there was a mass extermination at the Precambrian–Cambrian boundary and that all the Ediacaran creatures (except the uncertain jellyfish) failed to move on to the next phase. The real business of complex life, in other words, started with the Cambrian explosion. That’s how Gould saw it in any case.

As for the revisions of the Burgess Shale fossils, almost at once people began to question the interpretations and, in particular, Gould’s interpretation of the interpretations. “From the first there were a number of scientists who doubted the account that Steve Gould had presented, however much they admired the manner of its delivery,” Fortey wrote inLife . That is putting it mildly.

“If only Stephen Gould could think as clearly as he writes!” barked the Oxford academic Richard Dawkins in the opening line of a review (in the LondonSunday Telegraph ) ofWonderful Life . Dawkins acknowledged that the book was “unputdownable” and a “literary tour-de-force,” but accused Gould of engaging in a “grandiloquent and near-disingenuous” misrepresentation of the facts by suggesting that the Burgess revisions had stunned the paleontological community. “The view that he is attacking—that evolution marches inexorably toward a pinnacle such as man—has not been believed for 50 years,” Dawkins fumed.

And yet that was exactly the conclusion to which many general reviewers were drawn. One, writing in theNew York Times Book Review , cheerfully suggested that as a result of Gould’s book scientists “have been throwing out some preconceptions that they had not examined for generations. They are, reluctantly or enthusiastically, accepting the idea that humans are as much an accident of nature as a product of orderly development.”

But the real heat directed at Gould arose from the belief that many of his conclusions were simply mistaken or carelessly inflated. Writing in the journalEvolution , Dawkins attacked Gould’s assertions that “evolution in the Cambrian was a differentkind of process from today” and expressed exasperation at Gould’s repeated suggestions that “the Cambrian was a period of evolutionary ‘experiment,’ evolutionary ‘trial and error,’ evolutionary ‘false starts.’ . . . It was the fertile time when all the great ‘fundamental body plans’ were invented. Nowadays, evolution just tinkers with old body plans. Back in the Cambrian, new phyla and new classes arose. Nowadays we only get new species!”

Noting how often this idea—that there are no new body plans—is picked up, Dawkins says: “It is as though a gardener looked at an oak tree and remarked, wonderingly: ‘Isn’t it strange that no major new boughs have appeared on this tree for many years? These days, all the new growth appears to be at the twig level.’ ”

“It was a strange time,” Fortey says now, “especially when you reflected that this was all about something that happened five hundred million years ago, but feelings really did run quite high. I joked in one of my books that I felt as if I ought to put a safety helmet on before writing about the Cambrian period, but it did actually feel a bit like that.”

Strangest of all was the response of one of the heroes ofWonderful Life , Simon Conway Morris, who startled many in the paleontological community by rounding abruptly on Gould in a book of his own,The Crucible of Creation . The book treated Gould “with contempt, even loathing,” in Fortey’s words. “I have never encountered such spleen in a book by a professional,” Fortey wrote later. “The casual reader ofThe Crucible of Creation , unaware of the history, would never gather that the author’s views had once been close to (if not actually shared with) Gould’s.”

When I asked Fortey about it, he said: “Well, it was very strange, quite shocking really, because Gould’s portrayal of him had been so flattering. I could only assume that Simon was embarrassed. You know, science changes but books are permanent, and I suppose he regretted being so irremediably associated with views that he no longer altogether held. There was all that stuff about ‘oh fuck, another phylum’ and I expect he regretted being famous for that.”

What happened was that the early Cambrian fossils began to undergo a period of critical reappraisal. Fortey and Derek Briggs—one of the other principals in Gould’s book—used a method known as cladistics to compare the various Burgess fossils. In simple terms, cladistics consists of organizing organisms on the basis of shared features. Fortey gives as an example the idea of comparing a shrew and an elephant. If you considered the elephant’s large size and striking trunk you might conclude that it could have little in common with a tiny, sniffing shrew. But if you compared both of them with a lizard, you would see that the elephant and shrew were in fact built to much the same plan. In essence, what Fortey is saying is that Gould saw elephants and shrews where they saw mammals. The Burgess creatures, they believed, weren’t as strange and various as they appeared at first sight. “They were often no stranger than trilobites,” Fortey says now. “It is just that we have had a century or so to get used to trilobites. Familiarity, you know, breeds familiarity.”

This wasn’t, I should note, because of sloppiness or inattention. Interpreting the forms and relationships of ancient animals on the basis of often distorted and fragmentary evidence is clearly a tricky business. Edward O. Wilson has noted that if you took selected species of modern insects and presented them as Burgess-style fossils nobody would ever guess that they were all from the same phylum, so different are their body plans. Also instrumental in helping revisions were the discoveries of two further early Cambrian sites, one in Greenland and one in China, plus more scattered finds, which between them yielded many additional and often better specimens.

The upshot is that the Burgess fossils were found to be not so different after all.Hallucigenia , it turned out, had been reconstructed upside down. Its stilt-like legs were actually spikes along its back.Peytoia , the weird creature that looked like a pineapple slice, was found to be not a distinct creature but merely part of a larger animal calledAnomalocaris . Many of the Burgess specimens have now been assigned to living phyla—just where Walcott put them in the first place.Hallucigenia and some others are thought to be related toOnychophora, a group of caterpillar-like animals. Others have been reclassified as precursors of the modern annelids. In fact, says Fortey, “there are relatively few Cambrian designs that are wholly novel. More often they turn out to be just interesting elaborations of well-established designs.” As he wrote in his bookLife : “None was as strange as a present day barnacle, nor as grotesque as a queen termite.”

So the Burgess Shale specimens weren’t so spectacular after all. This made them, as Fortey has written, “no less interesting, or odd, just more explicable.” Their weird body plans were just a kind of youthful exuberance—the evolutionary equivalent, as it were, of spiked hair and tongue studs. Eventually the forms settled into a staid and stable middle age.

But that still left the enduring question of where all these animals had come from—how they had suddenly appeared from out of nowhere.

Alas, it turns out the Cambrian explosion may not have been quite so explosive as all that. The Cambrian animals, it is now thought, were probably there all along, but were just too small to see. Once again it was trilobites that provided the clue—in particular that seemingly mystifying appearance of different types of trilobite in widely scattered locations around the globe, all at more or less the same time.

On the face of it, the sudden appearance of lots of fully formed but varied creatures would seem to enhance the miraculousness of the Cambrian outburst, but in fact it did the opposite. It is one thing to have one well-formed creature like a trilobite burst forth in isolation—that really is a wonder—but to have many of them, all distinct but clearly related, turning up simultaneously in the fossil record in places as far apart as China and New York clearly suggests that we are missing a big part of their history. There could be no stronger evidence that they simply had to have a forebear—some grandfather species that started the line in a much earlier past.

And the reason we haven’t found these earlier species, it is now thought, is that they were too tiny to be preserved. Says Fortey: “It isn’t necessary to be big to be a perfectly functioning, complex organism. The sea swarms with tiny arthropods today that have left no fossil record.” He cites the little copepod, which numbers in the trillions in modern seas and clusters in shoals large enough to turn vast areas of the ocean black, and yet our total knowledge of its ancestry is a single specimen found in the body of an ancient fossilized fish.

“The Cambrian explosion, if that’s the word for it, probably was more an increase in size than a sudden appearance of new body types,” Fortey says. “And it could have happened quite swiftly, so in that sense I suppose it was an explosion.” The idea is that just as mammals bided their time for a hundred million years until the dinosaurs cleared off and then seemingly burst forth in profusion all over the planet, so too perhaps the arthropods and other triploblasts waited in semimicroscopic anonymity for the dominant Ediacaran organisms to have their day. Says Fortey: “We know that mammals increased in size quite dramatically after the dinosaurs went—though when I say quite abruptly I of course mean it in a geological sense. We’re still talking millions of years.”

Incidentally, Reginald Sprigg did eventually get a measure of overdue credit. One of the main early genera,Spriggina , was named in his honor, as were several species, and the whole became known as the Ediacaran fauna after the hills through which he had searched. By this time, however, Sprigg’s fossil-hunting days were long over. After leaving geology he founded a successful oil company and eventually retired to an estate in his beloved Flinders Range, where he created a wildlife reserve. He died in 1994 a rich man.