A short history of nearly everything

‘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 of Wonderful 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 of The 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 called Anomalocaris. 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 to Onychophora, 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 book Life: “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.

22 GOOD-BYE TO ALL THAT

WHEN YOU CONSIDER it from a human perspective, and clearly it would be difficult for us to do otherwise, life is an odd thing. It couldn’t wait to get going, but then, having gotten going, it seemed in very little hurry to move on.

Consider the lichen. Lichens are just about the hardiest visible organisms on Earth, but among the least ambitious. They will grow happily enough in a sunny churchyard, but they particularly thrive in environments where no other organism would go-on blowy mountaintops and arctic wastes, wherever there is little but rock and rain and cold, and almost no competition. In areas of Antarctica where virtually nothing else will grow, you can find vast expanses of lichen-four hundred types of them-adhering devotedly to every wind-whipped rock.

For a long time, people couldn’t understand how they did it. Because lichens grew on bare rock without evident nourishment or the production of seeds, many people-educated people-believed they were stones caught in the process of becoming plants. “Spontaneously, inorganic stone becomes living plant!” rejoiced one observer, a Dr. Homschuch, in 1819.