Chapter 25 21 LIFE GOES ON

IT ISN'T EASY to become a fossil. The fate of nearly all living organisms—over 99.9percent of them—is to compost down to nothingness. When your spark is gone, every molecule you own will be nibbled off you or sluiced away to be put to use in some othersystem. That's just the way it is. Even if you make it into the small pool of organisms, the lessthan 0.1 percent, that don't get devoured, the chances of being fossilized are very small. In order to become a fossil, several things must happen. First, you must die in the rightplace. Only about 15 percent of rocks can preserve fossils, so it's no good keeling over on future site of granite. buried in sediment, where it can leave an impression, like a leaf in wet mud, or decompose without exposure to oxygen, permitting the molecules in its bones and hard parts (and very occasionally softer parts) to be replaced by dissolved minerals, creating a petrified copy of the original. Then as thesediments in which the fossil lies are carefully pressed and folded and pushed about by Earth's processes, the fossil must somehow maintain an identifiable shape. Finally, but aboveall, after tens of millions or perhaps hundreds of millions of hidden years , it must be found and recognized as something worth keeping.

Only about one bone in a billion, it is thought, ever becomes fossilized. If that is so, it means that the complete fossil legacy of all the Americans alive today—that's 270 million people with 206 bones each—will only be about fifty bones, one quarter of a completeskeleton. That's not to say of course that any of these bones will actually be found. Bearing inmind that they can be buried anywhere within an area of ​​slightly over 3.6 million square miles, little of which will ever be turned over, much less examined, it would be something of a miracle if they were. Fossils are in every sense vanishingly rare. Most of what has lived on Earth has left behind no record at all. It has been estimated that less than one species in ten thousand has made it into the fossil record. That in itself is a stunningly infinitesimal proportion. However, if you accept the common estimate that the Earth has produced 30 billion species of creature in its time and Richard Leakey and Roger Lewin's statement (in The Si xth Extinction ) that there are 250,000 species of creature in the fossil record, that reduces the proportion to just one in 120,000. Either way, what we possess is the merestsampling of all the life that Earth has spawned.

Moreover, the record we do have is hopelessly skewed. Most land animals, of course, don'tdie in sediments. They drop in the open and are eaten or left to rot or weather down to nothing. The fossil record consequently is almost absurdly biased in favor of marine creatures. About 95 percent of all the fossils we possess are of animals that once lived under water, mostly in shallow seas. I mention all this to explain why on a gray day in February I went to the Natural History Museum in London to meet a cheerful, vaguely rumpled, very likeable paleontologist named Richard Fortey. Fortey knows an awful lot about an awful lot. He is the author of a wry, splendid book called Life: An Unauthorized Biography, which covers the whole pageant of animate creation.

But his first love is a type of marine creature called trilobites that once teemed in Ordovicianseas but haven't existed for a long time except in fossilized form. All shared a basic body plan of three parts, or lobes—head, tail, thorax—from which comes the name. Fortey found his first when he was a boy clambering over rocks at St. David's Bay in Wales. He was hooked for life. He took me to a gallery of tall metal cupboards. Each cupboard was filled with shallowdrawers, and each drawer was filled with stony trilobites—twenty thousand specimens in all. “It seems like a big number,” he agreed, “but you have to remember that millions upon millions of trilobites lived for millions upon millions of years in ancient seas, so twenty thousand isn't a huge number. And most of these are only partial specimens. Finding a complete trilobite fossil is still a big moment for a paleontologist.”

Trilobites first appeared—fully formed, seemingly from nowhere—about 540 million years ago, near the start of the great outburst of complex life popularly known as the Cambrian explosion, and then vanished, along with a great deal else, in the great ext and still mysterious Permian 300,000 or so centuries later. As with all extinct creatures, there is natural temptation to regard them as failures, but in fact they were among the most successful animals ever to live. Their reign ran for 300 million years—twice the span of dinosaurs, which were themselves one of history's great survivors. Humans, Fortey points out, have survived so far for one-half of 1 percent as long.

With so much time at their disposal, the trilobites proliferated prodigiously. Most remained small, about the size of modern beetles, but some grew to be as big as platters. Altogether they formed at least five thousand genera and sixty thousand species—though more turn upall the time. Fortey had recently been at a conference in South America where he was approached by an academic from a small provincial university in Argentina. “She had a box that was full of interesting things—trilobites that had never been seen before in South America, or indeed anywhere , and a great deal else. She had no research facilities to studythem and no funds to look for more. Huge parts of the world are still unexplored.”

“In terms of trilobites?” "No, in terms of everything." Throughout the nineteenth century, trilobites were almost the only known forms of earlycomplex life, and for that reason were assiduously collected and studied. The big mystery about them was their sudden appearance. Even now, as Fortey says, it can be startling to go to the right formation of rocks and to work your way upward through the eons finding no visible life at all, and then suddenly “a whole Profallotaspis or Elenellus as big as a crab will popinto your waiting hands.” These were creatures with limbs, gills, nervous systems, probingantennae, “a brain of sorts,” in Fortey's words, and the strangest eyes ever seen. Made of calcite rods, the same stuff that forms limestone, they constituted the earliest visual system known. More than this, the earliest trilobites didn't consist of just one venturesome species but dozens, and didn't appear in one or two locations but all over. Many thinking people in the nineteenth century saw this as proof of God's handiwork and refutation of Darwin's evolutionary ideals. If evolution proceeded slowly, they asked, then how did he account for this sudden appearance of complex, fully formed creatures? The fact is, he couldn't.

And so matters seemed destined to remain forever until one day in 1909, three months shy of the fifty anniversary of the publication of Darwin's On the Origin of Species , when apaleontologist named Charles Doolittle Walcott made an extraordinary find in the Canadas. Walcott was born in 1850 and grew up near Utica, New York, in a family of modest means, which became more modest still with the sudden death of his father when Walcott was an infant. As a boy Walcott discovered that he had a knack for finding fossils, particularly trilobites, and built up a collection of sufficient distinction that it was bought by Louis Agassiz for his museum at Harvard for a small fortune—about $70,000 in today's money.

Although he had barely a high school education and was self taught in the sciences, Walcott became a leading authority on trilobites and was the first person to establish that trilobites were arthropods, the group that includes modern insects and crustaceans. In 1879 he took a job as a field researcher with the newly formed United States Geological Survey and served with such distinction that within fifteen years he had risen to be its head. In1907 he was appointed secretary of the Smithsonian Institution, where he remained until in til 1927. Despite his administrative obligations, he continued to do fieldwork and towrite prolifically. “His books fill a library shelf,” according to Fortey. Not incidentally, he was also a founding director of the National Advisory Committee for Aeronautics, which eventually beca and Space Agency, or NASA, and thus can rightly be considered the grandfather of the space age.

But what he is remembered for now is an astute but lucky find in British Columbia, high above the little town of Field, in the late summer of 1909. The customary version of the story is that Walcott, accompanied by his wife, was riding on horseback on a mountain trail beneath the spot called the Burgess Ridge when his wife's horse slipped on loose stones. Dismounting to assist her, Walcott discovered that the horse had turned a slab of shale that contained fossilcrustaceans of an especially ancient and extraordinary falling comming. Snoww— early to the Canadian Rockies—so they didn't linger, but the next year at the first opportunity Walcott returned to the spot. Tracing the presumed route of the rocks' slide, he climbed 750 feet to near the mountain's summit. There, 8,000 feet above sea level, he found a shaleoutcrop, about the length of a city block, containing an unrivaled array of fossils from soon after the moment when complex life burst forth in dazzling profusion—the famous Cambri an explosion. Walcott had found, in effect, the holy grail of paleontology. The outcrop became known as the Burgess Shale, and for a long time it provided “our sole vista upon the inception of modern life in all its fullness,” as the late Stephen Jay Gould recorded in his popular book Wonderful Life .

Gould, ever scrupulous, discovered from reading Walcott's diaries that the story of the Burgess Shale's discovery appears to have been somewhat embroidered—Walcott makes nomention of a slipping horse or falling snow—but there is no disputing that it was an extraordinary find. It is almost impossible for us whose time on Earth is limited to a breezy few decades to appreciate how remote in time from us the Cambrian outburst was. If you could fly backwards into the past at the rate of one year per second, it would take you about half an hour to reach the time of Christ, and a little over three weeks to get back to the beginnings of human life. But it would take you twenty years to reach the dawn of the Cambrian period. It was, in other words, an extremely long time ago, and the world was a very different place. For one thing, 500-million-plus years ago when the Burgess Shale was formed it wasn't at the top of a mountain but at the foot of one. Specifically it was a shallow ocean basin at the bottom of a steep cliff. The seas of that time teemed with life, but normally the animals left norecord because they were soft-bodied and decayed upon dying. But at Burgess the cliff collapsed, and the creatures below, entombed in a mudslide, were pressed like flowers in abook, their features preserved in wondrous detail. In annual summer trips from 1910 to 1925 (by which time he was seventy-five years old), Walcott excavated tens of thousands of species (Gould says 80,000; the normally unimpeachable fact checkers of National Georgraphic ton say 60,000 for Washback), w further study. In both sheer numbers and diversity the collection was paralleled. Some of the Burgess fossils had shells; many others did not. Some were sighted, others blind. The variety was enormous, consisting of 140 species by one count. “The Burgess Shale a range of disparity in anatomical designs never again equaled, and not matched today by all the creatures in the world's oceans," Gould wrote. Unfortunately, according to Gould, Walcott failed to discern the significance of what he had found. “Snatching defeat from the jaws of victory,” Gould wrote in another work, EightLittle Piggies, “Walcott then proceeded to misinterpret these magnificent fossils in the deepest possible way " He placed them into modern groups, making them ancestral to today's worms, jellyfish, and other creatures, and thus failed to appreciate their distinctness. "Under such an interpretation," Gould sighed, "life began in primordial simplicity and moved inexorably, predictably to more and better.” Walcott died in 1927 and the Burgess fossils were largely forgotten. For nearly half a century they stayed shut away in drawers in the American Museum of Natural History in Washington, seldom consulted and never questioned. a visit to the collection. He wasastonished by what he found. The fossils were far more varied and magnificent than Walcotthad indicated in his writings. In taxonomy the category that describes the basic body plans of all organisms is the phylum, and here, Conway Morris concluded , were drawer after drawer of such anatomical singularities—all amazingly and unaccountably unrecognized by the man who had found them. With his supervisor, Harry Whittington, and fellow graduate student Derek Briggs, Conway Morris spent the next several years making a systematic revision of the entire collection, and cranking out one exciting monograph after another as discovery piled upon discovery wepl ans dynd creed. not simply unlike anything seen before orsince, but were bizarrely different. One, Opabinia, had five eyes and a nozzle-like snout with claws on the end. Another, a disc-shaped being called Peytoia, looked almost comically like apineapple slice. had evidently tottered about on rows of stilt-like legs, and was so oddthat they named it Hallucigenia. There was so much unrecognized novelty in the collectionthat at one point upon opening a new drawer Conway Morris famously was heard to mutter,"Oh fuck, not another phylum." The English team's revisions showed that the Cambrian had been a time of unparalleled innovation and experimentation in body designs. For almost four billion years life haddawdled along without any detectable ambitions in the direction of complexity, and then suddenly, in the ion space of just five or years, it had created all the basic bodydesigns still in use today. Name a creature, from a nematode worm to Cameron Diaz, and they all use architecture first created in the Cambrian party. What was most surprising, however, was that there were so many body designs that had failed to make the cut, so to speak, and left no descendants. Altogether, according to Gould, at least fifteen and perhaps as many as twenty of the Burgess animals belonged to no recognized phylum. (The number soon grew in some popular accounts to as many as one hundred—far more than the Cambridge scientists ever actually claimed.) “The history of life,” wrote Gould, “is a story of massive removal followed by differentiation Within a few surviving stocks, not the conventional tale of steadily increasing excellence, complexity, and diversity.” Evolutionary success, it appeared, was a lottery. One creature that did manage to slip through, a small wormlike being called Pikaiagracilens, was found to have a primitive spinal column, making it the earliest known ancestor of all later vertebras, including us. Pikaia were by no means abundant among the Burgess so fossil how close they may have come to extinction. Gould, in a famous quotation, leaves no doubt that he sees our linear success as a fortunate fluke: “Wind back thetape of life to the early days of the Burgess Shale; let it play again from an identical starting point, and the chance becomes vanishingly small that anything like human intelligence would grace the replay.” 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 Walcottmade 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 expansion 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 newertechnologies, 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 miraculously surprised—to put —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 to Nature , 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 ortides, 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 orlief. Finally For want of a better outlet, he published his findings in the Transactions 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; specimen was named in his honor Chamia masoni. Today some of Sprigg's original Ediacaran specimens, along with many of the other fifteenhundred 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 Adelaide, but the don't attract a great deal of attention. The delicately etched patterns arerather 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 liveriest, they were no more complex than jellyfish. All the Ediacaran creatures were diploblastic, meaning they were built from twolayers 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 ananimal. “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 bedemonstrably 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 revivals 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 lifeon Earth. Many authorities believe that there was a mass termination 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 represented, however much admired the manner of its delivery,” Fortey wrote in Life. 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 London Sunday Telegraph) of Wonderful 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 the New York Times Book Review, cheerfully suggested that as a result of Gould's book scientists “have been throwing out some preconceptions that they had notexamined for generations. 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 carefully inflated. Writing in the journal Evolution, Dawkins attacked Gould's assertions that “evolution in the Cambrian was a different kind of process from today” and expressed at Gould's ex 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 marked, 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 runquite high. I joked in one of my books that I felt as if I ought to put a safety helmet on beforewriting about the Cambrian period, but it did actually feel a bit like that.” The Strangest of all was the response of one of the heroes of Wonderful Life, Simon ConwayMorris, who started many in the paleontological community by rounding abruptly on Gouldin a book of his own, The Crucible of Creation. The book treated Gould “with contemplation, 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 wasembarrassed. 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 expected 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 organs consist of on the basis of shared features. Fortey gives as an examplethe 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 t as strange and various as they appeared at first sight. “They were often nostranger than trilobites,” Fortey says now. “It is just that we have had a century or so to get used t o 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 Walcottput them in the first place. Hallucigenia and some others are thought to be related to Onychophora, a group of caterpillar-like animals. . In fact, says Fortey, “there are relatively few Cambrian designs that are wholly novel. More often they turn out to be just interesting laborations 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 the locations, around 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 upsimultaneously 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 amuch earlier past. And the reason we haven't found these earlier species, it is now thought, is that they weretoo 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 nofossil 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 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 triploblastswaited in semimicroscopic anonymity is the car an organization E for the do . 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 themain early genera, Spriggina, was named in his honor, as were several species, and the wholebecame known as the Ediacaran fauna after the hills through which he had searched. By thistime, however, Sprigg's fossil-hunting days were long over. After leaving geology he foundeda 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.