A short history of nearly everything (48 page)

In the seas it was much the same story. All the ammonites vanished, but their cousins the nautiloids, who lived similar lifestyles, swam on. Among plankton, some species were practically wiped out—92 percent of foraminiferans, for instance—while other organisms like diatoms, designed to a similar plan and living alongside, were comparatively unscathed.

These are difficult inconsistencies. As Richard Fortey observes: “Somehow it does not seem satisfying just to call them ‘lucky ones’ and leave it at that.” If, as seems entirely likely, the event was followed by months of dark and choking smoke, then many of the insect survivors become difficult to account for. “Some insects, like beetles,” Fortey notes, “could live on wood or other things lying around. But what about those like bees that navigate by sunlight and need pollen? Explaining their survival isn’t so easy.”

Above all, there are the corals. Corals require algae to survive and algae require sunlight, and both together require steady minimum temperatures. Much publicity has been given in the last few years to corals dying from changes in sea temperature of only a degree or so. If they are that vulnerable to small changes, how did they survive the long impact winter?

There are also many hard-to-explain regional variations. Extinctions seem to have been far less severe in the southern hemisphere than the northern. New Zealand in particular appears to have come through largely unscathed even though it had almost no burrowing creatures. Even its vegetation was overwhelmingly spared, and yet the scale of conflagration elsewhere suggests that devastation was global. In short, there is just a great deal we don’t know.

Some animals absolutely prospered—including, a little surprisingly, the turtles once again. As Flannery notes, the period immediately after the dinosaur extinction could well be known as the Age of Turtles. Sixteen species survived in North America and three more came into existence soon after.

Clearly it helped to be at home in water. The KT impact wiped out almost 90 percent of land-based species but only 10 percent of those living in fresh water. Water obviously offered protection against heat and flame, but also presumably provided more sustenance in the lean period that followed. All the land-based animals that survived had a habit of retreating to a safer environment during times of danger—into water or underground—either of which would have provided considerable shelter against the ravages without. Animals that scavenged for a living would also have enjoyed an advantage. Lizards were, and are, largely impervious to the bacteria in rotting carcasses. Indeed, often they are positively drawn to it, and for a long while there were clearly a lot of putrid carcasses about.

It is often wrongly stated that only small animals survived the KT event. In fact, among the survivors were crocodiles, which were not just large but three times larger than they are today. But on the whole, it is true, most of the survivors were small and furtive. Indeed, with the world dark and hostile, it was a perfect time to be small, warm-blooded, nocturnal, flexible in diet, and cautious by nature—the very qualities that distinguished our mammalian forebears. Had our evolution been more advanced, we would probably have been wiped out. Instead, mammals found themselves in a world to which they were as well suited as anything alive.

However, it wasn’t as if mammals swarmed forward to fill every niche. “Evolution may abhor a vacuum,” wrote the paleobiologist Steven M. Stanley, “but it often takes a long time to fill it.” For perhaps as many as ten million years mammals remained cautiously small. In the early Tertiary, if you were the size of a bobcat you could be king.

But once they got going, mammals expanded prodigiously—sometimes to an almost preposterous degree. For a time, there were guinea pigs the size of rhinos and rhinos the size of a two-story house. Wherever there was a vacancy in the predatory chain, mammals rose (often literally) to fill it. Early members of the raccoon family migrated to South America, discovered a vacancy, and evolved into creatures the size and ferocity of bears. Birds, too, prospered disproportionately. For millions of years, a gigantic, flightless, carnivorous bird called Titanis was possibly the most ferocious creature in North America. Certainly it was the most daunting bird that ever lived. It stood ten feet high, weighed over eight hundred pounds, and had a beak that could tear the head off pretty much anything that irked it. Its family survived in formidable fashion for fifty million years, yet until a skeleton was discovered in Florida in 1963, we had no idea that it had ever existed.

Which brings us to another reason for our uncertainty about extinctions: the paltriness of the fossil record. We have touched already on the unlikelihood of any set of bones becoming fossilized, but the record is actually worse than you might think. Consider dinosaurs. Museums give the impression that we have a global abundance of dinosaur fossils. In fact, overwhelmingly museum displays are artificial. The giant Diplodocus that dominates the entrance hall of the Natural History Museum in London and has delighted and informed generations of visitors is made of plaster—built in 1903 in Pittsburgh and presented to the museum by Andrew Carnegie. The entrance hall of the American Museum of Natural History in New York is dominated by an even grander tableau: a skeleton of a large Barosaurus defending her baby from attack by a darting and toothy Allosaurus. It is a wonderfully impressive display—the Barosaurus rises perhaps thirty feet toward the high ceiling—but also entirely fake. Every one of the several hundred bones in the display is a cast. Visit almost any large natural history museum in the world—in Paris, Vienna, Frankfurt, Buenos Aires, Mexico City—and what will greet you are antique models, not ancient bones.

The fact is, we don’t really know a great deal about the dinosaurs. For the whole of the Age of Dinosaurs, fewer than a thousand species have been identified (almost half of them known from a single specimen), which is about a quarter of the number of mammal species alive now. Dinosaurs, bear in mind, ruled the Earth for roughly three times as long as mammals have, so either dinosaurs were remarkably unproductive of species or we have barely scratched the surface (to use an irresistibly apt cliché).

For millions of years through the Age of Dinosaurs not a single fossil has yet been found. Even for the period of the late Cretaceous—the most studied prehistoric period there is, thanks to our long interest in dinosaurs and their extinction—some three quarters of all species that lived may yet be undiscovered. Animals bulkier than the Diplodocus or more forbidding than tyrannosaurus may have roamed the Earth in the thousands, and we may never know it. Until very recently everything known about the dinosaurs of this period came from only about three hundred specimens representing just sixteen species. The scantiness of the record led to the widespread belief that dinosaurs were on their way out already when the KT impact occurred.

In the late 1980s a paleontologist from the Milwaukee Public Museum, Peter Sheehan, decided to conduct an experiment. Using two hundred volunteers, he made a painstaking census of a well-defined, but also well-picked-over, area of the famous Hell Creek formation in Montana. Sifting meticulously, the volunteers collected every last tooth and vertebra and chip of bone—everything that had been overlooked by previous diggers. The work took three years. When finished they found that they had more than tripled the global total of dinosaur fossils from the late Cretaceous. The survey established that dinosaurs remained numerous right up to the time of the KT impact. “There is no reason to believe that the dinosaurs were dying out gradually during the last three million years of the Cretaceous,” Sheehan reported.

We are so used to the notion of our own inevitability as life’s dominant species that it is hard to grasp that we are here only because of timely extraterrestrial bangs and other random flukes. The one thing we have in common with all other living things is that for nearly four billion years our ancestors have managed to slip through a series of closing doors every time we needed them to. Stephen Jay Gould expressed it succinctly in a well-known line: “Humans are here today because our particular line never fractured—never once at any of the billion points that could have erased us from history.”

We started this chapter with three points: Life wants to be; life doesn’t always want to be much; life from time to time goes extinct. To this we may add a fourth: Life goes on. And often, as we shall see, it goes on in ways that are decidedly amazing.

HERE AND THERE in the Natural History Museum in London, built into recesses along the underlit corridors or standing between glass cases of minerals and ostrich eggs and a century or so of other productive clutter, are secret doors—at least secret in the sense that there is nothing about them to attract the visitor’s notice. Occasionally you might see someone with the distracted manner and interestingly willful hair that mark the scholar emerge from one of the doors and hasten down a corridor, probably to disappear through another door a little further on, but this is a relatively rare event. For the most part the doors stay shut, giving no hint that beyond them exists another—a parallel—Natural History Museum as vast as, and in many ways more wonderful than, the one the public knows and adores.

The Natural History Museum contains some seventy million objects from every realm of life and every corner of the planet, with another hundred thousand or so added to the collection each year, but it is really only behind the scenes that you get a sense of what a treasure house this is. In cupboards and cabinets and long rooms full of close-packed shelves are kept tens of thousands of pickled animals in bottles, millions of insects pinned to squares of card, drawers of shiny mollusks, bones of dinosaurs, skulls of early humans, endless folders of neatly pressed plants. It is a little like wandering through Darwin’s brain. The spirit room alone holds fifteen miles of shelving containing jar upon jar of animals preserved in methylated spirit.

Back here are specimens collected by Joseph Banks in Australia, Alexander von Humboldt in Amazonia, Darwin on theBeagle voyage, and much else that is either very rare or historically important or both. Many people would love to get their hands on these things. A few actually have. In 1954 the museum acquired an outstanding ornithological collection from the estate of a devoted collector named Richard Meinertzhagen, author ofBirds of Arabia , among other scholarly works. Meinertzhagen had been a faithful attendee of the museum for years, coming almost daily to take notes for the production of his books and monographs. When the crates arrived, the curators excitedly jimmied them open to see what they had been left and were surprised, to put it mildly, to discover that a very large number of specimens bore the museum’s own labels. Mr. Meinertzhagen, it turned out, had been helping himself to their collections for years. It also explained his habit of wearing a large overcoat even during warm weather.

A few years later a charming old regular in the mollusks department—“quite a distinguished gentleman,” I was told—was caught inserting valued seashells into the hollow legs of his Zimmer frame.

“I don’t suppose there’s anything in here that somebody somewhere doesn’t covet,” Richard Fortey said with a thoughtful air as he gave me a tour of the beguiling world that is the behind-the-scenes part of the museum. We wandered through a confusion of departments where people sat at large tables doing intent, investigative things with arthropods and palm fronds and boxes of yellowed bones. Everywhere there was an air of unhurried thoroughness, of people being engaged in a gigantic endeavor that could never be completed and mustn’t be rushed. In 1967, I had read, the museum issued its report on the John Murray Expedition, an Indian Ocean survey, forty-four years after the expedition had concluded. This is a world where things move at their own pace, including a tiny lift Fortey and I shared with a scholarly looking elderly man with whom Fortey chatted genially and familiarly as we proceeded upwards at about the rate that sediments are laid down.

When the man departed, Fortey said to me: “That was a very nice chap named Norman who’s spent forty-two years studying one species of plant, St. John’s wort. He retired in 1989, but he still comes in every week.”

“How do you spend forty-two years on one species of plant?” I asked.

“It’s remarkable, isn’t it?” Fortey agreed. He thought for a moment. “He’s very thorough apparently.” The lift door opened to reveal a bricked-over opening. Fortey looked confounded. “That’s very strange,” he said. “That used to be Botany back there.” He punched a button for another floor, and we found our way at length to Botany by means of back staircases and discreet trespass through yet more departments where investigators toiled lovingly over once-living objects. And so it was that I was introduced to Len Ellis and the quiet world of bryophytes—mosses to the rest of us.

When Emerson poetically noted that mosses favor the north sides of trees (“The moss upon the forest bark, was pole-star when the night was dark”) he really meant lichens, for in the nineteenth century mosses and lichens weren’t distinguished. True mosses aren’t actually fussy about where they grow, so they are no good as natural compasses. In fact, mosses aren’t actually much good for anything. “Perhaps no great group of plants has so few uses, commercial or economic, as the mosses,” wrote Henry S. Conard, perhaps just a touch sadly, inHow to Know the Mosses and Liverworts , published in 1956 and still to be found on many library shelves as almost the only attempt to popularize the subject.

They are, however, prolific. Even with lichens removed, bryophytes is a busy realm, with over ten thousand species contained within some seven hundred genera. The plump and statelyMoss Flora of Britain and Ireland by A. J. E. Smith runs to seven hundred pages, and Britain and Ireland are by no means outstandingly mossy places. “The tropics are where you find the variety,” Len Ellis told me. A quiet, spare man, he has been at the Natural History Museum for twenty-seven years and curator of the department since 1990. “You can go out into a place like the rain forests of Malaysia and find new varieties with relative ease. I did that myself not long ago. I looked down and there was a species that had never been recorded.”