Of the organisms that wedo know about, more than 99 in 100 are only sketchily described—“a scientific name, a handful of specimens in a museum, and a few scraps of description in scientific journals” is how Wilson describes the state of our knowledge. InThe Diversity of Life , he estimated the number of known species of all types—plants, insects, microbes, algae, everything—at 1.4 million, but added that that was just a guess. Other authorities have put the number of known species slightly higher, at around 1.5 million to 1.8 million, but there is no central registry of these things, so nowhere to check numbers. In short, the remarkable position we find ourselves in is that we don’t actually know what we actually know.

In principle you ought to be able to go to experts in each area of specialization, ask how many species there are in their fields, then add the totals. Many people have in fact done so. The problem is that seldom do any two come up with matching figures. Some sources put the number of known types of fungi at 70,000, others at 100,000—nearly half as many again. You can find confident assertions that the number of described earthworm species is 4,000 and equally confident assertions that the figure is 12,000. For insects, the numbers run from 750,000 to 950,000 species. These are, you understand, supposedly theknown number of species. For plants, the commonly accepted numbers range from 248,000 to 265,000. That may not seem too vast a discrepancy, but it’s more than twenty times the number of flowering plants in the whole of North America.

Putting things in order is not the easiest of tasks. In the early 1960s, Colin Groves of the Australian National University began a systematic survey of the 250-plus known species of primate. Oftentimes it turned out that the same species had been described more than once—sometimes several times—without any of the discoverers realizing that they were dealing with an animal that was already known to science. It took Groves four decades to untangle everything, and that was with a comparatively small group of easily distinguished, generally noncontroversial creatures. Goodness knows what the results would be if anyone attempted a similar exercise with the planet’s estimated 20,000 types of lichens, 50,000 species of mollusk, or 400,000-plus beetles.

What is certain is that there is a great deal of life out there, though the actual quantities are necessarily estimates based on extrapolations—sometimes exceedingly expansive extrapolations. In a well-known exercise in the 1980s, Terry Erwin of the Smithsonian Institution saturated a stand of nineteen rain forest trees in Panama with an insecticide fog, then collected everything that fell into his nets from the canopy. Among his haul (actually hauls, since he repeated the experiment seasonally to make sure he caught migrant species) were 1,200 types of beetle. Based on the distribution of beetles elsewhere, the number of other tree species in the forest, the number of forests in the world, the number of other insect types, and so on up a long chain of variables, he estimated a figure of 30 million species of insects for the entire planet—a figure he later said was too conservative. Others using the same or similar data have come up with figures of 13 million, 80 million, or 100 million insect types, underlining the conclusion that however carefully arrived at, such figures inevitably owe at least as much to supposition as to science.

According to theWall Street Journal , the world has “about 10,000 active taxonomists”—not a great number when you consider how much there is to be recorded. But, theJournal adds, because of the cost (about $2,000 per species) and paperwork, only about fifteen thousand new species of all types are logged per year.

“It’s not a biodiversity crisis, it’s a taxonomist crisis!” barks Koen Maes, Belgian-born head of invertebrates at the Kenyan National Museum in Nairobi, whom I met briefly on a visit to the country in the autumn of 2002. There were no specialized taxonomists in the whole of Africa, he told me. “There was one in the Ivory Coast, but I think he has retired,” he said. It takes eight to ten years to train a taxonomist, but none are coming along in Africa. “They are the real fossils,” Maes added. He himself was to be let go at the end of the year, he said. After seven years in Kenya, his contract was not being renewed. “No funds,” Maes explained.

Writing in the journalNature last year, the British biologist G. H. Godfray noted that there is a chronic “lack of prestige and resources” for taxonomists everywhere. In consequence, “many species are being described poorly in isolated publications, with no attempt to relate a new taxon37to existing species and classifications.” Moreover, much of taxonomists’ time is taken up not with describing new species but simply with sorting out old ones. Many, according to Godfray, “spend most of their career trying to interpret the work of nineteenth-century systematicists: deconstructing their often inadequate published descriptions or scouring the world’s museums for type material that is often in very poor condition.” Godfray particularly stresses the absence of attention being paid to the systematizing possibilities of the Internet. The fact is that taxonomy by and large is still quaintly wedded to paper.

In an attempt to haul things into the modern age, in 2001 Kevin Kelly, cofounder ofWired magazine, launched an enterprise called the All Species Foundation with the aim of finding every living organism and recording it on a database. The cost of such an exercise has been estimated at anywhere from $2 billion to as much as $50 billion. As of the spring of 2002, the foundation had just $1.2 million in funds and four full-time employees. If, as the numbers suggest, we have perhaps 100 million species of insects yet to find, and if our rates of discovery continue at the present pace, we should have a definitive total for insects in a little over fifteen thousand years. The rest of the animal kingdom may take a little longer.

So why do we know as little as we do? There are nearly as many reasons as there are animals left to count, but here are a few of the principal causes:

Most living things are small and easily overlooked.In practical terms, this is not always a bad thing. You might not slumber quite so contentedly if you were aware that your mattress is home to perhaps two million microscopic mites, which come out in the wee hours to sup on your sebaceous oils and feast on all those lovely, crunchy flakes of skin that you shed as you doze and toss. Your pillow alone may be home to forty thousand of them. (To them your head is just one large oily bon-bon.) And don’t think a clean pillowcase will make a difference. To something on the scale of bed mites, the weave of the tightest human fabric looks like ship’s rigging. Indeed, if your pillow is six years old—which is apparently about the average age for a pillow—it has been estimated that one-tenth of its weight will be made up of “sloughed skin, living mites, dead mites and mite dung,” to quote the man who did the measuring, Dr. John Maunder of the British Medical Entomology Center. (But at least they areyourmites. Think of what you snuggle up with each time you climb into a motel bed.)38These mites have been with us since time immemorial, but they weren’t discovered until 1965.

If creatures as intimately associated with us as bed mites escaped our notice until the age of color television, it’s hardly surprising that most of the rest of the small-scale world is barely known to us. Go out into a woods—any woods at all—bend down and scoop up a handful of soil, and you will be holding up to 10 billion bacteria, most of them unknown to science. Your sample will also contain perhaps a million plump yeasts, some 200,000 hairy little fungi known as molds, perhaps 10,000 protozoans (of which the most familiar is the amoeba), and assorted rotifers, flatworms, roundworms, and other microscopic creatures known collectively as cryptozoa. A large portion of these will also be unknown.

The most comprehensive handbook of microorganisms,Bergey’s Manual of Systematic Bacteriology , lists about 4,000 types of bacteria. In the 1980s, a pair of Norwegian scientists, Jostein Goksøyr and Vigdis Torsvik, collected a gram of random soil from a beech forest near their lab in Bergen and carefully analyzed its bacterial content. They found that this single small sample contained between 4,000 and 5,000 separate bacterial species, more than in the whole ofBergey’s Manual . They then traveled to a coastal location a few miles away, scooped up another gram of earth, and found that it contained 4,000 to 5,000other species. As Edward O. Wilson observes: “If over 9,000 microbial types exist in two pinches of substrate from two localities in Norway, how many more await discovery in other, radically different habitats?” Well, according to one estimate, it could be as high as 400 million.

We don’t look in the right places.InThe Diversity of Life , Wilson describes how one botanist spent a few days tramping around ten hectares of jungle in Borneo and discovered a thousand new species of flowering plant—more than are found in the whole of North America. The plants weren’t hard to find. It’s just that no one had looked there before. Koen Maes of the Kenyan National Museum told me that he went to one cloud forest, as mountaintop forests are known in Kenya, and in a half hour “of not particularly dedicated looking” found four new species of millipedes, three representing new genera, and one new species of tree. “Big tree,” he added, and shaped his arms as if about to dance with a very large partner. Cloud forests are found on the tops of plateaus and have sometimes been isolated for millions of years. “They provide the ideal climate for biology and they have hardly been studied,” he said.

Overall, tropical rain forests cover only about 6 percent of Earth’s surface, but harbor more than half of its animal life and about two-thirds of its flowering plants, and most of this life remains unknown to us because too few researchers spend time in them. Not incidentally, much of this could be quite valuable. At least 99 percent of flowering plants have never been tested for their medicinal properties. Because they can’t flee from predators, plants have had to contrive chemical defenses, and so are particularly enriched in intriguing compounds. Even now nearly a quarter of all prescribed medicines are derived from just forty plants, with another 16 percent coming from animals or microbes, so there is a serious risk with every hectare of forest felled of losing medically vital possibilities. Using a method called combinatorial chemistry, chemists can generate forty thousand compounds at a time in labs, but these products are random and not uncommonly useless, whereas any natural molecule will have already passed what theEconomist calls “the ultimate screening programme: over three and a half billion years of evolution.”

Looking for the unknown isn’t simply a matter of traveling to remote or distant places, however. In his bookLife: An Unauthorised Biography , Richard Fortey notes how one ancient bacterium was found on the wall of a country pub “where men had urinated for generations”—a discovery that would seem to involve rare amounts of luckanddevotion and possibly some other quality not specified.

There aren’t enough specialists.The stock of things to be found, examined, and recorded very much outruns the supply of scientists available to do it. Take the hardy and little-known organisms known as bdelloid rotifers. These are microscopic animals that can survive almost anything. When conditions are tough, they curl up into a compact shape, switch off their metabolism, and wait for better times. In this state, you can drop them into boiling water or freeze them almost to absolute zero—that is the level where even atoms give up—and, when this torment has finished and they are returned to a more pleasing environment, they will uncurl and move on as if nothing has happened. So far, about 500 species have been identified (though other sources say 360), but nobody has any idea, even remotely, how many there may be altogether. For years almost all that was known about them was thanks to the work of a devoted amateur, a London clerical worker named David Bryce who studied them in his spare time. They can be found all over the world, but you could have all the bdelloid rotifer experts in the world to dinner and not have to borrow plates from the neighbors.

Even something as important and ubiquitous as fungi—and fungi are both—attracts comparatively little notice. Fungi are everywhere and come in many forms—as mushrooms, molds, mildews, yeasts, and puffballs, to name but a sampling—and they exist in volumes that most of us little suspect. Gather together all the fungi found in a typical acre of meadow and you would have 2,500 pounds of the stuff. These are not marginal organisms. Without fungi there would be no potato blights, Dutch elm disease, jock itch, or athlete’s foot, but also no yogurts or beers or cheeses. Altogether about 70,000 species of fungi have been identified, but it is thought the number could be as high as 1.8 million. A lot of mycologists work in industry, making cheeses and yogurts and the like, so it is hard to say how many are actively involved in research, but we can safely take it that there are more species of fungi to be found than there are people to find them.

The world is a really big place.We have been gulled by the ease of air travel and other forms of communication into thinking that the world is not all that big, but at ground level, where researchers must work, it is actually enormous—enormous enough to be full of surprises. The okapi, the nearest living relative of the giraffe, is now known to exist in substantial numbers in the rain forests of Zaire—the total population is estimated at perhaps thirty thousand—yet its existence wasn’t even suspected until the twentieth century. The large flightless New Zealand bird called the takahe had been presumed extinct for two hundred years before being found living in a rugged area of the country’s South Island. In 1995 a team of French and British scientists in Tibet, who were lost in a snowstorm in a remote valley, came across a breed of horse, called the Riwoche, that had previously been known only from prehistoric cave drawings. The valley’s inhabitants were astonished to learn that the horse was considered a rarity in the wider world.

Some people think even greater surprises may await us. “A leading British ethno-biologist,” wrote theEconomist in 1995, “thinks a megatherium, a sort of giant ground sloth which may stand as high as a giraffe . . . may lurk in the fastnesses of the Amazon basin.” Perhaps significantly, the ethnobiologist wasn’t named; perhaps even more significantly, nothing more has been heard of him or his giant sloth. No one, however, can categorically say that no such thing is there until every jungly glade has been investigated, and we are a long way from achieving that.

But even if we groomed thousands of fieldworkers and dispatched them to the farthest corners of the world, it would not be effort enough, for wherever life can be, it is. Life’s extraordinary fecundity is amazing, even gratifying, but also problematic. To survey it all, you would have to turn over every rock, sift through the litter on every forest floor, sieve unimaginable quantities of sand and dirt, climb into every forest canopy, and devise much more efficient ways to examine the seas. Even then you would overlook whole ecosystems. In the 1980s, spelunkers entered a deep cave in Romania that had been sealed off from the outside world for a long but unknown period and found thirty-three species of insects and other small creatures—spiders, centipedes, lice—all blind, colorless, and new to science. They were living off the microbes in the surface scum of pools, which in turn were feeding on hydrogen sulfide from hot springs.

Our instinct may be to see the impossibility of tracking everything down as frustrating, dispiriting, perhaps even appalling, but it can just as well be viewed as almost unbearably exciting. We live on a planet that has a more or less infinite capacity to surprise. What reasoning person could possibly want it any other way?

What is nearly always most arresting in any ramble through the scattered disciplines of modern science is realizing how many people have been willing to devote lifetimes to the most sumptuously esoteric lines of inquiry. In one of his essays, Stephen Jay Gould notes how a hero of his named Henry Edward Crampton spent fifty years, from 1906 to his death in 1956, quietly studying a genus of land snails in Polynesia calledPartula . Over and over, year after year, Crampton measured to the tiniest degree—to eight decimal places—the whorls and arcs and gentle curves of numberlessPartula , compiling the results into fastidiously detailed tables. A single line of text in a Crampton table could represent weeks of measurement and calculation.

Only slightly less devoted, and certainly more unexpected, was Alfred C. Kinsey, who became famous for his studies of human sexuality in the 1940s and 1950s. But before his mind became filled with sex, so to speak, Kinsey was an entomologist, and a dogged one at that. In one expedition lasting two years, he hiked 2,500 miles to assemble a collection of 300,000 wasps. How many stings he collected along the way is not, alas, recorded.

Something that had been puzzling me was the question of how you assured a chain of succession in these arcane fields. Clearly there cannot be many institutions in the world that require or are prepared to support specialists in barnacles or Pacific snails. As we parted at the Natural History Museum in London, I asked Richard Fortey how science ensures that when one person goes there’s someone ready to take his place.

He chuckled rather heartily at my naiveté. “I’m afraid it’s not as if we have substitutes sitting on the bench somewhere waiting to be called in to play. When a specialist retires or, even more unfortunately, dies, that can bring a stop to things in that field, sometimes for a very long while.”

“And I suppose that’s why you value someone who spends forty-two years studying a single species of plant, even if it doesn’t produce anything terribly new?”

“Precisely,” he said, “precisely.” And he really seemed to mean it.