A short history of nearly everything

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 are your mites. Think of what you snuggle up with each time you climb into a motel bed.)[38] These 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 Goksoyr 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 of Bergey’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 5,000 other 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. In The 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 the Economist 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 book Life: 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 luck and devotion 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 the Economist 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