by Bill Bryson
He named one genus of plants Clitoria. Not surprisingly, many people thought him strange. But his system of classification was irresistible. Before Linnaeus, plants were given names that were expansively descriptive. The common ground cherry was called Physalis amno ramosissime ramis angulosis glabris foliis dentoserratis. Linnaeus lopped it back to Physalis angulata, which name it still uses. The plant world was equally disordered by inconsistencies of naming. A botanist could not be sure if Rosa sylvestris alba cum rubore, folio glabro was the same plant that others called Rosa sylvestris inodora seu canina. Linnaeus solved the puzzlement by calling it simply Rosa canina. To make these excisions useful and agreeable to all required much more than simply being decisive. It required an instinct—a genius, in fact—for spotting the salient qualities of a species.
The Linnaean system is so well established that we can hardly imagine an alternative, but before Linnaeus, systems of classification were often highly whimsical. Animals might be categorized by whether they were wild or domesticated, terrestrial or aquatic, large or small, even whether they were thought handsome and noble or of no consequence. Buffon arranged his animals by their utility to man. Anatomical considerations barely came into it. Linnaeus made it his life’s work to rectify this deficiency by classifying all that was alive according to its physical attributes. Taxonomy—which is to say the science of classification—has never looked back.
This 1805 engraving, “Cupid inspiring plants with love, in a tropical landscape,” illustrates the concept behind Linnaeus’s theories on the sexual nature of plants, upon which he based his entire system of classification. (Credit 23.6)
It all took time, of course. The first edition of his great Systema Naturae in 1735 was just fourteen pages long. But it grew and grew, until by the twelfth edition—the last that Linnaeus would live to see—it extended to three volumes and 2,300 pages. In the end he named or recorded some thirteen thousand species of plant and animal. Other works were more comprehensive—John Ray’s three-volume Historia Generalis Plantarum in England, completed a generation earlier, covered no fewer than 18,625 species of plants alone—but what Linnaeus had that no-one else could touch was consistency, order, simplicity and timeliness. Though his work dates from the 1730s, it didn’t become widely known in England until the 1760s, just in time to make Linnaeus a kind of father figure to British naturalists. Nowhere was his system adopted with greater enthusiasm (which is why, for one thing, the Linnaean Society has its home in London and not Stockholm).
Title page of the 1758 tenth edition of Linnaeus’s Systema Naturae, which grew from fourteen pages to 2,300 between the first edition of 1735 and Linnaeus’s death forty-three years later. (Credit 23.7)
Linnaeus was not flawless. He made room for mythical beasts and “monstrous humans” whose descriptions he gullibly accepted from seamen and other imaginative travellers. Among these were a wild man, Homo ferus, who walked on all fours and had not yet mastered the art of speech, and Homo caudatus, “man with a tail.” But then it was, as we should not forget, an altogether more credulous age. Even the great Joseph Banks took a keen and believing interest in a series of reported sightings of mermaids off the Scottish coast at the end of the eighteenth century. For the most part, however, Linnaeus’s lapses were offset by sound and often brilliant taxonomy. Among other accomplishments, he saw that whales belonged with cows, mice and other common terrestrial animals in the order quadrupedia (later changed to mammalia), which no-one had done before.
In the beginning, Linnaeus intended to give each plant only a genus name and a number—Convolvulus 1, Convolvulus 2 and so on—but he soon realized that that was unsatisfactory and hit on the binomial arrangement that remains at the heart of the system to this day. The intention originally was to use the binomial system for everything—rocks, minerals, diseases, winds, whatever existed in nature. Not everyone embraced the system warmly. Many were disturbed by its tendency towards indelicacy, which was slightly ironic as before Linnaeus the common names of many plants and animals had been heartily vulgar. The dandelion was long popularly known as the “pissabed” because of its supposed diuretic properties, and other names in everyday use included mare’s fart, naked ladies, twitch-ballock, hound’s piss, open arse and bum-towel. One or two of these earthy appellations may unwittingly survive in English yet. The “maidenhair” in maidenhair moss, for instance, does not refer to the hair on the maiden’s head. At all events, it had long been felt that the natural sciences would be appreciably dignified by a dose of classical renaming, so there was a certain dismay in discovering that the self-appointed Prince of Botany had sprinkled his texts with such designations as Clitoria, Fornicata and Vulva.
Watercolour illustration from Systema Naturae which reflected Linnaeus’s abiding preoccupation with sex. (Credit 23.8)
Over the years many of these were quietly dropped (though not all: the common slipper limpet still answers on formal occasions to Crepidula fornicata) and many other refinements introduced as the needs of the natural sciences grew more specialized. In particular, the system was bolstered by the gradual introduction of additional hierarchies. Genus (plural genera) and species had been employed by naturalists for over a hundred years before Linnaeus, and order, class and family in their biological senses all came into use in the 1750s and 60s. But phylum wasn’t coined until 1876 (by the German Ernst Haeckel), and family and order were treated as interchangeable until early in the twentieth century. For a time zoologists used family where botanists placed order, to the occasional confusion of nearly everyone.1
Linnaeus had divided the animal world into six categories: mammals, reptiles, birds, fishes, insects and “vermes,” or worms, for everything that didn’t fit into the first five. From the outset it was evident that putting lobsters and shrimp into the same category as worms was unsatisfactory, and various new categories such as mollusca and crustacea were created. Unfortunately these new classifications were not uniformly applied from nation to nation. In an attempt to re-establish order, the British in 1842 proclaimed a new set of rules called the Stricklandian Code, but the French saw this as high-handed, and the Société Zoologique countered with its own conflicting code. Meanwhile, the American Ornithological Society, for obscure reasons, decided to use the 1758 edition of Systema Naturae as the basis for all its naming, rather than the 1766 edition used elsewhere, which meant that many American birds spent the nineteenth century logged in different genera from their avian cousins in Europe. Not until 1902, at an early meeting of the International Congress of Zoology, did naturalists begin at last to show a spirit of compromise and adopt a universal code.
Taxonomy is described sometimes as a science and sometimes as an art, but really it’s a battleground. Even today there is more disorder in the system than most people realize. Take the category of the phylum, the division that describes the basic body plans of organisms. A few phyla are generally well known, such as molluscs (the home of clams and snails), arthropods (insects and crustaceans) and chordates (us and all other animals with a backbone or proto-backbone); thereafter, things move swiftly in the direction of obscurity Among the obscure we might list gnathostomulida (marine worms), cnidaria (jellyfish, medusae, anemones and corals) and the delicate priapulida (or little “penis worms”). Familiar or not, these are elemental divisions. Yet there is surprisingly little agreement on how many phyla there are or ought to be. Most biologists fix the total at about thirty, but some opt for a number in the low twenties while Edward O. Wilson in The Diversity of Life puts the number at a surprisingly robust eighty-nine. It depends on where you decide to make your divisions—whether you are a “lumper” or a “splitter,” as they say in the biological world.
At the more workaday level of species, the possibilities for disagreements are even greater. Whether a species of grass should be called Aegilops incurva, Aegilops incurvata or Aegilops ovata may not be a matter that would stir many non-botanists to passion, but it can be a source of very lively heat in the right quarters.
The problem is that there are five thousand species of grass and many of them look awfully alike even to people who know grass. In consequence, some species have been found and named at least twenty times, and there are hardly any, it appears, that haven’t been independently identified at least twice. The two-volume Manual of the Grasses of the United States devotes two hundred closely typeset pages to sorting out all the synonymies, as the biological world refers to its inadvertent but quite common duplications. And that is just for the grasses of a single country.
To deal with disagreements on the global stage, a body known as the International Association for Plant Taxonomy arbitrates on questions of priority and duplication. At intervals it hands down decrees, declaring that Zauschneria californica (a common plant in rock gardens) is to be known henceforth as Epilobium canum; or that Aglaothamnion tenuissimum may now be regarded as conspecific with Aglaothamnion byssoides, but not with Aglaothamnion pseudobyssoides. Normally these are small matters of tidying up that attract little notice, but when they touch on beloved garden plants, as they sometimes do, shrieks of outrage inevitably follow. In the late 1980s the common chrysanthemum was banished (on apparently sound scientific principles) from the genus of the same name and relegated to the comparatively drab and undesirable world of the genus Dendranthema.
Chrysanthemum breeders are a proud and numerous lot, and they protested to the real-if-improbable-sounding Committee on Spermatophyta. (There are also committees for Pteridophyta, Bryophyta and Fungi, among others, all reporting to an executive called the Rapporteur-Général; this is truly an institution to cherish.) Although the rules of nomenclature are supposed to be rigidly applied, botanists are not indifferent to sentiment, and in 1995 the decision was reversed. Similar adjudications have saved petunias, euonymus, and a popular species of amaryllis from demotion, but not many species of geraniums, which some years ago were transferred, amid howls, to the genus Pelargonium. The disputes are entertainingly surveyed in Charles Elliott’s The Potting-Shed Papers.
Specimen cases of beetles, the most numerous and varied of all insects, with over 250,000 types recorded. Beetles occur everywhere on Earth except in the oceans and near the poles. (Credit 23.9)
Disputes and reorderings of much the same type can be found in all the other realms of the living, so keeping an overall tally is not nearly as straightforward a matter as you might suppose. In consequence, the rather amazing fact is that we don’t have the faintest idea—“not even to the nearest order of magnitude,” in the words of Edward O. Wilson—of the number of things that live on our planet. Estimates range from three million to two hundred million. More extraordinary still, according to a report in The Economist as much as 97 per cent of the world’s plant and animal species may still await discovery.
Of the organisms that we do 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. In The 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 in which we find ourselves 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 seventy thousand, others at a hundred thousand—nearly half as many again. You can find confident assertions that the number of described earthworm species is four thousand and equally confident assertions that the figure is twelve thousand. For insects, the numbers run from 750,000 to 950,000 species. These are, you understand, supposedly the known 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 non-controversial creatures. Goodness knows what the results would be if anyone attempted a similar exercise with the planet’s estimated twenty thousand types of lichens, fifty thousand species of mollusc or four-hundred-thousand-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 rainforest 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 twelve hundred types of beetle. On the basis of 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.
American entomologist Terry Erwin blasting rainforest trees with insecticide fog. Erwin has estimated that the number of insect species on Earth could be as high as 30 million. (Credit 23.10)
According to the Wall 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, the Journal adds, because of the cost (about £1,250 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 journal Nature a few months earlier, 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 taxon2 to 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 pap
er.
In an attempt to haul things into the modern age, in 2001 Kevin Kelly, co-founder of Wired magazine, launched an enterprise called the All Species Foundation with the aim of finding and recording on a database every living organism. The cost of such an exercise has been estimated at anywhere from £1.3 billion to as much as £30 billion. As of the spring of 2002, the foundation had just £750,000 in funds and four full-time employees.
If, as the numbers suggest, we have perhaps a hundred 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.
Greatly magnified micrograph of the house dust mite, Dermatophagoides pteronyssinus, which lives off the scales of human skin found in household dust. The average pillow alone may be home to forty thousand of these microscopic mites. (Credit 23.11)
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 2 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 Centre. (But at least they are your mites. Think of what you snuggle up with each time you climb into a hotel bed.)3 These mites have been with us since time immemorial, but they weren’t discovered until 1965.
