Bill Bryson - A short history of nearly everything

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 1760s. 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. [36]

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 reestablish order, the British in 1842 proclaimed a new set of rules called the Stricklandian Code, but the French saw this as highhanded, 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 all organisms. A few phyla are generally well known, such as mollusks (the home of clams and snails), arthropods (insects and crustaceans), and chordates (us and all other animals with a backbone or protobackbone), though things then move swiftly in the direction of obscurity. Among the latter 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 nonbotanists 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 .

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 3 million to 200 million. More extraordinary still, according to a report in the Economist, as much as 97 percent 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 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 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.