A short history of nearly everything - Bill Bryson [181]
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