Living Words: the politics of taxonomic objects

During the first world war, according to a hoary old tale, the message was sent from the trenches to the command post behind the main front of the British Army from soldier to soldier. The message was sent as Send reinforcements, we're going to advance, but was received as Send three and fourpence, we're going to a dance. As things are transmitted, they change. School children are often introduced to this as the game "postman".

Change of things passed on seems to be inevitable. In biological history, of course, we call this evolution; but elsewhere we just call it change. Like all of culture, science changes too. Ideas are formed at one time for a reason and become different, or are abandoned, or we give them fresh life in ways that we didn't expect before.

Some of these ideas are the taxonomic ranks that go by the name of Linnaean. Linnaeus - also known as Carl von Linné (1707-1770) - was a Swedish botanist in the 18th century. He is responsible for a wave of enthusiasm that swept Europe for collecting and naming species of plants and animals, and he set up the tradition from which Charles Darwin ultimately sprang to form evolutionary theory pretty much as we now have it.

Linnaeus proposed five ranks, in his massive Systema Naturae, the tenth edition of which (1759, exactly a century before the Origin of Species) is the standard reference for species and genus names. If Linnaeus names it in that book, and someone else named it elsewhere, before or after, Linnaeus' names take priority. He named, for example, Homo sapiens.

Incidentally, these binomials, as they are called are the genus and species names. The species name is called the epithet of the species, and they are always printed in italics, by convention. The genus name is often abbreviated as a single letter, once it has been spelled out in a paper or book, and species epithets are always lowercased. So, for example, we have T. rex and H. sapiens, but never Sapiens or Rex.

Now, genus and species are logical terms based on the categories of logic developed first by Aristotle. They simply mean the general term and the specific term in categories. In that logic a species can be a genus for an even more specific term, but Linnaeus made them fixed ranks at the bottom, so that what we call a species in biology is what a traditional logician would know as an infimae species or "lowest specific term".

The ranks above them, though, are our focus today. Linnaeus, in big letters an inch or so high, begins with a political analogy: all reality is an Empire of Nature. Imperialism is a dirty word now, but in those days the most noble political organisation was, of course, the Roman Empire. The Holy Roman Empire still had some cachet too, although Linnaeus and his nation were firmly Lutheran, and he had trained in Protestant Holland. Nature is an empire, and it is ruled, of course by the Emperor, God.

The other ranks in his taxonomy were:

Regnum (Kingdom),
Classis (Class),
Ordo (Order),

And below the species he had another logical object - the Variety (varietas), which is an "individual" in logical terms, and not a class term. When you get to varieties, you have gotten to individuals, quite literally in Linnaeus' system.

Any botanist or zoologist will notice that we are missing two ranks. In the Linnaean taxonomy that ruled unchallenged (mostly!) for nearly two centuries, there are two other ranks that Linnaeus did not name. And one of them is particularly important in recent evolutionary discussions: phylum.

All these terms are political terms too: kingdoms naturally, to an eighteenth century naturalist (the term biologist being independently coined around 1800 by Trevarius and Lamarck), fall under an empire. Classes are obvious - there were the aristocracy, the middle class or bourgeois, and of course the peasantry or rustic class. And "order" is a name used for religious bodies as well as knighthoods ( social rank Linnaeus himself received some years later).

Linnaeus had a general term for these groups, no matter what the rank - and it was a military one; phalanx, the term for the highly organised ranks of the Greek armies that conquered the world and left Europe in its thrall throughout the Enlightenment and afterwards. The term did not catch on, and we had a number of proposals for "neutral" terms for taxonomic groups - one of the best known being taxon (from the Greek for division, around 1927), and another being deme from the Greek for "people", in the sense of population. Deme came later to mean a local breeding population, despite the best attempts of its coiner.

As Linnaeus' phalanxes marched on through the new science of biology, under the two kingdoms of plants for botany and animals for zoology (and minerals, but again Linnaeus was unsuccessful with his mineral species - they didn't seem to make sense, and eventually his classification scheme was abandoned for the current scheme of igneous, sedimentary and metamorphic rocks, etc.), it became clear that Linnaeus' scheme was not enough.

He thought that there were a relatively small number of species, genera and the other taxa (or phalanxes), each defined by a small number of characters - he wrote in an appendix to one of his works that all plants were definable by three characters with 60 variant forms each, giving a maximum of 60³ = 216,000 maximum of plant species. We now have millions described.

So at a point early in the nineteenth century it became necessary to increase the number of ranks to accommodate this increase of species. Two terms were introduced. One  is due to a predecessor of Linnaeus, Joseph Tournefort (1656-1708), who proposed that things be organised into "families". The term Family was interposed between Order and Genus, in keeping with Linnaeus' conception of the divine society of nature. But the other term - phylum - is the invention in 1817 of Cuvier, and it has come to have a distinctly evolutionary meaning.

Cuvier noted that animals (the kingdom) fell into four major groups that were higher than Orders. He called them, in French embranchements, or "branches", but with not the slightest hint that these were historical branches. His main opponents in that respect were Lamarck and his follower Geoffroy, who had proposed a scale of evolution. In his Regne Animales, Cuvier called these embranchments by the Greek word phylum (phulon, meaning a race, tribe, or class; more politics).

Modern readers may know that Stephen Jay Gould felt that there was sufficient difference in phyla to pose an evolutionary conundrum. In Wonderful Life (1991), Gould proposed the reality of bauplans, a German loanword meaning "builder's plans" or "blueprints" as we would say. These bauplans constrained later evolution, he thought. Others note that this is true of any level or rank in the taxonomic scheme. But there has been an even more radical revision of Linnaeus' ranks of quasipolitical organisms.

Classification is the process of putting things into classes, or "kinds". At the time Linnaeus wrote it was thought that these classes were "thoughts in the mind of God", a view that can be traced back to the teacher of Aquinas, Albertus Magnus. But today we think of these classes as ways to summarise the properties of natural things (or as convenient ways to order things, such as books, but we'll leave the conventional aspect to one side for now).

This granted, that classifications should be "natural", biologists have found that there are an indefinitely large number of levels or ranks, and that these do not match up from group to group. Under a methodology of classification now used called cladistics (from the Greek word for branches), there are as many levels in the tree of classification as there are speciation events between the outgroup and the particular species. There are no fixed ranks.

Oddly, this is more like the classification scheme of traditional, medieval, logic, although they too thought there were a set number of levels in God's mind. But this was due to Aristotle's metaphysics rather than his logic.

So, instead of Linnaeus' serried ranks of armies of organisms arranged neatly and hierarchically into divine patterns or battle formations, we have classifications as hypotheses that can now be tested by different characters or by adding other taxa into the analysis. This is more scientific. Is it less political?

No, it isn't. If there is any science that is political, it is taxonomy. Taxonomists become highly charged with emotion and verve when their preferred ideas are under threat. It is not hard to see why - apart from the fact that change means, as it does to all scientists, that they have to relearn their speciality, it also means that their own work under the now-outdated model is worth less than it was. Scientists live and die (as scientists) by the value of their work. Remove that, and you remove the very thing that drives science - credit. Credit is, as philosopher David Hull has argued in a seminal work, Science as a Process (1989), the "fitness" of the evolution of science.

Recently, this has come to a head with a proposal known as the Phylocode, which is intended to replace Linnaean classifications with something based on the phylogenetic (evolutionary) history of the species. There are those opposed and those in favour, and the two groups are treating this with all the gusto required by the Kissinger dictum (Academic politics are so vicious because the stakes are so low, which he took from someone else in a fine irony). I watch one botanist break down in tears when he responded to Brent Mishler, of the University of California, Davis, arguing in its favour. Why is this?

The Phylocode applies on the assumption that we must name groups according to how they evolved. To that end, it assumes that cladistic trees, or cladograms, are accurate and reliable representations of the evolutionary history. The Linnaean ranks, now at around 18 levels what with Tribes (another political term!) being introduced, and sub-tribes, super-orders and the like now installed, simply cannot cope with the complexity of actual evolution as determined by cladistics. But not even all cladists agree with the Phylocode. Gary Nelson, a famous opponent of what has become known as process cladism (the view that cladograms equal evolutionary trees directly), has argued against it in seminars and conferences. Gary was my PhD supervisor, so I must declare my interest here.

Gary's and others' (such as Norman Platnick at the AMNH where Gary used to be curator of fishes) argument against Phylocode is this, and it relies on that conventional aspect of classifications I ignored above: one primary task of classification is to allow specialists to talk to each other, and to impart some shared information in doing so. A specialist in spiders agreed when I spoke to him about this, noting that if someone says a spider is a Mygalomorph, then he knows it is a hunting spider with retractable downward facing fangs, which probably hunts alone at night, and is not a web-spinner. The Linnaean classifications carry information that the phylogenetic classifications do not.

Note, however, that Gary and his colleagues believe this is a matter of convention and ease of communication. These classifications are not natural classifications, and conclusions about the organisms cannot be drawn from them - you cannot, for example, compare the rates of evolution of higher taxa like an Order, because there is nothing to compare - Orders are artificial. Someone as far removed from Gary's pattern cladism (the view that cladograms mark patterns in the ways traits are distributed, and need further interpretation to become evolutionary trees - in fact they test evolutionary trees) as John Maynard Smith, who died just recently and will be sorely missed, agreed - taxa - all taxa in his case - are just conveniences to biologists.

And this is something Linnaeus himself admitted. He did not think that what we call the Linnaean system was anything more than a convenient way to teach and communicate. He made a few sketches for a natural system, but it didn't work any more than any of the other natural systems (including Tournetfort's) did, until cladistics came upon the scene.

So now we are here - no longer do we think the world is organised by God into neat hierarchical ranks of armies, so much as we think that evolution is the cause of things looking treelike. From an analogy with the political realities of human society, we use a metaphor of organic growth and differentiation, one we get directly from Darwin himself.

Will Phylocode win out? If it does, what are the implications? Science is not organised like Linnaeus' phalanaxes either - it is a democracy and a marketplace of ideas. Like deomcracies and marketplaces throughout history, it is a terribly messy and inefficient way to test ideas and find the value of things, except, as Churchill noted, for every other system ever tried. People have tried to force science to behave in a civil manner and to remain on economic or political target, but every time the result has been moribund and corrupt research.

Phylocode will win out if it makes the science more reliable, easier or generates some research that would not otherwise be done, and which is effective. This is always why ideas are adopted in science. It is a democracy, but a democracy of fierce pragmatists. They do not construct the reality they study, despite what the social constructionists may think, so much as have it thrust upon them. I think Phylocode will fail; but I might be wrong.

In one way this is like the argument librarians have between the merits of the Dewey decimal system or the Library of Congress system. Similarly, with computers, it may not matter. We might be able to maintain both, so long as at the specific level they coincide. But defining units of anything in science is at least partially a matter of being forced to do it by the evidence, by the data. Cladistics works for constructing hypotheses about relationships; it need not work as a way of teaching taxonomic traits or for communicating. Time will tell and in the end, it will depend on what works best. We shall see how these battles, and this politick, resolves itself in the future.

In the end, the dance of science, popular science and pseudoscience, and the politics and warfare of the ballroom floor, goes on, if you want my fourpenneth' worth...

A good treatment of Linnaeus is:

Stafleu, F.A. (1971) Linnaeus and the Linnaeans. The spreading of their ideas in systematic botany, 1735-1789. Oosthoek, Utrecht.

Gould's book is:

Gould, S.J. (1991) Wonderful life: the Burgess Shale and the nature of history. Penguin; Penguin Books Canada, London: Toronto.

The specifications and papers on the Phylocode proposal are available at <http://www.ohiou.edu/phylocode/> and Gary's arguments against it are at <http://www.systass.org/meetings/phylocode-debate.html> with links to other objectors such as Platnick. Discussion can be found here: <http://phylocode.miketaylor.org.uk/sitemap.html>.

Thanks to Wesley Elsberry and Ian Musgrave for constructive criticism and spell checking.