The Linnaean System vs Anything Else

As may be apparent by now, my primary interests are in the function and evolution in teeth … and precision in terminology. The latter is rather imprecise, as it is a feature of something greater: Precision in methodology. This includes nomenclature, so that i can say that if I see something, I have a name for it that is likely to be what someone else who — having never read anything I’ve written — will call it.

For the most part, systematic taxonomy gives scientists a die-hard process and reference to the nomenclature of organisms. There will always be different lay terms for things, especially as there continues to be different languages, but when it comes to scientific nomenclature, there should only be one thing. This allows me to talk about something like Oviraptor philoceratops, and not expect someone to pull up a discussion on “Ingenia” yanshini instead, or something else.

Systematic nomenclature, or taxonomy, is a neat, orderly system: We define for ourselves an organism, and if no one else has yet applied a name to that organism, we get to do so if we feel so inclined, or if it seems required. What becomes more problematic is whenwe want to name sets of organisms, be they lineages, populations of individuals, grades of organisms defined on the basis of a morphology, or an historical construct of a group of organisms. In the 1700s, one of the premier botanists of his day (Carolus Linnaeus) set out a system by which he catalogued and organized the plants he studied. He followed this by extending his system to all other groups of organisms (and rocks), and several decades later Linnaean Taxonomy took off. It has since been adopted almost universally by varied groups of biologists (and abandoned by geologists, for obvious reasons). But there are problems with it.

The Linnaean System should be familiar to anyone who reads this. While Linnaeus formulated rules for organisms, he started with the species, the basic unit of organism. But he noticed it would be necessary to encapsulate increasing levels of diversity, groups by their mutual similarities, and so the system continues on with the use of ranks. These are, for the sake of this discussion, familiar but requires repetition: Species, Genus, Family, Order, Class, Phylum, Kingdom. Linnaeus did not use all of these, and since his formulation some have added a few others, such as Domain, Cohort, etc.

Originally, taxa were only named to correspond to ranks; further breakdown of organismal diversity was unnecessary, because at the time, degrees of diversity were seen as absolute, following the adage “There is nothing new under the sun.” Linnaean was a religious man, and like most in his time, considered organismal diversity fixed, as set in the Creation by God. There was no need to recognize further diversity, as even the pattern of some of these organisms’ relationship (bats, as mammals, were grouped with birds, while whales, also mammals, were grouped with fish; this owed to the premise that proper mammals were terrestrial, and that the creatures of the sea and sky were set out by God in separate events). All neat and tidy.

Recognition of evolution, and the probably antiquity of organisms as well as the likely non-action of a Creation by God, led to a reconsideration for the organization of life, and steadily, up through the 1800’s and into the 1900’s, biology recognized that taxic diversity was not as neat and orderly. As noted, it became necessary for some systematists to invent new ranks to describe levels of biology they hadn’t recognized before. This reason is two-fold: 1) they regarded the rank as a valuable tool for classifying objects, while 2) they were loathe to move taxa around ranks. My premise here is that to many of these people, and many of them still work in biology today, view the existence of the rank as a valuable, working construct, a philosophical tool with which to view taxa apart from the organisms they describe. That ranks are tools is not an issue, but I here remark on the value of that tool.

Ranks have one glaring problem when it comes to taxonomy: Unlike the philosophical application of nomenclature to organisms, a scientific grouping of individuals into species, and species into groups of species, and above, ranks are meaningless without their concordant taxa. Remove a rank, and you have serially inclusive taxa, all the way from Animalia to Homo sapiens. Use of the terms Kingdom and Species (respectively) are effectively repetition when it comes to nomenclature that never deviates from the ranked position. We do not talk about Phylum Animalia, nor Family Sapiens. Not only has no one made such a proposition, no one will. This is unsound on a philosophical level (being illogical) and unscientific.

I should note that taxonomists do and will propose rank-changes for some taxa. In the early 1900’s, a grouop of biologists set up an organization known as the ICZN (the International Commission on Zoological Nomenclature, whose website is here); there is also an ICBN for plants (B is for Botany), and one for Bacteria (ICNB). The purpose of the ICZN was to call to an end, though mutual agreement, the acts of systematists naming the same animal many different things, and causing confusion over what, precisely, was being named. Today, the ICZN governs more than just naming organisms (it governs the ranks for Species, Genus, and Family — not taxa by themselves, but taxa associated with those ranks), it also governs the fixation of type specimens (so that we have AN organism from which to call something, and something to which we can compare further organisms, from biological specimens like DNA to fossil remains). It does so essentially by mutual consent; many institutions and most journals that publish systematics require adherence to one of these Codes, although some of the paleontological and fewer other scientific journals are permitting unranked nomenclature to be coined (these works still adhere to the fixation of types, issues of synonymy, etc.). The Code permits taxa to be moved up and down ranks, generally in relation to other organisms of the same “rank,” when recognition of a degree of variance implies this should be done. There are no rules on why this could be done, only what happens to the nomenclature when it does. This is one of the major issues with ranks versus nonranks and noted above: A rank can dictate the relative position of a taxon (and it can be reflected on how the name is formed), as well as force taxa to stay at or around a particular rank because of that nomenclatural formation.

For example, the genus/species combination (called a binomen) Homo sapiens represents an organism in two parts; sapiens is the label we provide for morphologically or genetically modern man, and it includes every human living today and in the past. There are also subspecies, superspecies, subgenera, supergenera, etc., and they related to partitioning or grouping of sets of subsets of these basic ranks, and they themselves are also ranks. When we wish to recognize types of human-like members of Homo, we will almost invariably refer them to Homo sapiens, or separate them into a new species, such as Homo neanderthalensis; but we will also consider that Neanderthal man is practically human, so we place neanderthalensis inside, rather than alongside, sapiens, and make it a subspecies, along with the former species that represented us. There is still a Homo sapiens though, although it isn’t the same kind; as we are now a subspecies, that species sapiens is a rank up, and we get the “new” taxa Homo sapiens sapiens, and Homo sapiens neanderthalensis. Systematists who use this system will even recognize the issue, and note that Homo sapiens with neanderthalensis next to it is the same as Homo sapiens sapiens with neanderthalensis next to it.

[I should have a pretty graphic up about this, but I haven’t time as I write this.]

With ranks, you see, there is an implied level of distinction that separates one from another. This distinxction has never been described, nor does it exist. Some systematics have used the system due to its prevalence, and others because they consider the taxic containers ranks provide useful, largely for phyletic reasons (i.e., conserns over degrees of difference, without quantification of the meaning of the difference, or the comparative value of that difference among taxa), but this is largely due to a philosophical desire to place concentric containers around nomenclature. But I tell you, a phylogeny with and without ranks is the same, making ranks effectively meaningless on their own; they are only useful when applied to taxa. So this argument begs the question: What use are ranks when ranks require the arrangement of taxa to be fixed to make them important? The answer is none. And with that, I call the slow death of the Linnaean System long overdue.

This is not meant to be a stab at the ICZN, current purveyors of the Linnaean System; the utility of the Code (found here) is that it provides a system of rules by with specimens are named, compared, considered, etc. I think for the most part, the ICZN will live n, but it has given rise to a contender for a rank-free system that is gaining a foothold in systematists of varying disciplines and zoological and botanical specialties: The PhyloCode. This post is not meant to be an advertisement for the PhyloCode, and the website I linked to can speak for itself. Rather, I wish to enforce the premise here that rank-free nomenclature is not only possible, it’s viable. So we can displense with the predilections that come with ranks, such as the inane need to split taxa through perceived degrees of difference without any other reason, or on a dependant desire to use ranks because they are there. Species concepts aside (and this faces not only dinosaurian systematics that I concern myself with [barely], but also hominid systematics such as the recently named Australopithecus sediba, which the authors themselves admit could just as easily have been a species placed in Homo; Homo sediba … not too hard, is it?).

[I will provide a short list of proper references and links later, largely to clean up the text. This was meant to be a quick post and became a monster, so you have my appologies.]

This entry was posted in Biology, Philosophy, Taxonomy and tagged , , , . Bookmark the permalink.

One Response to The Linnaean System vs Anything Else

  1. You need to add a retweet button to your blog. I just shared this post, but had to do it manually. Just my $.02 :)

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