I am responding to some recent discussions (several threads) in which CKing wrote, among other stuff:

“Ignoring taxonomic proposals is indeed an option. For example, Kluge proposed that the genus Chondropython should be synonymized with the genus Morelia because recognizing Chondropython renders Morelia paraphyletic. Both names are available under the rules of the ICZN, but I disagree with Kluge's proposal because it is based on an intolerance of paraphyletic taxa. Such disagreements are based on classificatory philosophy and are well known among taxonomists. Therefore it is unlikely that my disagreemnt with Kluge will be published in a journal. Nevertheless nobody is required by the ICZN to follow Kluge's taxonomic proposal nor is anyone required to publish a paper refuting Kluge. The customary practice is for each person to review the evidence presented by an author and to either accept or reject the proposal based on one's own evaluation of the evidence.”

and

”The rules cannot be used to settle taxonomic disputes between different schools of taxonomy, such as those between the Hennigians and the Darwinians. The rules are silent on the acceptability of paraphyletic taxa and will likely remain so forever. Therefore there is nothing in the rules that would require anyone to splinter paraphyletic taxa nor is there anything in the rules that requires anyone to follow taxonomic proposals that are meant to disqualify or destroy paraphyletic taxa. Conversely, no Hennigian is required by the rules to accept paraphyletic taxa. However, the stated purpose of the ICZN is to promote taxonomic stability. Hence one can very well argue that the stated purpose and the very existence of the ICZN are both contradictory to the taxonomic instability that is the direct result of the Hennigian's intolerance of paraphyletic taxa.”

Kluge’s (1993) classification of pythons is an interesting case in regard to the anti-Hennigian crusade CKing is all het up about. It presents two neat examples of nomenclatural changes made to produce a monophyletic classification (on the assumption the preferred cladogram accurately represents history, i.e. is a true phylogenetic tree): the sinking of Chondropython (into Morelia) and the splitting of Liasis (into Antaresia, Leiopython, Bothrochilus, Liasis and Apodora). To a non-dogmatist, each should be considered independently on its merits.

Speaking of dogma, this talk of ‘Hennigians vs. Darwinians’ reminds me of Lysenko, who also claimed to be a good Darwinian in his attacks on the Morganist-Weismannists (e.g. ‘The Situation in Biological Science’, 1948). If there really is a Darwinian school of taxonomy, it could be based on what Darwin actually had to say on the subject (‘On the Origin of Species’, Ch. XIV):
“No doubt organic beings, like all other objects, can be classed in many ways, either artificially by single characters, or more naturally by a number of characters… Some authors look at it merely as a scheme for arranging together those living objects which are most alike, and for separating those which are most unlike… I believe that community of descent – the one known cause of close similarity in organic beings – is the bond, which though obscured by various degrees of modification, is partly revealed by our classifications.”

Right on, Mr D! Let’s base our classification on our best hypothesis of ‘community of descent’ (i.e. monophyly, or holophyly if you insist on a distinction), as soon as we have enough evidence (‘number of characters’) to be reasonably sure of the actual patterns, and not be misled by the ‘various degrees of modification’ (i.e. symplesiomorphy in paraphyletic assemblages, and autapomorphy in certain specialized lineages).

Suppose we would like to know “What species is/are the closest genealogical relatives of Green pythons?” or “What other species is/are most similar to Green pythons in morphology, ecology and behaviour?” What use is a classification going to be in finding answers? It depends: if we’re working with the ‘traditional’ classification that CKing prefers, with a distinct genus Chondropython, the answer is “none at all”, whereas if the species is called Morelia viridis and Morelia is a monophyletic group, we will be able to infer that Green pythons are most closely related (had most recent common ancestry with), and most likely quite similar in biology to (one, some or all) other species of Morelia. In either case, it may be necessary to get behind the classification to the cladogram (or more complicated phylogeny) and raw data, but this is an easier process with one set of names than the other.

Keeping the name ‘Chondropython’ is a bit like Steven King going back to writing under pseudonyms: the product is simply WORTH MORE, these days, if the name on the cover tells you where it actually comes from. Morelia viridis (or the M. viridis complex) is in fact a highly derived member of the M. spilota group, not a creation ex nihilo.

For the same reasons, when I found that the Miocene python Montypythonoides riversleighensis was not as distinctive as originally supposed by Smith and Plane 1985 (see also Kluge 1993), I had no problem sinking the genus into Morelia (Scanlon 2001. Memoirs of the Association of Australasian Palaeontologists 25: 1-35). I can’t say for sure whether M. riversleighensis is closer to the amethistina group, the spilota group in general, or (what it’s most similar to) oenpelliensis, but calling it a Morelia covers all these bases. Montypythonoides is a cute name but was (it turned out) as useless as Chondropython.

The Liasis situation is different in a few ways, and contradicts CKing’s claim that Kluge is (consistently) a ‘lumper’. Kluge’s departure from ‘tradition’ in this case is in splitting a group of more-or-less similar species (Liasis sensu lato) into numerous genera rather than sinking one useless name, making the binominal classification more complex and more redundant (adding several monotypic genera) rather than more streamlined and informative (information on suprageneric groups was instead added as a separate layer, using an indentation scheme). The most important difference, in my view, is that the Morelia spilota group was quite well resolved by Kluge’s character data (leaving no doubt that viridis belongs inside it), while the whole region of the tree between Morelia and Aspidites (i.e. Liasis s.l.) has a lot of short internal branches and conflicting characters, so the particular topology favoured by Kluge was quite weakly supported. I don’t blame him for choosing a method and running consistently with its implications, but I’ve continued to use Liasis in the broad and possibly paraphyletic sense, partly to justify slipping a fossil species into an existing genus when its exact phylogenetic position was uncertain (Scanlon and Mackness, 2002. A new giant python from the Pliocene Bluff Downs Local Fauna of northeastern Queensland. Alcheringa 25: 425-437). Liasis dubudingala (probably the largest snake in Australia’s history) is distinctive in a few ways, but to create a monotypic genus for it would have just created more clutter. There was not enough information to place it in any of Kluge’s genera, and in such a case of uncertain relationships and similar species, paraphyletic taxa are (I think, sometimes) better than some alternatives. (If unable to place it in a genus, no species name could be assigned under the Code, and anybody could have come along and named it later without).

But once the phylogeny is well resolved, paraphyletic taxa are just positively misleading: they group together species that are KNOWN not to be each others closest relatives, and I don’t think Mr Darwin would approve. Despite statements by Bob Carroll (1988 etc.) and some others, it is biologically meaningless to say that genera and families are objectively real even if paraphyletic.

And what about all those ‘contrived taxa that cannot be defined’? Are we talking definition or diagnosis? In either case, this phrase (much repeated, without a cited reference) sounds like empty rhetoric. It’s always possible to DEFINE a taxon either by listing its constituent species, or (as in PhyloCode) by various means such as ‘all organisms more closely related to X than to Y’ or ‘the most recent common ancestor of X and Y and all its descendants’. These definitions are unambiguous and logically guaranteed to be monophyletic, though assigning species to higher taxa, apart from the reference species actually named in the definitions, is still always a matter of evidence for a phylogenetic hypothesis.

And then there’s DIAGNOSIS. Theoretically, in the case of almost total evolutionary stasis in two or more successive outgroups to a clade, there may exist paraphyletic assemblages of species that truly cannot be split up and diagnosed using shared derived characters. To assert that this is the case in New World Elaphe or any other group would require thorough investigation of all morphological systems in the relevant species (Scott Thomson mentioned some turtle examples where a close look at morphology found diagnostic characters for groups discovered and defined using genetic data). And a cladist’s diagnosis (using only apomorphies) can be constructed for any tree, whether or not it is a true representation of phylogeny: compare those of Kluge (1993), and mine of Liasis s.l., based on Kluge’s data set, in Scanlon and Mackness (2002), which can’t both be true. Both represent perfectly adequate diagnoses, but I prefer the one that refrains from radical change to preceding systems because (in my opinion) such change is not justified by the state of knowledge of actual relationships. That’s the interim version of taxonomic stability; but once we know the true relationships, we can pick a monophyletic taxonomy that can stand for all time.

[ Reply To This Message ] [ Subscribe to this Thread ] [ Show Entire Thread ]