Nomenclatural Stability – What this really means.

Elseya branderhorsti. Photo by Arthur Georges

Elseya branderhorsti. Photo by Arthur Georges

I see a lot of discussion about stability. In particular people arguing that name changes should not be made on the grounds of stability. That genera or species should not be split on the grounds of Stability. The argument as to whether or not these splits should occur is a taxonomic one, whether species should be moved to other genera is a taxonomic one. Stability has no place in this argument.

The argument generally, as an example, goes that it is inconvenient to split the genus because it causes detachment to the prior literature. In my experience this is actually an over-inflated non-issue, generally being bantered as an excuse not to use their real reason which is that they just do not wish to change the name. This came up repeatedly in discussions recently on the splitting of the genus Anolis and in the past has come up over the genus Rana. As I said whether or not there is a case to split or not to split either of those genera is taxonomic and should be based on science, not dogma.

This argument is also unequally applied, which further discredits this entire argument. When people split Bothrops, or Emydura up, no one cared, same goes for Typhlops and many other genera. Why because it really does not matter. Yet when its suggested for Rana or Anolis we have heated debate which constantly descends into non scientific, dogmatic viewpoints. This is about politics, not science, it’s not even nomenclature.

So how does Stability apply here. It does not and that is my point. Before people argue for stability of nomenclature they should probably figure out what it is. Stability is actually referring to the maintenance of prevailing usage. In particular, as examples, it refers to names that have been forgotten for whatever reason, generally referred to as nomen oblitum, or possibly names of unclear taxa (nomen dubium) for which new information becomes available.

The idea is basically that if a name has not been used since 1899 or has not appeared in at least 50 articles in 10 different journals in the last 50 years, then the name is forgotten and prevailing usage then permits us to reverse the priority (effectively ignoring the Principal of Priority) and continue to use the younger and far better known younger name. So this is just about names, ie two synonymous species names or two synonymous genus names. Where an older, available, but unused name is not used in favor of a younger name. It has nothing to do with which species goes with which genus, referred to as the combination, as that is a taxonomic decision.

So what about the combination then is there any valid reason to protect it? Not under nomenclature. The ICZN Code has no say in this and should not, it goes beyond their mandate of only dealing with nomenclature and leaving taxonomy to taxonomists. However I will depart a little and express a view on this.

To me whether to split or lump should be based on the science, ie the phylogeny. Yes it is a subjective decision somewhat where one will name clades and where they will not, with regards to genera. As many authors have differing opinions on this and there are many species and several genus concepts about there is bound to be disagreement on this. What I disagree with though is having the a-priori view of not splitting on the grounds only of the inconvenience it may cause. People should be cautious for sure but if a better and more useful nomenclature for a group involves splitting a genus, and evidence for this is presented, then it should be possible to do it. I do not agree that paraphyly is the only reason for splitting genera.

The paraphyly argument is frequently brought up, this is where a clades immediate ancestor clade, with the same name, has another named clade in its descendants. This is not permitted in taxonomy, and correctly so, all I am saying is this is not the only reason for splitting.

Well that is a little about stability, it is a nomenclatural concept and has no place in taxonomy or conservation. I have frequently stated that you must separate taxonomy and nomenclature into its separate issues when confronting issues in the names of species. This one is a specific case of where this is important.


2 thoughts on “Nomenclatural Stability – What this really means.

  1. Peter Paul VanDijk

    Good article, one minor issue to pick on:

    “The paraphyly argument is frequently brought up, this is where a clade’s immediate ancestor clade, with the same name, has another named clade in its descendants. This is not permitted in taxonomy, and correctly so, all I am saying is this is not the only reason for splitting.”



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