2000 years of stasis
MAGarland at AOL.COM
MAGarland at AOL.COM
Sun Feb 6 13:16:28 CST 2000
In a message dated 2/5/00 4:01:42 PM Eastern Standard Time, Philip Cantino
> I certainly agree with Mark that identification is a very important
> activity and that any taxonomic system should facilitate identification.
> However, the kind of nomenclature that is used (phylogenetic or Linnaean)
> has no bearing on whether a classification (or rankless taxonomic system)
> is useful for identification.
I completely agree. But it seems to me that the kind of nomenclature that is
used *does* have a bearing on which things get named at all. And I can
imagine that, by naming clades, phylogenetic nomenclature will give us lots
of named things that are unidentifiable--or at least extremely hard to
identify. For example: Ghiselin (who seems to be invoked by proponents of
phylogenetic nomenclature) says that taxa are simply lineages--not only do
they not have *defining* characters, but they do not even need *diagnostic*
ones ("Definition," "character," and other equivocal terms, Systematic
Zoology 33: 106-107. 1984.).
> Phylogenetic nomenclature is
> not the only system that defines taxon names. Our traditional "Linnaean"
> system defines names by linking them with a rank and a type. We don't
> usually refer to this as a definition, but it functions as one. For
> example, in the current system, Lamiaceae is defined as the taxon of family
> rank that includes Lamium. In phylogenetic nomenclature, Lamiaceae might
> be defined as the least inclusive clade that contains Lamium and Congea.
I also agree, and was wrong to imply that only phylogenetic nomenclature
defines names. But the current system of definitions (the type method) is
simply a record-keeping device associating a name with (ultimately) a real
specimen: Lamiaceae is something that is at least Lamium, Lamium is at least
its type species (say L. purpureum--I don't know offhand), L. purpureum is at
least one specimen preserved somewhere. I'll even say that this is also
essentialistic, the types being the "essence" of the names. But the types do
*not* define the taxa themselves.
On the other hand, when you say that Lamiaceae is the clade containing Lamium
and Congea, I think that you are doing more than record-keeping (or
librarianship, as Peter Stevens I think referred to it). First, you are
divorcing the name from a visible object (specimen) and defining it as an
invisible lineage. Second, you think you know what's included in that
lineage--if you didn't, why did you choose Lamium and Congea to define it?
In other words, you are trying to define a particular branch on a
cladogram--and if a branch is a taxon, you are trying to define the *taxon
itself,* not just the *name.*
That's why I referred to essentialism earlier. You are assuming that you can
define the unchanging essence of a taxon (the common ancestor and all of its
descendents), not just the name of the taxon. Nelson and Platnick
(Systematics and Biogeography, p. 328. 1981) were so awed by the power of
cladistic techniques to create branching patterns that they came out in favor
of essentialism (or typology). In their case, the essence of a clade is its
synapomorphies, not its common ancestor and all of its descendents, but just
maybe they were more clear-headed about essentialism than most cladists.
I have to go out and look at some plants. My head hurts.
Mark A. Garland
Florida Department of Environmental Protection
2600 Blair Stone Road, Mail Station 2500
Tallahassee, Florida 32399
mark.garland at dep.state.fl.us
magarland at aol.com
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