Comments to Cladistics/Eclecticism: Precision & Priority
D.Walter at MAILBOX.UQ.EDU.AU
Sat Feb 9 09:43:07 CST 2002
Thank you for your interesting series of emails. I agree with some of what
you say, but I have a few quibbles I think are worth bringing up as general
>1. Taxa and clades [and your point 3]
>The term taxon is used with slightly different meanings by different
>people, even in the literature.
>Some people use taxon as a synonym to clade, i.e. a monophyletic group
>(NAMED OR NOT)... Other people use taxon to mean a NAMED monophyletic
>group, even others use it to mean
>a NAMED group of species (monophyletic or paraphyletic)... However, since
>I am a cladist
>(strict cladist for Ken), I will not use taxon to mean named group of
TAXON is a precladistic term and refers to any named rank in a taxonomic
hierarchy. I think I get this definition from Mayr's first book on
systematics, but in any case it is the preferred definition and the only
accepted one in pre-cladistic literature. This definition has priority, so
restricting it's use to clades is a special use of the term and needs to be
clarified by any author using it as a synonym for monophyletic groups or
any other variant that is not also a taxon in the original meaning.
>...For example, cladistics necessitates a phylogenetic species concept.
I know cladists that insist that only lineages exist and that species and
other taxa (even if defined cladistically) are convenient fictions. I also
know others that consider each and every branch as a real entity and see no
need for dwelling on species-level splits.
>The evolutionary taxonomists (eclecticists, Mayr-Simpsonites,
) on this list --
>and some people who call themselves cladists are entrapped in a
>morphological species concept.
>Cladistics is incompatible with a morphological species concept. [Also
>your point 7]
Hennig based his taxa primarily on morphology. I think you are making the
increasingly common mistake of confusing a typological species concept with
the use of morphology as a technique to distinguish species. Morphology
can be used with any species concept (there are over 20 that I know of),
just as molecular data could be used with any species concept (including a
typological or a phenetic concept of species). Also, molecular data does
not necessarily distinguish sibling species, especially if only a small
number of gene sequences are used. Even with mitochondrial genes, it's
fairly arbitrary where the line between species is drawn.
>>If you give a cladogram to a number of cladists, they all will delimit
>>the same groups. They will not disagree.
I think you are too optimistic. I've often questioned why certain clades
were named and others not.
>5. Are monophyletic and paraphyletic groups equally natural?
This is an interesting question, but as an alleged cladist I have to say no
and not think too much about reticulation. (If I were argumentative I
would point out that unknown [extinct, undiscovered] taxa are left out of
proposed monophyletic groups - but this *is* a furfy).
Here's a question I'm dreading some student asking me one day: "If the
symbiotic theory of evolution is correct, are the prokaryotic domains
paraphyletic and is Eukaryota polyphyletic?"
>Even though they look identical, they do not interbreed and are hence good
>species. [and several other similar comments in your list of points]
It's always a good idea to look closely at your assumptions before
developing a train of thought [not that I follow this advice]. You seem to
uncritically accept the Biological Species Concept [i.e. gene flow is the
conclusive and exclusive test of species]. Although the BSC is the usual
textbook dogma and forms the basis of the idea of species with which most
Western biologists have have been inculcated, it is a badly flawed
hypothesis that most practicing biologists either (1) accept but never
actually use to test species identities [some population biologists
excepted] (2) reject because it fails to deal with one or more
'problems' [e.g. hybridization and other reticulations, clones ...].
At least some of the arguments in several recent threads seem to hinge on
the dicotomy between those who think that species are real (which some
would expand to all taxa) and those that are primarily interested in
branching patterns. Several have raise the issue (at least for species),
but I don't see any consensus that this is the critical disagreement.
Cheers from and ecologist and systematist from Oz,
Dr David Evans Walter
Senior Lecturer & Coordinator for Entomology Flexible Learning
Department of Zoology & Entomology
Project Leader, Cooperative Research Centre for Tropical Plant Protection
The University of Queensland, St. Lucia Campus,
Brisbane, Queensland 4072 Australia
Tele. (61)(7) 3365-1564; Fax (61)(7) 3365-1922
Webpage = http://www.uq.edu.au/entomology/david.evans.walter.html
Mite Image Gallery = http://www.uq.edu.au/entomology/mite/mitetxt.html
Email = D.Walter at mailbox.uq.edu.au
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