Evolution and paraphyly

Curtis Clark jcclark at CSUPOMONA.EDU
Tue Jun 17 16:51:46 CDT 1997

My apologies if this has been touched upon, but my eyes were starting to
glaze over in the middle of today's paraphyly offerings, and the
aftereffects of sedation for a minor medical procedure weren't helping. And
I probably should just keep my "mouth shut", but it seems to me a lot of
the correspondents are skirting around what I see as the major issue. I
accept that evolution is capabale of producing paraphyletic species. I
refuse to accept (from total lack of evidence) that evolution is capable of
producing paraphyletic groups of species, except in the special case that
they all descended from a previously paraphyletic species. Evolution could
not have produced Reptilia, for example, except indirectly by producing the
taxonomists that created it. The decision of which species to remove from a
group to make it paraphyletic (with the one exception mentioned above) is
always arbitrary. I'm not saying it is never well-informed, just that there
are always other well-informed alternatives.

It troubles me that people so vehemently defend paraphyly; I assume that
there must be specific paraphyletic groups that they hope to keep. And yet
in the history of classification of the land plants, there has been a
decades-long effort to do away with paraphyletic groups. Remember
Gymnospermae? It is now the monophyletic Phyla Ccyadophyta, Ginkgophyta,
Coniferophyta, and Gnetophyta, plus a host of extinct relatives. Rememeber
the formal name of the ferns + "fern-allies" (I don't :-). Now the
Lycophyta, Psilophyta, Pterophyta, Spenophyta, plus others. Remember the
inclusive Bryophyta? In the most recent _Biology of Plants_, the mosses,
liverworts, and hornworts each get their own phylum.

And all this is good, because it shows kinship more clearly, and because
kinship is the necessary basis of comparative biology. I can think of
possible reasons for maintaining specific paraphyletic taxa, in the process
of sorting out the actual relationships, but I think the blanket acceptance
of paraphyletic groups is hobbling to systematics.

Curtis Clark                       http://www.is.csupomona.edu/~jcclark/
Biological Sciences Department                     Voice: (909) 869-4062
California State Polytechnic University, Pomona    FAX:   (909) 869-4078
Pomona CA 91768-4032  USA                          jcclark at csupomona.edu

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