[Taxacom] Invisible evolution, paraphyly

[Richard Zander]

What I mean is that suppose you have three taxa, A, B and C. These
terminate a branch of a large tree thus: (A, B) C. A and B are more
closely related than they are to C.

Now suppose these three represent a monophyletic taxon Xus. But suppose
further research finds B is actually a taxon different from Xus (call it
Yus) at the same grade. Say, just to not introduce problems, Xus and Yus
are both categories higher than species. A and C are in Xus and B in
Yus. 

But then Xus is paraphyletic. We must either split the three into three
separate taxa at the same grade (Xus, Yus and Zus) or reject Yus. The
splitting is necessary to keep the whole bit monophyletic.

It may seem natural nowadays to do this splitting because monophyly has
been put forward as a neat way to get rid of problems with differing
species concepts. Everything can be compared on the same basis. It is
totally artificial, however, as Xus with A and C, as a paraphyletic
taxon, may be a morphologically, ecologically, and yes evolutionarily
coherent taxon, which, if split, destroys information. Phylogeny is not
evolution.

> -----Original Message-----
> From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-
> bounces at mailman.nhm.ku.edu] On Behalf Of Curtis Clark
> Sent: Wednesday, June 13, 2007 10:38 PM
> To: taxacom at mailman.nhm.ku.edu
> Subject: Re: [Taxacom] Invisible evolution, paraphyly
> 
> On 2007-06-12 07:33, Richard Zander wrote:
> > I see. A paraphyletic species remains integral, held together by
> > something, but amniotes minus birds and mammals isn't held together
by
> > anything and so is fair game for splitting.
> 
> I must not be understanding you. *Everyone* splits the Reptilia, into
> orders, families, genera, and species. Even Ken. One can split
> paraphyletic species, intot subspecies, varieties, and formas, or into
> populations, races, or ecotypes. So what?
> 

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Richard H. Zander 
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Missouri Botanical Garden
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