[Taxacom] Invisible evolution, paraphyly

[Richard Zander]

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.

Yes, we have a species definition problem. A species is a basic unit of
taxonomy with usually two kinds of further special definitions, taxon
based and phylogeny based. I think both the idea that a species must be
one genetic unit and also that it must be monophyletic classification
wise is a great burden on systematics.

Right now there are important strictures that hobble thinking about
evolution in the systematics context. There is a general acceptance that
species are governed by the biological (genetic) species concept, and
that classification must be monophyletic. 

However, in my opinion:  A species may consist of populations that are
isolated genetically, yet in expressed traits be essentially identical.
A species may consist of populations that are tracked by neutral base
changes to reveal a different species popping off a population somewhere
in the middle of a phylogenetically complex group of populations. 

This is because of a switch in systematics from viewing expressed traits
as critical to an evolutionary classification to depending on non-coding
base changes. It's easy to use non-coding base changes. They sort of
track evolution as guessed at with morphology, they provide lots of data
that while ignoring dozens of assumptions provide statistically 100%
certainty of inferred dichotomous genealogies, throwing in the necessity
of monophyly connects non-coding base changes with classification where
previously there was none, and assuming the biological (genetic) species
concept wraps in all up in a nice package.

A paraphyletic species, in my opinion, is exactly like a paraphyletic
higher taxon, being commonly a phylogenetically complex unit most
pragmatically defined by expressed traits, and which is not changed in
any way by peripheral segregation (not necessarily isolation!) of a new
taxon. A taxonomist may choose not to split a paraphyletic species when
perceived as a single genetic unit, but split a paraphyletic higher
taxon because it is vulnerable. On the other hand, many organisms do not
fit the biological species concept. Also, there is now a tendency to
recognize fully cryptic species out of phylogenetically complex species
totally on the basis on non-coding traits alone.

******************************
Richard H. Zander 
Voice: 314-577-0276
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166-0299 USA
richard.zander at mobot.org
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For FedEx and UPS use:
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******************************
> -----Original Message-----
> From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-
> bounces at mailman.nhm.ku.edu] On Behalf Of Curtis Clark
> Sent: Monday, June 11, 2007 11:37 PM
> To: taxacom at mailman.nhm.ku.edu
> Subject: Re: [Taxacom] Invisible evolution, paraphyly
> 
> On 2007-06-11 07:58, Richard Zander wrote:
> > Maybe there's a problem with species definitions, Curtis. Could you
tell
> > us, in short, what the difference is between paraphyletic species
and
> > paraphyletic higher taxa.
> 
> Reptilia is a paraphyletic higher taxon. Its existence depends on a
> classification decision by people, not by the mode of speciation of
the
> first bird or first mammal.
> 
> Speciation by peripheral isolation ordinarily results in a
paraphyletic
> ancestral *species*. As has been pointed out repeatedly, systematists
> often disagree about the circumscription of species. But anyone who
> claims that the amniotes minus the mammals and birds constitutes a
> *single species* is clearly not using any of the plethora of
definitions
> to come out of my generation of systematists. I continue to maintain
> that anyone who uses the existence of paraphyletic species as a
> justification for the Reptilia isn't interested in evolution as a
process.
> 
> --
> Curtis Clark            http://www.csupomona.edu/~jcclark/
> Director, I&IT Web Development             +1 909 979 6371
> University Web Coordinator, Cal Poly Pomona
> 
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