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Re: Re: Linnean Classification and Creationism



>Tom Holtz writes:
>
>"All monophyletic taxa are real taxa, if we accept that evolution
>by descent has occurred... As such, monophyletic lineages exist,
>and thus clades exist."
>
>I have a problem with the word "exist," which was first brought
>home to me when I discussed the idea of "species" with a cladist
>(before my boycott of the sci.bio.paleontology newsgroup). I
>explained that any species that is ancestral to any other species
>is by definition a paraphyletic taxon, because it no longer
>includes all its descendants, and that for cladists to allow
>species, but not other taxa, to speciate is inconsistent.

Species are a fundamentally different type of taxon than a clade.  Species
are not clades (except under the phylogenetic species concept).  Species can
be defined under any number of concepts, of which the "biological" species
and the Specific Mate Recognition System concept make the most sense to me.
Species are a population of interbreeding organisms with viable offspring:
monophyly is not required by the definition.  When a subpopulation diverges
so that it is incapable of having viable offspring with the ancestral
population, that subpopulation is a new species.

Monophyly is not a requirement of species (and ONLY species) within most
cladistic taxonomies (or, indeed, any other system of taxonomy).

> He
>explained that when a species speciates, it "ceases to exist,"
>and is thus not a paraphyletic taxon. So, for example, when a new
>species B "buds off" as a subpopulation of species A, species A
>vanishes (just like that!) and is replaced by species B and a new
>species, C, which holds all those descendants of A that are not
>in B.
>
>(No--I'm serious! This is how he said it!!)

This person is unfamiliar with species definitions, it seems, or requires
the phylogenetic species concept, something many cladists do not require.
Read almost any recent multiauthor book on species concepts for further
clarification (there have been several in recent years).

>Well, if the species "ceases to exist," what meaning does this
>have for the clade that comprises the descendants of that no-
>longer-existing species? It would seem, from the foregoing, that
>the only parts of any clade that "exist" are the terminal taxa,
>and that most of the clade therefore does not "exist."

Since clades are DEFINED (<- note this word) as a species and all its
descendants, it cannot, by DEFINITION, "cease to exist" until all
descendants of the ancestor go extinct.

Clearly EVERY SINGLE GODDAMN DESCENDANT of that ancestor existed (was extant
in physical reality).  How do you not see this?  Inquiring minds want to know. 

>Cladists seem to use the word "exist," to suit their purposes,
>_very_ freely indeed.

And other people use taxonomy to suit their purposes, _VERY_ freely indeed!
:-)

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084