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Re: Cladistics question (and Re: Evolutionary taxonomy)

Rob Meyerson wrote:
>Subject: Evolutionary taxonomy
        Actually, I'm not sure your question itself should touch off a
"clade war".  It is a valid question for anyone who uses cladistic analysis,
which includes followers of Evolutionary Systematics as well as followers of
Phylogenetic Systematics.
        "Evolutionary Taxonomy" is the appelation bestowed upon the modern
interpretation of Linnean [sic?...too early in the morning...] systematics
by the practitioners of that mystical art. It would be more appropriate to
file this question under "Subject: Systematics". I think that by doing this
you will avoid a starting a clade war unintentionally.
        Hopefully one of the real cladists on the list can actually *answer*
your question.  :)

>Believe me, I am not trying to reflame the Clade Wars.  I simply wish to
>understand the dynamics of how Cladistics work.
        "General Hennig, years ago you helped my father in the Clade Wars..."

Jeff Poling wrote:
>   Let's say we have hypothetical clades A and B,[...].
>... Clade B can be diagnosed using the blue button character because all Bs
>have blues, yes?  Can Clade A be diagnosed using green buttons even though Bs 
>have blues (assuming all animals outside of A have red buttons)?
        If your analysis confirms it, you could say that the primitive state
for clade A is green buttons. I guess you could diagnose B this as having
blue buttons.  But recall that this does not mean that you should *define* B
as all critters with blue buttons.  Diagnosis != definition in P.T. 
        Note also that diagnosis is not an effective means of producing a
pylogenetic hypothesis, as the addition of a new taxon may change the
distribution of "diagnostic" characters.

>   Also, someone recently mentioned a stem vs. a node based clade.  Wot's
>the difference?
        Node-based: a taxon composed of the most recent common ancestor of
two or more terminal taxa and all of its decendants.
        Stem-based: a taxon composed of all animals more closely related to
one terminal taxon than to one or more other terminal taxa.

| Jonathan R. Wagner                    "You can clade if you want to,     |
| Department of Geosciences              You can leave your friends behind |
| Texas Tech University                  Because your friends don't clade  |
| Lubbock, TX 79409                               and if they don't clade, |
|       *** wagner@ttu.edu ***           Then they're no friends of mine." |
|           Web Page:  http://faraday.clas.virginia.edu/~jrw6f             |