cladism's greatest weakness

[John Trueman]

Richard Jensen wrote:
X retains all the properties that allow us to
>recognize it as X.  Y has some new property that makes it reproductively
>isolated from X.  Given that this reproductive isolation exists, we have
>every reason to suspect that X and Y are evolving separately.  The fact
>that X is unchanged does not prevent our recognition of X as a distinct
>entity different from Y; after all, Y has a unique character (call it
>anything you like (I'll call it A') that allows
>us to recognize it as different from X. This would be a case where the
>"absence of something" allows us to recognize that one taxon (X) is
>different from another taxon (Y). My key to the two taxa would simply have
>a couplet
>
>        A' present..........Y
>        A' absent ..........X

Going back to my earlier comment re paraphyly, X is identifiable only as
that part of X+Y which does not have A'. In other words it is identifiable
by plesiomorphies alone. Is there any reason it should not be considered
paraphyletic?

John T.

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John Trueman
Faculties Research Fellow
Bioinformatics Group
Research School of Biological Sciences
Australian National University
Canberra, ACT 0200,  AUSTRALIA


ph: +61 2 6249 4840
fax: +61 2 6279 8525
email: trueman at rsbs.anu.edu.au

Reason is a tool. Try to remember where you left it.
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