cladism's greatest weakness

John Trueman trueman at RSBS.ANU.EDU.AU
Thu Sep 23 10:20:42 CDT 1999

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

John T.

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

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

More information about the Taxacom mailing list