Message 2001-02-0010: Re: apomorphy-based names

Tue, 06 Feb 2001 09:18:26 -0500

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Date: Tue, 06 Feb 2001 09:18:26 -0500
From: david baum <>
Subject: Re: apomorphy-based names

I just wanted to endorse David Hillis' criticism of apomorphy-based names:
namely that it is pretty much impossible to provide an unambiguous
definition of any apomorphy that would adjudicate cases in which future
taxa are found to have intermediate conditions.  Additionally, if there
were no apomorphy-based names the phylocode would have added value because
one could query the Phylogenetic Nomenclature database with a tree and get
back the correct name for each named clade.  I believe that this
bioinformatic advantage could be the key to convincing the broader
biological community that the PhyloCode is the way to go.

at the same time, I remain unconvinced that, as Kevin put it, "....
sometimes an apomorphy-based definition is the appropriate definition for
the clade concept being named."  A good synapomorphy certainly can provide
good evidence that one has identified a clade, and can be immensely useful
when communicating the identity of a clade to somebody.  However, I cannot
see why it would ever be the appropriate DEFINITION of a clade concept.
What is to stop you aiming for a stem-based or node based definition, even
a conservative one listing lots of specifiers?

Consequently I disagree with Jonathan Wagner's recommendation that "clade
names derived from apomorphy names be given apomorphy-based definitions."
If the apomorphy is a strong one then the clade is strong in which case one
can always find some conservative stem-based or node-based definition that
will accurately point to the clade of interest.  And if, down-the-road, the
name no longer applies to the clade for which the character is apomorphic -
so be it.  Systematists are very good at not reading too much into the
literal meaning of names.

David may be right that for internal political reasons we cannot yet ban
apomorphy-based definitions.  But I hope that one day the vertebrate
paeontological types, and whoever else is inclined towards apomorphy-based
definitions, can be convinced to make-do with stem-based and node-based


P.S.  I think "node-based," "stem-based," and "apomorphy-based" should be
in the PhyloCode glossary

David Baum
Dept. Organismic and Evolutionary Biology
Harvard University Herbaria
22 Divinity Avenue
Cambridge MA 02138

Tel: (617)496-6744, -8766
Fax: (617)495-9484


Feedback to <> is welcome!