Message 2001-09-0007: Re: Apomorphy-based definitions

Fri, 24 Aug 2001 12:45:58 -0300 (ADT)

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Date: Fri, 24 Aug 2001 12:45:58 -0300 (ADT)
From: "Alastair G. B. Simpson" <>
To: David Marjanovic <>
Cc: PhyloCode mailing list <>
Subject: Re: Apomorphy-based definitions

> Now there IS another glaring problem. Characters do not, typically,
> suddenly emerge fully-formed, but, rather, develop in tiny
> increments. So defining a certain trait should be EXTREMELY specific,
> and even then it may be prone to complications.

Okay, so there is a devil-in-the-detail of apomorphy-based
definitions (when does a feather become a feather? and therefore, if I
have a 'borderline feather', am I in Aves or not?*):  However, there is
presumably a similar finest-scale fuzziness in determining membership in
stem- and node- defined taxa too (especially, but not solely, in
non-clonal lineages), so I don't think this 'problem' with apomorphy-based
definitions should be invoked as a reason to prefer stem- or node-
definitions over apomorphy-based ones.

*carrying on our example where 'feathers homologous to those in Passer' 
are taken to define Aves.

Alastair G.B. Simpson, PhD
Laboratories of Andrew Roger and Ford Doolittle,
Department of Biochemistry and Molecular Biology,
Room 8B, Sir Charles Tupper Medical Building,
Dalhousie University, Halifax, Nova Scotia,
B3H 4H7, Canada.

Phone: 902 494 2881 (Country code 1)
  Fax: 902 494 1355 (Country code 1)


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