Message 2001-09-0002: Re: Apomorphy-based definitions

Thu, 23 Aug 2001 15:00:25 -0400 (EDT)

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Date: Thu, 23 Aug 2001 15:00:25 -0400 (EDT)
From: "T. Mike Keesey" <>
To: David Marjanovic <>
Cc: PhyloCode mailing list <>, Mike Taylor <>
Subject: Re: Apomorphy-based definitions

On Thu, 23 Aug 2001, David Marjanovic wrote:

> Coming to think of it, apomorphy-based definitions _are_ circular, aren't
> they?

How are they circular?

Organism X has character A. Organism X has ancestors with character A,
which is how it inherited character A. Somewhere along the line, one of
its ancestors (a mutant) was the first to possess character A.
Clade(A in X), therefore, is that ancestor and all of its descendants. I
don't see any circularity.

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.

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