Message 2002-02-0008: Re: interesting style of definition

Fri, 15 Feb 2002 12:11:10 +0100

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Date: Fri, 15 Feb 2002 12:11:10 +0100
From: Mieczyslaw Wolsan <wolsan@twarda.pan.pl>
To: PhyloCode@ouvaxa.cats.ohiou.edu, phyloadvisors@ouvaxa.cats.ohiou.edu
Subject: Re: interesting style of definition

Sorry, there was a problem with my previous posting. Now it's ok (I hope).

1) "extant"

This problem has already been addressed comprehensively in the literature 
(see, e.g., Bryant 1996, Syst. Biol. 45: 174-189).

2) "stemming"

If clade A stems from B, is it necessary for clade A to contain B? I feel 
it is not. And this is my point. Of course, a clade consists of an ancestor 
and all its descendants. The problem I find with the discussed definition 
is that it is not clear (for me) whether the specified "last common 
ancestor" is contained in the clade. If I correctly recognize the meaning 
of the word "stemming" , the phrasing "clade A stemming from B" referes to 
two different clades: one containing B, and the other without B.

3) "ancestor"

There has been much discussion related to the problem, also on the list 
(recently by Kevin de Queiroz, as far as I remember). The draft PhyloCode 
defines the term "clade" as "a group of species comprising a common 
ancestor and all of its descendants". (I would say "a group of lineages" 
and would replace the word "comprising" by "composed of" because I feel the 
word "comprise" meant to contain or include, but not to constitute or to 
compose.) I think that the majority of systematists agree with the draft 
PhyloCode's definition. However, I do not think that according to this 
definition it is necessary for the ancestor to be a species. I think many 
systematists agree that it is not necessary for a clade to begin with a 
complete species. If one wishes to have a species as an ancestor, this 
should be explicitly stated in the definition.

Mieczyslaw

Mieczyslaw Wolsan
Professor and Chair
Department of Vertebrate Paleontology
Institute of Paleobiology
Polish Academy of Sciences
Twarda 51/55
00-818 Warszawa, Poland
Phone: +48-22-697-8793
Fax: +48-22-620-6225
E-mail: wolsan@twarda.pan.pl
http://www.paleo.pan.pl


  

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