[Previous by date - Re: interesting style of definition]
[Next by date - Re: interesting style of definition]
[Previous by subject - Re: interesting style of definition]
[Next by subject - Re: interesting style of definition]
Date: Fri, 15 Feb 2002 12:07:40 +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
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 2) [Does this include the ancestor?] The wording related by Mike Keesey is perhaps cumbersome, but it does explicitly include the ancestor: "the CLADE stemming from the... ancestor..." where a "clade" is defined as an ancestor and all of its descendants. > I think it does. PhyloCode uses that word, doesn't it? In deed it does. (see www.phylocode.org <Glossary>) clade: "One of the two kinds of biological entities whose names are governed by this code; a group of species comprising a common ancestor and all of its descendants." Richard Swigart There are at least three problems with this definition. First, the clade referred to by the definition changes with the extinction of taxa; and this is the most serious problem. Second, it is not clear whether "the last common ancestor" is contained in the clade or not (as a non-native English speaker I cannot evaluate this properly, but I do not think that the word "stemming" specifies this unambiguously). Third, "the last common ancestor" may refer to either a species or a population, or a breeding pair, individual organism, etc.; in each instance, we have to do with a different clade. This might seem like extreme pedantry, but if explicitness in phylogenetic nomenclature is important, this should be reflected in the wording of phylogenetic definitions. 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