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Date: Wed, 04 Feb 2004 15:01:12 +0300
From: "Igor Ya. Pavlinov" <igor_pavlinov@zmmu.msu.ru>
To: PhyloCode <phylocode@ouvaxa.cats.ohiou.edu>
Subject: Re: a comment on ancestors
>I disagree. The theoretical definition is called "definition" in it, while >the empirical definition is called "diagnosis". OK. A notion of diagnosis presumes the following: you have it explicetly formulated, take your object, compare it with characters listed in the diagnosis, and decide if it agrees or not with these characters. Suppose you formulate diagnosis of a monophyletic group as "ancestor and its descendants" - what part of this diagnosis makes you sure that your object fits this diagnosis? So, to me the matter is not very simple and straightforward and thus much interesting, because it leads to reformulation to meaning of both taxonomic definition and of diagnosis as well. ----- Original Message ----- From: David Marjanovic <david.marjanovic@gmx.at> To: PML <phylocode@ouvaxa.cats.ohiou.edu> Sent: Wednesday, February 04, 2004 2:34 PM Subject: Re: a comment on ancestors > > If you define a taxon by a character or by a type you mean that it > > is possible to allocate any newly discovered item to that taxon > > by observing respective character or type. > > This would not guarantee that the taxon would stay monophyletic -- the > character in question could have evolved by convergence. > > > The present PhyloCode definition of taxon membership > > presumes that in order to allocate a new item to one or > > another monophyletic group in existing classification, one > > has to run complete cladistic analysis in which all members > > of those groups + new item are to be included. > > Correct. Well, not necessarily all members, but some that are universally > agreed to be members of that group (such as the specifiers). > > > But what to do if those groups were recognized, say, by > > DNA analysis and no DNA data are vailable for the new item? > > :-) Make a morphological analysis for them. > This wouldn't change under an apomorphy-based definition. If > Afrotheria were defined by their unique 9 bp deletion in the gene BRCA1, and > if I wanted to find out if some Paleocene fossil was an afrothere, I'd > likewise have to make a morphological analysis of Placentalia. > > > It seems to me that theoretical and empirical definitions of taxon > > membership are mixed in the PhyloCode. > > I disagree. The theoretical definition is called "definition" in it, while > the empirical definition is called "diagnosis".