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Date: Sat, 29 Jul 2000 18:49:12 -0500 (CDT)
From: "Jonathan R. Wagner" <znc14@TTACS.TTU.EDU>
To: Kevin de Queiroz <Dequeiroz.Kevin@NMNH.SI.EDU>
Cc: PhyloCode@ouvaxa.cats.ohiou.edu
Subject: Re: Stem-based taxon definitions
At 12:13 PM 7/29/00 -0400, Dr. de Queiroz wrote:
>Jonathan R. Wagner wrote:
>
>>This [wording] avoids the problem of potential polyphyly in the
>traditional "X and all taxa sharing a more recent common ancestor with X
>than with Y" phrasing, as well as avoids the slight ambiguity I see in
>formulations involving the phrase "the most inclusive clade."
>
>Perhaps I missed something. I don't see how the first phrasing could end
>up causing a name to be associated with a polyphyletic taxon,
In a posting dated 6/1/00, I wrote:
" Indeed, there is (as far as I can see), a much more grave potential
problem with the first definitional format. Consider the following species
phylogeny (using the same species discussed previously, where each letter is
a species):
A D'
D
D E
D F'
F F'
FF' B
F GB
C G
CG
C
(read as: "species A is sister to species D', both descended from
species D, species D is descended from species F, as is species F'. both
species F and species G are descendants of species G, and species B is a
descendant of species G.)
Clade X is defined as "species A and all species sharing a more
recent common ancestral species with A than with B." Species A, D', D, E,
and F' all share a more recent common ancestral species with species A than
with species B. However, species F does not. The most recent ancestral
species of species F is species C, which is also ancestral to species B.
Therefore species F is not included in the taxon. The result is a
polyphyletic group."
>nor do I see any ambiguity with the seond phrasing.
Please see the discussion between Dr. Wolsan and I, in which part of
his point was that referencing a "CLADE" as opposed to "an ancestor and all
of its descendants" or "and ancestral species and all of its descendants"
allows one to separately define what you consider a clade to be (e.g., a
species and all of its descendants vs. a breeding pair and all of its
descendants). The result is that the group identified by the definition then
changes based on different interpretations of the word clade. This is an
ambiguity which I do not find helpful, since I think you will agree that a
breeding pair and all of its descendant organisms is a different group than
a species and all of its descendant species. I want my Lepidoptera to be the
same as everyone else's lepidoptera... isn't that the point, after all?
Personally, I prefer to have it spelled out: "an ancestral species and all
of its descendants." No ifs, ands, or buts that I can see in that.
>I can imagine that there could be
>problems with either of these types of wordings if there are problems with
>the specifiers (X and Y in the examples), but these problems would also seem
>to apply to Wagner's proposed alternative phrasing.
Certainly.
Wagner
--------------------------------------------------------------------------------
Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
"Why do I sense we've picked up another pathetic lifeform?" - Obi-Wan Kenobi