[Previous by date - RE: Art 10.1]
[Next by date - Re: Stem-based taxon definitions]
[Previous by subject - Re: Stem-based taxon definitions]
[Next by subject - Re: Stem-based taxon definitions]
Date: Mon, 31 Jul 2000 15:35:01 -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 11:40 AM 7/31/00 -0400, Dr. de Queiroz wrote: >KdQ: >This is irrelevant. Every group is going to be paraphyletic or >polyphyletic at some level, If you believe that para- and polyphyletic describe the inclusion or exclusion of SPECIES, not of individuals, then this is not necessary. It is very easy to conceive of an entirely monophyletic group of SPECIES, even if this is a para- or polyphyletic group of ORGANISMS. Just as an organism can be a paraphyletic assemblege of cells, so can a species be a paraphyletic assembly of organisms. If I assert that a clade is a species and all of its descendants, then that clade is purely monophyletic with respect to species, since it contains an ancestral species and all of its descendant species. This is a consequence of species reality. I species are real entities which produce new species, then we can talk about, and recognize, para-, poly- and monophyletic groups of species. If species are real, then a monophyletic group of species is as real as a monophyletic group of organisms. Indeed, it is somewhat easier to concieve of since, for the most part, species are not biparental. DNA does not reproduce cells, cells produce cells. Cells do not produce organisms, organisms produce organisms. Organisms may found species, and a single organism may perhaps be part of a species unto itself, but an organism never IS a species, and it never SPAWNS a species. A clade, as a real entity (rather than just a collective), is similarly begun by a species (the ancestral species), but that species is never the clade and vice versa (a consequence of this, however, is that there *can* be a monospecific clade). Following this line of reasoning, clades are never polyphyletic or paraphyletic... this is a tautological property of monophyletic groups. A clade might be polyphyletic with respect to organisms, but again, not with respect to species, just as a clan may be monophyletic with respect to individuals, but paraphyletic with respect to cells. Am I just way off base here? >and no one (except perhaps Baum and Shaw) seems >to have a problem with the idea that species (and thus the clades derived >from them) are paraphyletic or polyphyletic in terms of their component >organisms, cells, or genes. I accept this as necessary and evident. Hoewever, this does NOT require clades to be para or polyphyletic with respect to species. >See the discussion of phyly in my 1999 paper >(in Species: New Interdisciplinary Essays). I shall reread this as soon as I have time. >Moreover, I didn't advocate >changing the phrasing to "ancestral individual." The solution is to leave >the type of ancestor unspecified, thus allowing the ancestor to be part of a >species (the part that's more closely related to A than to B; this is the >relevance of the paper by de Queiroz and Donoghue, 1988). But then, what sort of common ancestor does a biparental species have? it will have a different most recent common ancestor depending on whether you follow the male or female line, won't it? I find it much easier to deal with ancestral species than ancestors, even if it is just evading the question. >On the other hand, the problem you raised with the wording of stem-based >definitions is based on a wording not used in the PhyloCode. You stated the True enough. >phrasing as "species A and all species sharing a more recent common >ancestral species with A than with B." This is not the wording used in the >PhyloCode, which states the definition as follows: "Y and all oganisms [not >species] that share a more recent common ancestor [not ancestral species] >with Y than with W." But a group of organisms is a clan or a clone, not a clade. Will we be naming clans and clones under the phylocode? >The wording >actually used in the PhyloCode wouldn't result in a reference to a >polyphyletic taxon. Take the same example, but pretend A-G are organisms. > > A D' > D > D E > D F' > F F' > FF' B > F GB > C G > CG > C "individual A and all organisms that share a more recent common ancestor with A than with B." Organism F' shares a MRC with A (i.e., F) than it does with B. Organism F's most recent ancestor is C, which is also ancestral to B. Therefore, it appears to me that the Phylocode wording does indeed result in a polyphyletic group of organisms. Am I in error? You could, alternately, take an ultra-Hennigian approach, and declare that the part of F after the spawning of F' (the part of my mom which exists after 1973, in human terms) is separate, and consists of cells closer to A than to B. This, to my mind, is analogous to cutting clades across species lines. I favor clades which are monophyletic groups of (real) species, not organisms. As such, they do not cut species lines. 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