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Date: Thu, 28 Sep 2000 09:54:44 -0700 (PDT)
From: Nathan Wilson <velosa@cinenet.net>
To: PhyloCode@ouvaxa.cats.ohiou.edu
Cc: "Moore, Gerry" <gerrymoore@bbg.org>, 'Philip Cantino' <cantino@ohiou.edu>
Subject: RE: Nathan Wilson's question
Philip Cantino wrote: > Nathan is concerned about the effect of interclade genetic transfer on > clade nomenclature. Actually my concern is a deeper than that. My real concern is that the definitions of the PhyloCode depend on the concept of a species. While the concept of species is a useful method of simplifying the natural world, it is ultimately a fiction. The definitions of species are many and varied and almost all of these definitions have some merit in terms of usefulness, but for each of these definitions there are grey areas and exceptions. Fundamentally, this is because there is nothing about the evolutionary process that *necessitates* speciation. The fact that it happens is interesting and has profound effects on the results of evolution, but making our description of the process depend on such an arbitrary emmergent property will necessarily result in poor definitions much like the problems in traditional nomenclature. The interesting thing is that a relatively slight adjustment in one of the definitions of clade makes it totally independent of the concept of species. As defined now the node-based clade definition makes the assumption that there is a single most common ancestor to the entities chosen to define the clade. What is the nature of that ancestor? Is it another clade? Is it a species? Is it an individual? Clearly it can't be another clade. If it is taken to be a species that necessitates a clear definition of species which I sincerely doubt exists. Taking it to be a single individual makes a very strong assumption about the evolutionary process which I doubt anyone would want to make. On the other hand, if you expand the definition to allow for multiple common ancestors that are all individuals you get a far cleaner definition. The nice thing is that the larger clades that we all know and love remain unchanged. The common ancestors for such groups will all be from the hypothesized original species (if one exists). Gerry Moore also brings up an interesting point about using members of non-nested clades as specifiers, but I think the example he gave doesn't quite make the point. As Philip Cantino points out there is no problem under the current definitions if one of the two species belongs to two non-nested clades. However, there is a problem if both species belong to the same two non-nested clades. If that's the case then a node-based clade defined using those two species has no clear definition since there are now multiple most recent ancestors and no clear way to choose between them. Nathan Wilson Computer Scientist Collective Source nathan@collectivesource.com