Message 2000-09-0006: RE: Nathan Wilson's question

Thu, 28 Sep 2000 09:54:44 -0700 (PDT)

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Date: Thu, 28 Sep 2000 09:54:44 -0700 (PDT)
From: Nathan Wilson <>
Cc: "Moore, Gerry" <>, 'Philip Cantino' <>
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

Nathan Wilson
Computer Scientist
Collective Source


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