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Date: Thu, 19 Oct 2000 11:24:03 -0400
From: Kevin de Queiroz <Dequeiroz.Kevin@NMNH.SI.EDU>
To: PhyloCode@ouvaxa.cats.ohiou.edu
Subject: Hybrid specifiers
Just a couple of comments on Nathan and Gerry's recent postings:
First, I like Nathan's analysis of the different implicit definitions =
underlying Gerry's and my interpretations. The perspective of a computer =
scientist is quite useful. In this context, the only problem I now have =
with Gerry's interpretation is calling the ancestor of the more inclusive =
clade in the example "the most recent common ancestor." I would prefer a =
different term, perhaps something like "most recent complete ancestor." =
Thus, potential nomenclatural ambiguities resulting from the different =
interpretations could be solved by adopting definitions that distinguish =
between these two classes of ancestors.
Second, I agree with both Gerry and Nathan that the example involving =
multiple hybird specifiers creates more serious ambiguities (i.e., ones =
that cannot be solved simply by recognizing different classes of ancestors)=
. That is to say, I also agree with Gerry that when the clades in =
question are non-nested, we should not use numbers of subtaxa (e.g., =
included species) to consider one of the clades more or less inclusive =
than the other. In cases of this kind, Michel's solution of emending the =
definition through conservation seems appropriate.
One thing that puzzles me is Nathan's suggestion "to allow for multiple =
most recent common ancestors in node-based clades." First, I'm unclear on =
which ancestors he has in mind in the example--Y and (Z) or Y, (Z), and Z. =
Second (and more importantly), regardless of which ancestors he has in =
mind, I'm unclear on what he means by allowing multiple ancestors. Would =
the name ("Alpha," to use Gerry's example) be applied (separately) to =
clades stemming from two or more different ancestors (e.g., Y and (Z))? =
Or would it be applied to a group composed the clades stemming from those =
different ancestors? Neither of these alternatives seems desirable to me. =
The first results in ambiguity, the second is potentially confusing in =
applying the name not to a clade but to a set of clades. =20
Kevin
19 Oct 2000