Message 2000-10-0025: Re: Hybrid specifiers

Mon, 23 Oct 2000 14:21:12 -0400

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Date: Mon, 23 Oct 2000 14:21:12 -0400
From: Kevin de Queiroz <Dequeiroz.Kevin@NMNH.SI.EDU>
Subject: Re: Hybrid specifiers

Nathan stated:

"As I understand the concept, a clade is the set of all descendents of a =
particular hypothetical species.  For this definition to be well defined =
you need a solid definition of species.  My personal belief is that there =
is no such definition."

I'm not sure how relevant this is to the issue we've been discussing, but =
I would like to know why Nathan thinks there is no good definition of the =
term "species" (since I have argued to the contrary in several papers). =

I'm also uncertain about whether Nathan ever answered my question about =
the reference of the name Alpha.  I get the impression from his last =
message that he is viewing the clade as stemming from both Y and (Z).  If =
so, he is indeed "changing what is meant by the term clade."  The =
definition of the term "clade" is a common ancestor (or ancestral species) =
and all of its descendants (not Nathan's "set of all descendants of a =
particular hypothetical species," since this definition excludes the =
ancestral species from the clade).  If this more-or-less standard =
definition is adopted, then there are two clades involved in Nathan's =
example, one stemming from Y, the other stemming from (Z), and in this =
particular case those clades are partially overlapping (have species 3 and =
4 in common).  If Nathan wants to apply a name to the combination of these =
two clades, that's OK, but we probably should call it something other than =
a clade (such as a set of two partially overlapping clades).  =20

It also occured to me that under one of the ways of stating a node-based =
definition, the application of the name might not be ambiguous even in =
this confusing case.  That is, if Alpha is defined as the clade stemming =
from the most recent common ancestor of 3 and 4 (as opposed to the least =
inclusive clade containing 3 and 4), then unless the splits at Y and (Z) =
occurred at the same instant (highly unlikely), one of the ancestors (Y or =
(Z)) is more recent than the other, and thus the name refers to only one =
of the two clades (though in practice it might not be easy to determine =
which one).

20 Oct 2000


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