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Re: Species [ was: Re: Hadrosaur nomenclature]
On Thu, Oct 18, 2001 at 12:14:07PM -0500, Jonathan R. Wagner scripsit:
> As for conserving the binomial as a convenience, I must disagree
> wholeheartedly. Our nomenclature should refer to real entities *only*. If I
> believed that species or genera are not real, I feel it would be my duty to
> abandon both (as some have suggested). Genera aren't real by anyone's
> metric. We should chuck the idea along with all other categorical ranks.
Well, that's well argued, but I disagree with you anyway.
A species is a population where there is no genetic restriction to the
degree of the common descent among the next generation from any member
of the species -- they can all mate effectively with each other, given
the opportunity. (and yes, I know about the circumpolar gulls and the
hybrid frogs; this sort of definition still works if you're willing to
restrict the species concept to populations of genes, rather than
morphology. I think that's the right thing to do, in principle, since
the genes are what's determining morphology and any given morphology can
be reached in more than one way.)
That's like slicing through a tree and you get a round shape; the tree
of life is going into the future in one direction there.
A genus can be thought of -- and I do not claim always, or even often,
thought of, but *can* be thought of -- as the slice just up from the
fork of the tree, where the gap isn't large enough to have admitted
another branch of the tree. 
Since it's rare -- not unknown, but certainly rare -- to have a
statistical universe of dinosaur specimens, it's really hard to decide
if what you're looking at is a species or a genus; are these differences
big enough differences to indicate two populations that are the mutal
product of a recent interbreeding population without any intervening
For paleontology, I think the awareness that that isn't always an
answerable question is a very good thing, since insisting on 'species'
runs one much harder into the data hole caused by insufficent observed
 Yes, I know this is inadequate to the cases; the proper way to think
about this is the count of intervening non-interbreeding populations
from the common ancestral interbreeding population; the species for
whom that count is 1 form a genus.
To maintain the end is to uphold the means.