Farewell to Species - reticulation

[Thomas DiBenedetto]

I said:
>My view of a taxon is that it represents a lineage (branch, or
>system of branches)emanating from a common ancestor. The original taxon
>still exists, and will continue to exist until all of its descendants are
>extinct. The original taxon is, however, more complex than a simple
lineage
>branch; that original single branch has given off a sublineage. [...]
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And Curtis Clark responds:

>From a genetic standpoint, this is ludicrous. In many groups (e.g. annual
plants), species form peripheral isolates all the time. Only occasionally
do these become new species.
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I dont understand what you find to be ludicrous though. Obviously species
give off isolates all the time, only some of which become new "species". If
they dont become new species, then what is the issue? They wont be seen and
recognized and nothing will change taxonomically. They will just be isolated
populations that sputter out.
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C.C.:
To suggest that a taxonomic system should
treat the ancestral species differently depending on whether peripatric
speciation succeeded or failed effectively removes the system from the
realm of real-world events.
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I dont follow. Whether or not speciation succeeds seems to me to be very
much a real-world consideration. If we are erecting a taxonomy based on the
real history of lineages, then the question of whether a lineage has in fact
divereged seems to be absolutely a relevant concern.
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C.C.:
I'm no anti-cladist (Kinman has accused me of
being a radical cladist), and I am a firm advocate of monophyletic higher
taxa, but IMO shoehorning observed biology into a system that misrepresents
it is on a par with accepting paraphyletic groups just because they are
"grades".
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I guess I agree that shoehorning observed biology into a system that
misrepresents it, is a very bad thing. I was not aware that that is what I
was doing. And I still dont see how I am.
Quite simply, for me, a taxon is a monophyletic group (ancestor and all
descendants). If some of the descendants of a particiular ancestor diverge
from other descendants, how is it misrepresenting reality if I insist that
they all are still descendants of that ancestor? The name adheres to the
ancestor and all of its descendants. Both subgroups should bear the name. I
dont understand the basis for your disagreement.

Tom DiBenedetto
tdib at dccmc.org