Cladistics and "Eclecticism"
rjensen at SAINTMARYS.EDU
Thu Feb 7 10:10:41 CST 2002
Thomas DiBenedetto wrote:
> -----Original Message-----
> From: Richard Jensen
> Each letter refers to a single a single ancestor-descendant lineage. In my
> view, A continues as a species because it is, in fact, the same thing.
> But that is clearly not the case. How can you call A a single
> ancestor-descendant lineage when it has C budding off the side of it?
> Clearly A is NOT a single lineage - it is a branched lineage; a higher
> ... you made A "extinct" as a
> species level taxon by changing its name to D (see below). That's the point
> am making - A, as a species level taxon, is no longer recognized (hence
> How many times do I have to say this? "Extinction" is a totally ridiculous
> way of characterizing the simple FACT that A has evolved from being an
> unbranched lineage (hence ranked as a species) to a being a branched lineage
> (hence a higher taxon).
I hate to continue this, but how many times do I have to say this: As a species
level taxon, A no longer exists. It's obsolent, it's invalid, call it what you
will. As soon as you redesignate my original species A (a single lineage that
is distinct from its sister species B) as a higher level taxon, it is no longer
a species! If you want to quibble over a minor sematntic point, ok. But if you
continue to argue as if what you are doing is not equivalent to "nomenclatural
extinction" (choose your own word), then you are simply being obfuscatory.
After all, you're the one who said that we would now rename A (to D) to
differentiate it from C as well as from the common ancestor (A) of D and C
> My point is that I don't believe that species A must be renamed in order to
> acknowledge the fact that species C is derived from species A.
> TAXON A is not renamed at all. Its rank is merely adjusted to reflect the
> reality that it is now branched.
> I sense you are totally conflating an ecological sense of "species" with the
> systematic sense of species as taxa.
As noted above, see your earlier posting. You have changed the rank of A (and
indicated it should be renamed) - it is no longer a species rank taxon!
And, ecological versus systematic usages are not the issue here (it seems to me
you keep throwing this in as a red herring). Species do exist as ecological
entities, but I am using my concept of species in a strictly systematic context
for this discussion.
> ..... there is no need, under such circumstance, to
> rename species A - it has not changed in any way except that it is the
> progenitor of another species.
> Once agian, "species A" as some sort of an ecological unit may look the
> same, but the reality of the lineage relationships are different. Yesterday
> the lineage was terminal - a species. Today it is branched, a higher taxon.
> It (the original lineage) is still called A. Its rank has changed however.
So, as you note above, A is no longer a species ("Its rank has changed..."),
which is the point I have been making.
If we have an evolutionary entity, A, that is recognizable (by whatever
criteria), and it undergoes stabilizing selection for some length of time, what
we have at the end is the same thing, no matter how many peripheral populations
have become isolated. To claim that it is something else, is to claim that
anytime an individual with a unique genome leaves the lineage, the lineage has
changed. I don't think anyone wants to be that extreme. What happens to A as a
lineage is independent of what happens to the new isolated population (C), and
the relationship between A and B has not changed: they are still sister species.
I maintain, as a systematist, that in my scenario there are now three species,
two of which continue just as they had before C became isolated. Nothing
prevents us from recognizing the historical relationships among these three
species and no changes in rank are necessary to allow us to have a system of
classification that works.
Richard J. Jensen TEL: 219-284-4674
Department of Biology FAX: 219-284-4716
Saint Mary's College E-mail: rjensen at saintmarys.edu
Notre Dame, IN 46556 http://www.saintmarys.edu/~rjensen
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