Cladistics and "Eclecticism"

[Richard Jensen]

I can't let this pass without comment, despite Tom's request.

Thomas DiBenedetto wrote:

> -----Original Message-----
> From: Richard Jensen
> >                         ------B
> >                   ---- |
> >                         ------A
> >                             |
> >                              ---C
>
> Since we're getting into improbable, but certainly not impossible, examples,
> let's consider this.  In my example above, the isolated population (C) is
> the
> result of autopolyploidy with a single propagule getting established and
> founding the new population.  C has both morphological apomorphies
> (polyploidy
> often yields these) and is a "good" biological species.  A, as a
> species-level
> taxon, no longer exists.  So, we now have two species and let's suppose that
> for
> the next two centuries C and A undergo separate evolutionary fates.
> ************
> You are confusing me here. You said "A, as a species level taxon no longer
> exists". And then for the rest of your message you speak of A as a species.
> I would say that A is a higher taxon. So lets give the name D to the
> persistent sister of C.

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.

>
> ************
> The
> population of C begins to spread locally and some additional genetic
> apomorphies
> evolve.  On the other hand, during the same time A {D} experiences
> stabilizing
> selection that results in no apomorphies that could be used to differentiate
> extant A  {D} from A of 200 years ago.  Then, the habitat in which C is
> surviving
> (ANWR?) is destroyed and C becomes extinct.  What is A {D} now that C is
> extinct?
> With no apomorphies to differemtiate it from its ancestor (pre-C A), it's
> still
> A.  Would this be a case of extinction (as a taxon) not being forever?
> **************
> What do you mean "extinction not being for ever"? _Nothing_ went extinct in
> the first place!

I asked a question, I did not make a claim.  But, you made A "extinct" as a
species level taxon by changing its name to D (see below).  That's the point I
am making - A, as a species level taxon, is no longer recognized (hence
extinct).

>
> If C now goes extinct, and we never had or ever will have evidence of its
> existence, then we would never have recognized D, and we would always call
> the persistent species A. I am sure that there are millions of little
> branches in history that have went extinct without a trace, and that we will
> never know about.
> If we had seen this whole story transpire, as we here laid it out, then I
> guess we could continue to recognize D as a descendant of A, and C as an
> extinct descendant of A. The lack of character evidence for D, as opposed to
> A, would normally not allow us to recognize D, but given our special
> knowledge of what actually happened, we could recognize it none the less.
> Character evidence is just that - evidence to support an inference of what
> actually happened. It is what actually happened that should be the ultimate
> criterion.
> May I suggest that instead of coming up with ever more complicated scenarios
> for me to deal with, that you join the effort? The principle is simple: lets
> try to make our naming system conform to the real history of lineages.
>
> Tom DiBenedetto

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. Yes, what I have
described is an extreme case of "punctuated equilibrium;"  but something like
this could happen and be noted and documented by systematists.  It may be
happening right now.  I argue that 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.

Dick

--
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