Cladistics and "Eclecticism"

[Thomas DiBenedetto]

Apologies to all those who have taken the time to respond to my posts, but
to whom I have not had a chance to respond. I seem to bump up against the
daily limit pretty quickly,,,,

-----Original Message-----
From: Richard Jensen
The branch with two terminals
                        ------B
                  ---- |
                        ------A

now has three terminals

                        ------B
                  ---- |
                        ------A
                            |
                             ---C
In my view, we have a clade with three species, two of which are as the
original
species (A,B), and a third derived from A.  There is no reason, as I see it,
for
any revision of systematic/taxonomic relationships.  B is sister to A and
its
derivatives and C is sister to A.  You are right, nothing has gone extinct.
What has happened is that a new taxon has evolved from and already existing
taxon, without altering the previously existing taxon.
...  The difference of opinion, as I see it, is that, under your view,  a
newly derived
species cannot coexist with its "ancestral" species; I believe it can.
****************
The newly derived species is composed of descendants of the ancestral
species.
It coexists with other descendants of that ancestral species.
I just dont consider one set of descendants to be identical to the ancestral
species and the other set of descendants to be different, and ranked at the
same taxonomic level as their "ancestors".
Under your system, one must abandon the notion of a taxon being defined by
the descent relationships of common ancestry. For you are excluding the new
species, but not its sisters, from the ancestral taxon. This makes no sense
under a descent criterion for taxa. Both contemporary groups are necessarily
part of the taxon originated by the ancestral "species", for they are both
descendants of that species, in exactly the same way. Thus the ancestral
group has two divergent sets of descendants, and so is a higher taxon, no
longer ranked as species.

Tom DiBenedetto