paraphyly

Tom DiBenedetto tdib at UMICH.EDU
Fri Jun 13 10:23:14 CDT 1997


On Thu, 12 Jun 1997 15:37:28 -0500, Thomas G. Lammers wrote:

> Monophyly in the strict cladistic sense (i.e.,
>holophyly) is as unobtainable as  perfection.  It simply does not exist nor
>endure in the real world.   To insist that our system of nomenclature
>reflect a condition that seldom obtains in reality, now THAT is REAL nonsense!

I think this represents a conception of monophyly which is very
different from my understanding. Perhaps the problem is the comlexity
of meaning and association by which the word is understood (similar
in a sense to the "species" problem). Monophyly. paraphyly. and
polyphyly are characterisitics of *groups conceived by humans*. and
refer (following Hennig, who formulated the distinctions) to groups
which are defined around apomorphies, plesiomorphies, and
convergences respectivly. The expected *result* (given our
assumptions) of constructing groups under such criterea is to have
groups which include all descendants of a
common ancestor, some descendants of a commn ancestor, or
"descendants" which do not share a common ancestor, respectivly. Of
course, one must be prepared to accept that it is possible to learn
about history from the study of character distribution in order to
make that step, but if you cant do that, then you probably are not
interested in classifications that seek to represent history.
        To claim that monophyly is "as unobtainable as perfection" is
to claim, essentially, that it is impossible to recognize groups on
the basis
of apomorphies, which is clearly not the case. Although you may be
wrong in your assesment of whether a character truly is an apomorphy,
you need not be. To claim that monophyly "does not endure in the real
world" strikes me as deeply odd. The point of using a criterion of
apomorphy by which to recognize groups is that we (all?) assume that
there really are such things as homologies, and that by recognizing
them at their proper level of generality, we are discovering groups
which have real historical identities. We have defined many
monophyletic groups for which there seems little doubt that they
represent real historical lineage-branches.


Tom
DiBenedetto                     http://www-personal.umich.edu/~tdib
/
Fish Division                                   tdib at umich.edu
University of Michigan Museum of Zoology




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