an answer to paraphyly

Tom DiBenedetto tdib at UMICH.EDU
Mon Jun 16 12:33:44 CDT 1997


On Sun, 15 Jun 1997 10:08:53 EDT, Robin Panza wrote:

>>As far as I understand it, after a speciation event, two entirely new taxa
>>are described, if such an event could be witnessed. The "old" species they
>>evolved from ceases to exist as far as cladistic methodology is concerned.
>                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>Ah, but that's the point!  It has nothing to do with nature, just a byproduct
>of a theory that is inadequate to describe nature.  If a population is
>separated from the "parent group", it may be subjected to slightly-to-very
>different environmental factors.  There's no reason for this to affect the
>parent population, so there's no reason to the parent population to change.

At some point you have to come to grips with the basic question of
what you want your classification to represent. If you wish it to
represent a contemporary time-slice through biological diversity, in
which all recognizable types are given equal status and general
categories are then put together on top of that in an ahistorical
sense,,,well then you have a system which follows the logic I think
you are presenting. Because what you are basically doing is
identifying the ancestral population (of BOTH contemporary
populations) with one of the contemporary populations, on the basis
of their similarity, irrespective of their history. But once you
start meddling with ancestors, you need a system which can deal with
history. You are ignoring
the fact (yes,,,real natural fact) that the ancestral population was
reproductivly contiguous through time with BOTH current populations,
and that this
ancestral status is in fact its REAL historical relationship to both
of them.
This is the real realtionships between the populations through time
and space, and I cant imagine why you claim that this has "nothing to
do with nature", for these relationships are certainly "natural".
Your system is inadequate to describe it. The bottom line here is
that each system describes what it deems important to describe, and
before we decide on a system, we have to agree on what it is we want
to describe. I had thought that there was wide agreement that it was
the historical branching pattern that we wished to describe, but I
guess the agreement is less widespread than I thought.
It seems to me that the cladistic system represents exactly what we
can conclude has happened historically: if we find a fossil from
before the separation, we can recognize a higher taxon which includes
the fossil and both contemporary populations. We can further
recognize the separated population as a unique taxon. And we
recognize the
remaining population as undiagnosable within the higher taxon. Dems
da facts, no?




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