Paraphyly=mistakes? (There's the rub)

Thomas DiBenedetto tdib at OCEANCONSERVANCY.ORG
Tue Jan 8 17:28:20 CST 2002

-----Original Message-----
From: Dr. James Adams
          Okay, so paraphyletic groups do not include all of the original
ancestors' descendents, and may not represent what some people would call
"natural" or "real" groups.  I say, so what?  It doesn't mean that a
paraphyletic group is not a useful way of communication.

I recognize that paraphyletic groups may have some use in the general
culture (as may polyphyletic groups) - I have no objection to a field guide
of "reptiles" and amphibians. Heurisitic classifications have their place.
The issue we are addressing though is the scientific classification - the
system to be taught to, and used by scientists in their work. I think it is
essential that the scientific classification be rigorously aligned with our
best inference as to the true historical branching pattern. Since we have
all (I should hope) accepted the evolutionary paradigm, we should recognize
that artificial groupings are not only meaningless, but downright deceptive
if used (as they have been) to make biological process arguments. If you
wish to analyze the dynamics of evolutionary change, of what possible use
would it be to consider Reptilia in its paraphyletic sense? The evolution of
birds has been the most interesting thing that ever happened in reptilian
evolution - what sense could one make of this if birds are artificially
placed in a separate category? Ken has raised the standard point that
Darwinian systematists want to incorporate an anagenetic divergence factor
in their classification schemes - this may make sense if you are trying to
produce a synopsis of evolution for the general public, but it is a terrible
idea if you wish your classification to be a useful tool for increasing
scientific understanding of taxa and their evolution. It seems clear to me
that the only useful approach is to have a classification that recognizes
real historical units, and to then map divergences on that tree. You can
then calculate precise values for the divergence in various lineages and
compare and contrast or summarize them, rather than having only extremely
crude statements such as that birds have somehow evolved enough to be
considered on an equal level with the rest of the reptiles. That is an
utterly useless scientific statement, and yet it is the best that can come
of the Darwinian strategy. This system has been abandoned by scientists for
this very reason - it may make for interesting cocktail chatter to know that
Kinman thinks that taxon X deserves to be ranked as a class whereas
DiBenedetto thinks it should only be an order - but basically who cares? And
what good is it? However, to have a clear picture of what the real
historical lineages are is profoundly important to advancing scientific
understanding of all taxa.
I really can't believe that we are still having this conversation in the
twentyfirst century.

Tom DiBenedetto

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