cladism's greatest weakness

Barry M. OConnor bmoc at UMICH.EDU
Fri Sep 17 12:45:22 CDT 1999

At 8:22 AM -0700 9/17/1999, Ken Kinman wrote:
...  As for the problem of
>"birdness", it is very similar to the problem we had and still have with
>Unfortunately, strict cladists have used Hennig's assumption to mask the
>fact that they are just substituting one kind of arbitrariness for another...

That's a problem with "naming and ranking" which will always be arbitrary.
Monophyletic groups which are well supported by data are not arbitrary
within the context of that data set; paraphyletic groups, by their nature,
are always arbitrary; i.e. which groups are excluded from the monophyletic
group are up to the individual.  This is art, not science.  Thus all the
old "ad hominem" arguments that Hennig freed us from show up in this latest
round of "Wose/Mayr/Kinman" arguments.  Anyone can criticize art, but you
need more data or better methodologies to test hypotheses.

At 11:42 PM -0400 9/16/1999, John Grehan wrote:
... Thus
>the primitive Leiopelmid frogs may comprise a paraphyletic assemblage,
>but they still can show a real biogeographic pattern. The
>same goes for the primitive paraphyletic lineages in the ghost moth
>(Hepialidae) family that show a classic
>Australia-Southern Africa-Eurasia/North America track.

This is true only if you are totally up front about which lineages within
the monophyletic group you have excluded from your discussion; i.e. there's
really no such thing as a "paraphyletic lineage."  For example, one might
say, "the biogeographic pattern of monophyletic lineage A-idae (excluding
genera B, N, R, Q, Y, Z, and AA) shows a classic...track."  Would anyone
think this useful if all of those excluded lineages didn't themselves form
a smaller monophyletic group?  In your above examples of "primitive
paraphyletic lineages" which I take to mean "the monophyletic group
excluding one single derived clade," you may be suggesting that there is an
underlying ancestral pattern that might be masked if one included some
large derived lineage which showed an entirely different pattern.  But
including that derived group gives a better picture of the geographic
history of the entire lineage, even if it turns out to be more complicated
than one would like!
        - Barry

So many mites, so little time!
Barry M. OConnor                phone: (734) 763-4354
Museum of Zoology               FAX: (734) 763-4080
University of Michigan          e-mail: bmoc at
Ann Arbor, MI 48109-1079  USA

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