The attitrion of taxonomic expertise

Tom DiBenedetto tdib at UMICH.EDU
Sun Oct 20 10:02:33 CDT 1996


On Sat, 19 Oct 1996 21:12:29 -0700, Curtis Clark wrote:

>At 04:19 PM 10/19/96 +0000, Tom DiBenedetto wrote:

>I said homoplasious
>>characters are homologous at lower levels than originally proposed
>>(homoplasies are over-generaliztions). This refers to characters
>>which are then interpreted as convergences or reversals.
>
>Then you're wrong. (Or rather, you are redefining homoplasy, a word that has
>been used for 126 years with a meaning different than you give it.)

Sorry, but I have no idea what you are saying here. Lankaster
originally defined the term to mean similarity which is not present
by means of inheritance from a nearest common ancestor. That is what
the term has always meant in systematics. In a cladistic analysis we
make hypotheses as to the generality of homologous character-states
under the assumption of congruence. Instances of incongruence arise
from hypotheses which are overgeneralized relative to the predominate
pattern, and are interpreted as convergences or reversals. They have
always been referred to as homoplastic in systematics.  What
definition are you using?

 And it
>seems to me that a homology at a lower level than proposed is in fact a
>plesiomorphy.

???? I propose that wings in bats and wings in birds are homologous,
all had a single origin. I combine this hypothesis with all other
evidence and get a cladogram which indicates that bird wings may be
homologous within birds, and bat wings may be homologus within bats,
but the two conditions are independantly evolved. Thus they are
homologies at lower levels than originally proposed. This is
convergence, not plesiomorphy.
---------------------------------------------
Tom DiBenedetto
Fish Division
Museum of Zoology
University of Michigan




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