The attitrion of taxonomic expertise

Curtis Clark jcclark at CSUPOMONA.EDU
Sun Oct 20 18:34:15 CDT 1996


At 01:04 PM 10/20/96 +0000, Tom DiBenedetto wrote:
>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?

"When identical or nearly similar forces, or environments, act on one or
more parts of an organism which are exactly or nearly alike...[or] on parts
in two organisms, which parts are exactly or nearly alike and sometimes
homogenetic, the resulting correspondences called forth in the several parts
in the two organisms will be nearly or exactly alike....I propose to call
this kind of agreement _homoplasis_ or _homoplasy_....The right ventricle of
the bird's heart is not homogenous with the right ventricle of the mammal's
heart, nor the left with the left, but the two cavities in each case are
homoplastic." - Lankester, E. R.  1870. _Annals and Magazine of Natural
History_, series 4, 6:39-40.

>???? 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.

My mistake; I misconstrued "lower" as meaning toward the root of the tree of
life, rather than toward the tips of the branches (my botanical background,
no doubt). I hope you'll agree that a homology at a lower level in *this*
sense is a plesiomorphy.  Inasmuch as any feature coded for by genes that is
found in two siblings is a homology, of course you are right.

I'm done with this. I think I'll do some alpha taxonomy for a while....

------------------------------------------------------------------------
Curtis Clark                       http://www.is.csupomona.edu/~jcclark/
Biological Sciences Department                     Voice: (909) 869-4062
California State Polytechnic University, Pomona    FAX:   (909) 869-4396
Pomona CA 91768-4032  USA                          jcclark at csupomona.edu




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