The attitrion of taxonomic expertise

Curtis Clark jcclark at CSUPOMONA.EDU
Fri Oct 18 19:51:01 CDT 1996


At 12:07 PM 10/18/96 -0700, James Lyons-Weiler wrote:
>  BTW,
>can't homoplasious character states be homologous?  So how can a
>hypothesis of synapomorphy test a hypothesis of homology?

Back when I learned cladistics, homoplasy was false homology (that is what
Ray Lankester meant, also, when he coined the term in 1870). Seems to me a
hypothesis of synapomorphy *is* a hypothesis of homology.

At 12:58 PM 10/18/96 -0700, Tom DiBenedetto wrote:
>>  BTW, can't homoplasious character states be homologous?
>
>Of course,,they ARE homologous, but at a lower level than orginally
>proposed. Matching character-states are generalized to the extent
>possible, and the congruence test reveals instances of
>over-generlization relative to the remaining data,,,,homoplasy.

Symplesiomorphy >< homoplasy.  In fact plesiomorphy IS homology, which is
what I hope is meant here.

>>So how can a
>>hypothesis of synapomorphy test a hypothesis of homology?
>
>The test is of the generality of the hypothesis; given that
>generality of homology is synonomous with the question of identifying
>the level at which the novelty arose, the test can be seen as a test
>of homology itself. On some level though, all heritable characters
>are homologous, even if only with the terminals.

All heritable characters *derived from common ancestry* are homologous.

Maybe I'm getting crotchety as I get older, but it seems to me that implicit
in a lot of the discussion that I see (not necessarily here) is the idea
that homology is simply a matter of support by the data.  In "old-time
cladistics", homology was a reality of evolution that we sought to discover.
And also a hypothesis that we sought to falsify. It's true that congruence
is consistent with homology, but it can never prove homology. Incongruence
can falsify homology, however.

Okay, I'm done; time to take my Metamucil.

------------------------------------------------------------------------
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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