FW: Platnick's recent lecture (URL link)

[Curtis Clark]

At 01:14 PM 3/7/2002, Bill Shear wrote:
>Norm states that the retention of the ability to interbreed is a
>plesiomorphy and so could not be used to define a species.  However, the
>ability to interbreed is not the criterion used in the BSC to define a
>species--it is the reproductive isolation of that population from other such
>populations, and that, surely, is an acquired apomorphy.

1. Proponents of the BSC often assume that lack of reproductive isolation
indicates "same species", and yet the important factor is gene flow. Just
because members of two species can produce fertile hybrids, that doesn't
mean there is significant gene flow between the species.

2. More important: Prezygotic isolation mechanisms, especially those that
operate in sympatry, are indeed most often autapomorphies of the lineages
that possess them. It is difficult to postulate selective explanations for
postzygotic mechanisms, however--they tend more toward the stochastic.

At 01:21 PM 3/7/2002, Thomas Lammers wrote:
>I prefer to think of the ability to interbreed as an indicator of the
>degree of HOMOLOGY of the respective genomes.  Surely that concept of
>homology can be made to fit a cladistic viewpoint somehow ...

In the case of postzygotic barriers, this is indeed an exceedingly crude
measure of genomic homology, in perhaps the same sense that Lankester used
the term. But there are a number of examples of *unilateral* prezygotic
barriers, which would suggest that species A is more "homologous" to
species B than species B is to species A.


--
Curtis Clark                 http://www.csupomona.edu/~jcclark/
Biological Sciences Department             Voice (909) 869-4062
California State Polytechnic University      FAX (909) 869-4078
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