2000 years of stasis

B. J. Tindall bti at DSMZ.DE
Mon Feb 7 09:57:20 CST 2000

Thomas Lammers wrote:

>Perhaps.  But the fact remains that molecular data for use in systematics
>are 99.9% analyzed in some cladistic fashion.  Molecular data are ideally
>suited for cladistic analysis (as compared to, say, quantitative morph
>features) due to the large number of characters, and the paucity and
>distinctness of the states.  For better or worse, molecular biology could
>not have made the inroads and the contributions (a double-edged sword if
>ever there was one) that it has made to biologivcal systematics  without
>cladistics.  Cladists may not have planned to have molecular biology crawl
>in bed with them, but it did.
Can't agree with this statement 100%. Perhaps in zoology this is true, but
this is not true in microbiology. Neighbour-joining and De Soete's least
squares system (to name just two) are essentially phenetic. As far as I can
see all this calibration of sequence diveregence against geological time is
also based on degrees of difference, which has one foot (if not both) in
phenetic (i.e. overall similarity) evaluation. Right at the very begining
of 16S rRNA cataloguing there was a discussion about the Sab values being
phenetic which resulted in a very hot debate because certain fractions
wanted them to reflect evolution and were therefore "phylogenetic" (but not
sensu Henning and certainly not cladistic). In fact certain groups in
microbiology now generate consensus trees based on the results of three
kinds of analysis - Neighbour-joining, parsimony, and maximum likelihood.
Brian Tindall

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