Tom DiBenedetto tdib at UMICH.EDU
Wed Oct 2 09:13:51 CDT 1996

On Wed, 2 Oct 1996 07:44:02 -0700 (PDT), James Lyons-Weiler wrote:

> The "Hennigian algoritm" is model of evolution that excludes
>the following possible models:
[snip 6 examples]

>When one approaches their data with cladistics (or max pars, and other
>methods), one usally is not suspecting that any of these six alternative
>models of evolutionary process have been at work, messing up cladistic
>hierarchy in the distribution of character states among surviving and
>sampled data.

I disagree. The six examples you give do not address the question of
whether the algortihm represents a model of evolution. Obviously
there are certain basic assumptions in all systematic studies
(including such things as the very existence of historical
information); if you wish to consider these assumptions as comprising
a minimal model,,,well ok,,but you seriously confuse the issues in
terms of the debates between methods. Some methods use an explicit
model of how particular processes operate, and the phylogenies are
dependant on these models. Cladistic parsimony approaches do not use
a particular model of evolutionary processes, but rather incorporate
relevant knowledge at a prior stage, at the level of formulating
hypotheses of homology. The algorithm is left to function as an
objective pattern-extractor from a data-set of characters which have
already been accepted as homologous.

Tom DiBenedetto
Fish Division
Museum of Zoology
University of Michigan

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