More on the 'cladistics' of sequences

[John Grehan]

At 12:42 PM 6/6/04 -0500, rjensen at saintmarys.edu wrote:


>OK, then please explain to me how, in the absence knowledge of
>phylogenetic relationships, you determine which states are derived before
>conducting the analysis.

I did not say character states are determined in the absence of knowledge
of phylogenetic relationships! To the contrary, I am always referring to
evaluation of each character with respect to an outgroup before the analsis.

> > If the decisions for what constitutes the ancestral states are
> > verifiable then they are not arbitrary in the sense that the
> > choices are not defensible.
>
>Verfiable by what criteria?  And, whose definition of verifiable?

One can document each character for the outgroup and ingroup. By this
documentation it is possible for each character to be independently
verified or refuted by another individual (trouble with hominoid
systematics is that many of the characters are so poorly described if at
all that event his process becomes impossible for some characters).


>I did not suggest that the systematist knew the group poorly.

No, but if one cannot polarize the characters and determine which are
potential synapomorphies before the analysis then the implication is that
such individuals do not know their group very well.

>It is essential that the systematist start with well-founded knowledge of
>group characters.  Obviously, once the analysis is conducted, it is
>necessary for the systematist to critically evaluate the result with
>respect to which characters provide support for the relationships.

I would start with some critical evaluation before the analysis to restrict
the data set to potential synapomorphies. Then the evaluation after the
analysis can take place with respect to one's initial determination.

John Grehan



>Dick