Australopithecus and orangutans

[Richard Jensen]

One problem here may be failure to recognize how cladistic methods have
evolved.  In the "early" days of cladistics, a great deal of effort went
into hypothesizing, for each character, a character-state tree.  These trees
were often simple (in the case of two-state characters, 0 -> 1), slightly
more complex (e.g., 0 -> 1 -> 2 ), or worse (e.g., 1 <- 0 -> 2, etc.).  Each
character was represented by its own phylogenetic tree.  One prominent
cladist, when asked how the plesiomorphic state was determined, replied
"choose the next most closely related group."  As a consequence,
common=primitive (common in the ingroup, if the "next most closely related
group" was unknown; later expanded to include common in the "next most
closely related group), was an approach that was sometimes used to determine
the plesiomorphic character state for constructing character trees.

With advent of the outgroup approach, the practice of constructing
character-state trees a priori went by the wayside.  I don't know of anyone
working in cladistics today he begins by constructing character-state trees
independently for each character.

Dick

Julian Humphries wrote:

> John Grehan wrote:
>
> >
> > My understanding and practice in morphology is to designate apomorphic
> > characters.
>
> That is simply wrong.  The majority of workers (morphological or
> otherwise) do not a priori designate a character state (not character),
> as apomorphic.  How could you? Unless you know the truth ahead of time
> the characterization of a state as a synapomorphy of two taxa is a
> result of analysis, computer driven or otherwise.  Workers designate
> outgroups (and their states) as pleisiomorphic and let the chips fall
> where they may. Having the same state as the outgroup might be indicate
> a retained pleisiomorphy, or might be an apomophy at some level of the
> tree (see below).  There is absolutely no fundamental difference between
> molecules and morphology as to the assessment of "shared derived
> characters."
>
> In fact, the situation is made more complex due to optimization of
> character state evolution (equally parsimonious solutions, even on the
> same tree, may yield multiple distinct sets of shared derived
> characters, thus synapomorphies may depend on which optimization
> strategy you adopt.)  Thus, a state appearing in an outgroup and an
> ingroup may be a retained pleisiomorphy, or a novelty, depending on
> optimization. Characters with homoplasy, may, at some level, still
> diagnose major clades.  All of this complexity is why that "computer
> contrived analysis" (this is the kind of word baiting typical of
> Kinman), is so necessary.
>
> --
> Julian Humphries
> DigiMorph.Org
> Geological Sciences
> University of Texas at Austin
> Austin, TX 78712
> 512-471-3275

--
Richard J. Jensen              | tel: 574-284-4674
Department of Biology      | fax: 574-284-4716
Saint Mary's College         | e-mail: rjensen at saintmarys.edu
Notre Dame, IN 46556    | http://www.saintmarys.edu/~rjensen