Australopithecus and orangutans

[Michael Bayly]

P. Hovenkamp wrote:
>At 10:07 AM 5/15/03 -0500, Richard Jensen wrote:

>>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.

>Branham & Wenzel in a recent issue of Cladistics (19: 1-22) distinguish
>ordered from unordered characters in a morphological analysis of fireflies.
>The multistate ordered characters are in fact simple character state trees.
>The practice is alive and kicking.

Peter,
I think it is important to differentiate between "ordered" (as used by
Brenham and Wenzel) and "polarized" characters.  You can order your
characters, i.e., say that you logically can't get to state 3 from state 1
without going through state 2 (making the transition from 1 to 3, or vice
versa, cost 2 steps), without "polarising" them, i.e., constraining the
direction of change by, for instance, requiring that character evolution
actually went 1 to 2 to 3, not the other way round.  It is this step of
"polarising" that I think John Grehan has been talking about, and which
started this line discussion.

You are right in suggesting that the practice of ordering characters is
still alive and well (although in in my book you need a pretty good a priori
justification for doing so), but the practice of polarising characters a
priori is not so common, and character polarity is generally left to "come
out in the wash" by reference to the outgroup, and  congruence with other
characters.  Again, you would need pretty good reasons for choosing a priori
to polarise your characters.  If this were done wholesale, inferred
phylogenies would basically reflect the "answers" that you apparently knew
all along (since character coding will shoe-horn analyses into giving tree
topologies consistent with the state transitions you expect).


Mike



----------------
Dr Michael Bayly
Research Scientist in Plant Biosystematics
Museum of New Zealand Te Papa Tongarewa
PO Box 467
Wellington, New Zealand
Ph: +644 381 7262
Fax: +644 381 7070

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