Outgroups,etc

[Don.Colless at CSIRO.AU]

Dick Jensen wrote:
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The 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.
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I can't help asking here the question that I first asked many years ago
- and used to make my old friend Lars Brundin splutter into his vodka:
How do you choose a closely related group as an outgroup? That is, if
"related" here means "phylogenetically related" ( and I can see no other
valid meaning)- how was that relationship established. Lars used to
answer: "By advanced characters [I would have said "states"] held in
common". There is no prize for guessing my next question; but about
there we decided to give up argument and stick to  vodka.


Don Colless,
Div of Entomology, CSIRO,
GPO Box 1700,
Canberra. 2601.
Email: don.colless at csiro.au
Tuz li munz est miens envirun