Darwin (was: Phylogenetic evidence)
skala at INCOMA.CZ
Fri Jul 26 09:12:35 CDT 2002
From: pierre deleporte [mailto:pierre.deleporte at UNIV-RENNES1.FR]
>But they [clades] must share characters in common, unless they would not be
>identified as clades.
Well, only to complete the argument:
character matrix (+ = apomorphy)
1 2 3 4 5
A - + + + +
B + + + + +
C + + + - -
D + - - - -
=> cladogram (parsimonious now, I hope!)
...where no character state is shared by all its members.
...but more interestingly: Pierre:
>Clades are classes if you consider reversals as apomorphies, what cladists
>do as a rule. They classify organisms AFTER phylogenetic analysis, thus
>'reversed' absence of characters, as well as "reversed" states similar to
>plesiomorphic ones, are identified as apomorphies ...
>Classes based on these nested sets of synapomorphies, interpreted in the
>light of the cladogram, including possible apomorphic absence - reversals,
>are thus classes of equivalence, not similarity clusters.
>In my view, you can't reason for phylogenetic systematics by considering
>"face value" character states in the data matrix.
Pierre, do you mean that the "reversed" character state is re-interpreted as a completely new character state (different from the plesiomorphy)? In that case you also cannot have homoplasies but only a series of independent (though indistinguishable) apomorphies. Consequently, all the indexes of homoplasy are useless - you will have always fully resolved cladogram. Is this what you want to say?
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