Clades, cladons, and "cladifications"

Mon Jun 14 10:06:35 CDT 2004

In a message dated 6/14/2004 12:10:25 AM Pacific Standard Time,
nmf2 at CORNELL.EDU writes:

> >David Hull in his 1979 paper ("Limits of Cladism"; Syst. Zool.,
> 28:416-440) >pointed out the following dilemma: "no methods have been set
> out thus far >which permit the inclusion of both sorts of information
> [genealogy and >divergence] in a single classification in such a way that
> both are >retrievable."
> ---This doesn't seem right. One can (and often does) map derived character
> states along branches. These can convey precisely the kind of information
> about "amounts of divergence" or "evolutionary distinctiveness" that, as
> some have claimed, can't be expressed cladistically. One would hope that
> if there really was a deep problem with expressing amounts of
> transformation in cladistics (not just branching patterns), the method
> wouldn't have caught on so broadly by students of evolution.

Yes, the number of derived characters can be plotted on the branch showing
the amount of divergence, but what Hull was trying to say is it cannot be
expressed in a classification based on tree topology. The classification is either
based on the tree topology or the degree of divergence not both at the same
time. Ken disagrees, of course.


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