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John V Jackson wrote:
> --Orig. Message-- From: chris brochu <cbrochu@fmppr.fmnh.org>
> Date: Sun, 28 Mar 1999 12:06:57 -0600
> >John V Jackson wrote:
> >
> >>>[Matt T:] "It is hard to deny the power of the theropod hypothesis, ..."
> >
> >> People often cast the issue in the form of "theropod" vs "non-theropod",
> >> but there is more than one theropod theory, and most are mutually
> >> exclusive.  In some ways, all the wrong theories have more in common
> >>with each other than with the truth.
> >
> >But ARE these "mutually exclusive?"  There are quantitative ways of
> >addressing that question.  The days when we could simply step back and
> >say "Wow - those trees are, like, really different and stuff" are long
> over.
> The quantitative procedures for comparing them will depend entirely on the
> processes that created them. 

No - we're not comparing robustness, or the quality of the trees in any
way.  We're only addressing the question, "are these trees of a
fundamentally different shape."  It doesn't matter if we're comparing
trees generated cladistically, phenetically, from stratigraphy, from
maximum likelihood, or from a seance.

 The statistical algorithms used will have
> confidences associable with each feature of a tree or clad, but what if the
> trees were generated in some other way?

I think you're confusing measures of tree support with measures of
incongruence.  Measures of support will certainly depend on the method
of obtaining them, but if I'm only interested if two trees are
fundamentally different, it doesn't matter how we came to acquire them.


> >It is generally thought that highly congruent results from disparate
> >sources suggest an approximation of truth.  But, we don't necessarily
> >expect different data sets to yield precisely identical signals -
> Rough clusters around a target are to be expected, but though precision is
> not expected from every shot, the average of all the shots might be expected
> to have some significance if the weapon is "true enough".  No-one ever gets
> near my bullseye though!

But the weapons aren't always the same.  For most systematists, failure
to obtain the preferred result means one should reconsider the preferred