[Fwd: Re: Probabilities on Phylogenetic Trees]

Tom DiBenedetto tdib at UMICH.EDU
Wed Sep 17 20:58:38 CDT 1997

 James Francis Lyons-Weiler wrote:

>        My point remains because the only type of hypotheses of
>        homology that are considered to begin with are those
>        that have already passed a series of tests to distinguish
>        homologies from non-homologies.

This is a PROBLEM?

>        Explicitly, the degree of
>        corrorboration afforded to the sets of congruent hypotheses
>        is lower than it could be because previously screened
>        hypotheses of homology have a a HIGH, not a LOW,
>        probability, as so the presence of congruence has a HIGH, not
>        a LOW logical probability, so boldness is low.

Here is a hint as to why your logic is faulty. In Poppers view (and
you are using his concepts so I imagine you are making reference to
him), a hypothesis of low boldness is indeed one with high
probability. It is also a hypothesis which departs minimally from
"adhocness". An ad hoc hypothesis is one which explains the details
of particular phenomena, with minimal recourse to general notions. It
is highly probable because it it says almost nothing beyond
describing the immediate phenomenon, and so it has low boldness. In a
parsimony analysis, the *least* parsimonious tree would be one which
maximizes ad hoc statements. Those 4000 instances of hair are not
one, they are 4000 separate instances. Describe each one
separately,,,no generalization, no boldness, very hgh probability.
Now think hard about what the opposite situation (*most* parsimonious
tree) would be,,,,,

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