Positivism in evolutionary science

James Francis Lyons-Weiler weiler at ERS.UNR.EDU
Thu Dec 4 10:21:01 CST 1997

On Thu, 4 Dec 1997, Tom DiBenedetto wrote:

> discrepancies. Popper goes on at length about the desirability to
> depart from ad hocness; it is directly related to the
> "outlandishness" of the hypothesis (actually it might be better to
> simply refer to the information content of the hypothesis).

        No; as I read Popper, an ad-hoc hypothesis is one that is
        tacked on to save a failed theory, and that is, in principle,
. To
> this back to phylogenetics, the most parsimonious tree is the
> hypothesis which has the greatest information content; it can account
> for the data more efficiently than any other hypothesis. A hypothesis
> of independant origin for every taxon (creationism) can account for
> the same amount of data, but it requires a separate (ad hoc)
> hypothesis for each novelty, and is least parsimonious.

        The limitation here is, as we've discussed at length before,
        the utility of parsimony as the test.  Other criteria can be
        used as more sensitive, more exact, and more demanding
        (more critical) tests than provided by parsimony.

        I am familiar with Farris' arguments on minimizing ad-hocness.
        However, that justification is intrinsic to the parsimony
        paradigm.  There is far more to phylogenetic systematics
        than parsimony.  Second, simply because one has postulated
        the simplest hypothesis(and knows it) doesn't mean that the
        hypothesis is afforded any greater corroboration than, say,
        the most complex hypothesis.  That's because corroboration
        is a function of boldness.  If, for a set of organisms,
        it could be shown experimentally that the longest tree was
        in fact the true tree, we would all be very much surprised;
        as a result, the longest tree (in this case) would be
        afforded a greater amount of corroboration than any other.
        We would not be surprised if the shortest tree was true,
        and thus parsimony is not an sufficient test.
> >     What Popper saw as the only link between the degree of
> >     simplicity of a hypothesis and corroboration is often
> >     confused, too.  He did not say that simpler hypotheses were,
> >     automatically, better corroborated.  He said that they
> >     were, in general, easier to test (i.e., better corroborable),
> >     and that therefore we should examine the simple hypotheses
> >     first.
> No, you are missing something here. Simpler hypotheses are better
> corroborated because they inherintly say more; they have higher
> information content; they are inherently more bold.

        No, no, no.  That's the caricature of Popper than has
        grown up inside phylogenetics, and it is ALL backwards.

>. A
> hypothesis which postualtes a single transformation, and thus implies
> a grouping (of say, 8 taxa), is saying more than a hypothesis which
> postulates three transformations and thus implies several smaller
> groups, or a hypothesis which postulates many transformations and
> implies nothing about relationships.

        One transformation says more than three?  Information content
        a la Popper is the new information that a hypothesis provides
        about nature IF is has passed a test, beyond that which
        we already expect given the background knowledge.  Popper's
        formalized relationships among h (hypothesis), e(evidence, or
        test statement), b (background knowlegde), I (information
        content), C (corroboration) , and empirical content
        (testability) form a consistent calculus that has
        repeatedly been corrupted in its application to
        phylogenetics.  The best and most accurate representation
        of Popper in our literature has been that of Faith, Trueman
        and Cranston - the early papers (90-91).  IMHO, your
        understanding of falsficationism has been tainted by
        misunderstanding and misapplications by others.

        David Miller has a wonderful compilation of Popper's writings
        (Princeton Univ. press, 1985) in paperback (ISBN 0-691-02031-0)
        which provides a great many instances wherein Popper explains
        the formal calculus of corroboration.  It's a worthwhile read.

        James Lyons-Weiler

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