Positivism in evolutionary science

Tom DiBenedetto tdib at UMICH.EDU
Wed Dec 3 11:25:54 CST 1997

 James Francis Lyons-Weiler wrote:

>        It is
>       a positivistic position to state that most of the
>       traits that organisms aquire through genealogy will
>       have remained informative about shared ancestry.

Who makes such claims? Advocates of parsimony merely claim that real,
observed patterns do exist (I think you agree with that), and that
descent is a suitable explanation for organism-wide consistent
patterns in the distribution of heritable characters amongst taxa.
Whether that pattern is formed by "most of the traits" aquired
through descent does not seem to really be an issue, as far as I see.

>       it's a matter of signal:noise, and to focus only on what we
>       perceive as signal without (adequately) measuring the
>       noise is positivistic.

It seems to me that parsimony methods are quite efficient at
distinguishing the hierarchical signal from the incongruent noise.

>         Relying on (parsimony) trees
>       to tell us about the reliability of the information
>       in the distribution of character states among organisms
>       is like trying to receive instructions on how to construct
>       an antenna through the antenna you're trying to construct.

The parsimony tree merely reveals the hierarchical order in the
dataset. The question of the reliability of that data is another
matter. If you claim that real patterns can arise coinidentally; i.e.
that a real pattern might be in fact a result of more than one causal
factor working to produce an artifical pattern, then I guess I would
like to know what such factors are, and how that all works.

>       Some parts of the information may come through, but other
>       parts are jumbled.  It's even worse than this analogy, because
>       at least with radio or television signals we can immediately
>       recognize the noise (scatter).  It would be as if the antenna
>       would organise the noise into coherent sentences about the
>       contruction of the antenna that were misleading - and we
>       would have no independent means of checking the quality of
>       the reception, because the antenna is making "sense" out
>       of "nonsense".

This seems to imply that distributions can be patterned,
organism-wide, by a multiplicity of factors all working to produce a
single coherent pattern. How can that be?

Tom DiBenedetto                 http://www-personal.umich.edu/~tdib/
Fish Division                                   tdib at umich.edu
University of Michigan Museum of Zoology

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