Positivism in evolutionary science

Doug Yanega dyanega at MONO.ICB.UFMG.BR
Wed Dec 3 19:13:48 CST 1997

My two cents again...

James Francis Lyons-Weiler wrote:

>        In light of all these possible sources of noise, the central tenet
>        of phylogenetics should not be that evolution is, in general
>        or in detail, a parsimonious process.

Maybe I'm missing something, but I've never heard anyone state that they
thought evolution was parsimonious, or that this was why parsimony was used
in phylogenetic inference. The idea is that we want as objective and simple
an explanation as possible; if you condemn that, you're condemning the
essential underlying tenet of science itself. Parsimony methods minimize
the number of rejected hypotheses of homology in an analysis, with NO
reference to process assumptions whatsoever. Evolution does not need to be
parsimonious in order for parsimony methods to recover the overall pattern.
If you start adding process assumptions and incorporating *models* of
evolution, you've no longer got a simple hypothesis, but nested hypotheses
(one that your model is accurate, the other that the final result is the
simplest *within* the context of that model - ALL methods ultimately use
the *criterion* of the most parsimonious hypothesis).

> It is, as I indicated in
>        the second post in this particular thread, positivistic to presume
>        that parsimony will result in an accurate accounting of which
>        characters correctly indicate homology that indicates shared
>        relationships, rather than the alternative, namely, that
>        parsimony may be mislead by "something else".

Presuming that a tree is an ACCURATE hypothesis is not the same as
presuming it is the SIMPLEST hypothesis. Right?


Doug Yanega    Depto. de Biologia Geral, Instituto de Ciencias Biologicas,
Univ. Fed. de Minas Gerais, Cx.P. 486, 30.161-970 Belo Horizonte, MG   BRAZIL
phone: 031-449-2579, fax: 031-441-5481  (from U.S., prefix 011-55)
  "There are some enterprises in which a careful disorderliness
        is the true method" - Herman Melville, Moby Dick, Chap. 82

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