parsimony/biology

[Pierre Deleporte]

At 21:07 26/02/01, Kirk Fitzhugh wrote:
>How does one test that hypothesis that a plan crashed as a result of engine
>failure? All historical explanations deal with testing in the same way. The
>past no longer exists, so what must be sought is evidence in the present of
>the events that occurred in the past. This is standard historical analysis,
>but for some reason has rarely been properly applied in this historical
>science we call phylogenetics.
>Quite fascinating.

Yes, perhaps fascinating that this doesn't seem obvious to everyone, but if
we read closely for instance the classic Farris 1983 ("The logical basis of
phylogenetic analysis"), we do find a frequently overlooked tentative
biological justification of standard cladistics (optimizing homology) taken
from biological evidence in the present:
(p. 19): "...it seems unlikely ... that homoplasy is universal.
Universality of homoplasy would imply in the extreme that organisms do not
generally resemble their parents, a proposition that seems at best contrary
to experience".
Isn't this a clear statement of a universally observed process in present
days populations (all organisms have parents and look very much like them),
which is extrapolated to the remote past as an "explanatory law" for
explaning the distribution of characters in taxa (phylogeny)?
As far as I know, stratigraphy is also performed by observing present
geological mechanisms of sedimentation and extrapolating to the past. And
Darwin observed artificial selection in pigeons before extrapolating
natural selection to the evolutionary past.
As historians, phylogeneticians can hardly proceed another way. The better
we will understand the present universal evolutionary processes, the better
we will reconstruct the history of evolution. In this respect, standard
cladistics aim at being a largely (but fortunately not completely) agnostic
approach, which we are often justified to use only for want of something
better, for want of more detailed knowledge of the evolutionary laws. We
implement an elementary set of evolutionary assumptions we trust.
Comparison with alternative methods is debatable on these biological grounds.

Pierre


Pierre Deleporte
CNRS UMR 6552 - Station Biologique de Paimpont
F-35380 Paimpont   FRANCE
Téléphone : 02 99 61 81 66
Télécopie : 02 99 61 81 88