Positivism in evolutionary science
ricksonf at AVA.BCC.ORST.EDU
Thu Dec 4 09:40:15 CST 1997
The comment about dropping a data set and doing another phylogeny suggests
a problem I have noticed over the past few years, i.e. many people
(students?) are busy doing phylogeny studies without really seeing much, or
any, of the organisms in the field or using only a cursory examination of
data other than the single "method of choice," data set. I produce a
suggested phylogeny, from which to work, after seeing the plants (and their
ants in my case) in the field, looking at herbarium material for variation,
and doing some cell by cell anatomy for still another level of comparison.
Yet I now see cladograms made from "100" pieces of leaf material sent from
outside sources. Certainly any information on possible relationships is
important and welcomed, but I suspect the "guess level" only decreases as
the biological information increases.
I am not a taxonomist in any sense, but I do rely on suggested evolutionary
relationships for guidance in how morphology relates in different taxons.
Therefore, ideas based on a single data set, or data type, seem suspect at
best.....even though I do recognize that proper nucleic acid information
might be the most informative of all.
As one last offering, I see the arguments about how perfect a cladogram
might be (this thread) somewhat akin to angels on the head of a pin. If
one runs all of the corroborative statistical tests available, after using
multiple levels of information, and then makes a choice, that is the best
one can do. Maybe, at some time in the future, better tests will be
developed....but for now one has to go with the best possible shot.
Science changes with time no matter how perfect we think we are at present,
and you should be able to change with it as new ideas demand. Science (and
your cladogram) is a work in progress, not religion.
Professor of Botany
Department of Botany
Oregon State University
Corvallis, OREGON USA
Tele: (541) 737-5272
Fax: (541) 737-3573
e-mail ricksonf at bcc.orst.edu
> As an example, take your favorite dataset and use it to generate a
> using your favorite parsimony-program. All fine.
> Now, drop the dataset on the floor (metaphorically speaking), reassemble
> a hurry and again produce a cladogram. Does your favorite program say:
> this data was not reassembled correctly? No, it just churns out another
> cladogram, and the only indication that you'll see that your data were
> not in their original state is a lowered consistency index.
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