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Re: More on classification.



Last week Stan Friesen  <swf@tdat.ElSegundoCA.NCR.COM> presented a dinosaur
classification and then an explanation of its rationale
..
>So, I presented my alternative classification.  It is
>more efficient as a filing system, since it has fewer levels,
>and on average 3-5 subgroups for each taxon, instead of the
>2-3 of the cladistic classification.  (Cognitively, 3-5
>subgroups is more 'natural' for the human mind than two).
..

        If the only reason that we classified taxa was to have good ways to
remember them then we could use all kinds of criteria, (group all the big
ones together...).  But I felt  moved to write because the tone of Stan's
note made it sound as if the issue between cladistic/phylogenetic
classification and his was one of convenience.

>[a cladistic classification] results in unbalanced classifications,
>with a few large, morphologically heterogenous groups, and many small,
>slightly differentiated groups.

        But the important insight that is being missed here is that since
the middle of the last century we have realized that all organisms are part
of one tree of life, and except for examples of information being moved
from one taxon to another (via virus carrying DNA, or maybe parasitic mites
carrying DNA between Drosophila spp.) this tree is a series of bifurcations
(certainly the case in dinosaurs).  Cladistic classifications (properly)
emphasize this realization... if we were landscape architects we would find
other classifications useful (shade plants, dry adapted plants,...) but
with dinosaurs we are almost certainly trying to understand the
relationships between groups.

        There is a further issue of whether we should use new names when a
particular linneage has changed a lot (e.g. birds).  I don't want to recap
all of the arguments about these topics here*.  But I do want to reassert
the importance of categorizations that capture more than "cognitive
convenience."

        Jeremy

*for discussions of the issues involved see;

de Queiroz, K and J. Gauthier: 1990, 'Phylogeny as a Central Principle in
Taxonomy: Phylogenetic Definitions of Taxon Names', _Systematic Zoology_
39, 307-322.

de Queiroz, K.: 1992, 'Phylogenetic Definitions and Taxonomic Philosophy',
_Biology and Philosophy_ 7, 295-314.

Sober, E.: 1988, _Reconstructing the Past.  Parsimony, Evolution, and
Inference_,MIT Press, Campbridge.

Ridley, M.:_Evolution and Classification.  The Reformation of Cladism_,
Longman, London.

Gauthier, J.:1986, 'Saurischian Monophyly and the Origin of Birds', in K.
Padian (ed.), _The Origin of Birds and the Evolution of Flight_, California
Academy of Sciences, San Francisco, pp 1-55.

        :::::::::::::::::::::::::::::::::::::::::::
        Jeremy Creighton Ahouse (ahouse@hydra.rose.brandeis.edu)
        Biology Dept.
        Brandeis University
        Waltham, MA 02254-9110
        (617) 736-4954