Cladistics and "Eclecticism"
SDMANNING at ASUB.EDU
Tue Feb 5 16:30:43 CST 2002
At 09:50 AM 1/30/02 -0600, Tom Wendt wrote:
>Tom DiBenedetto says:
>"8- "Important" nodes, or what Denis refers to as "significant gaps", are no
>different from anyother node. Their "importance" means nothing more than
>that scientists find them to be interesting to discuss, for whatever reason."
>There are several separate threads within the recent discussion, and one of
>them keeps coming down to the same thing; cladists are interested only in
>branching patterns, which they equate with "the history of life." The
>amount and type of evolutionary change that occurs (or doesn't occur) along
>the way is apparently of no interest, or at least not worthy of inclusion
>in a classification. Eclecticists, as Ken calls them, feel that amount
>and type of change should be included in the classification (in addition to
>branching patterns), as difficult as that may be to do in practice. I
>don't think that the discussion is getting any closer to bridging that gap.
>Cladists criticize eclecticism for the the lack of "repeatability" etc.,
>but that is a methodological criticism and misses the deeper point: do you
>want your classification based on branching patterns only, or on branching
>patterns plus amount and direction of evolution? Just because a strictly
>cladistic classification is seemingly easier to erect [at present] in a
>supposedly rigorous fashion is no argument, by itself, for its being the
>optimal classification to which we should aspire.
Is this not really an argument for extensive research on which genes
control which traits in any species? When and if we obtain an idea of the
"amount and direction" of morphological change caused by each mutation we
will be able to better evaluate whether morphological divergences, even
major ones, represent single or cumulative events. Until then,
morphological data seem doomed to remain less reliable than others.
However, even if we reach the point of knowledge alluded to in the last
paragraph, we will further have to consider the probable adaptive
significance of the trait controlled by the gene - is it probably strongly
selected for or against in its probable climate? For paleontological work,
this seems crucial (to this non-paleontologist) to interpretation of the
probable "amount and direction" of evolution represented by morphological
and anatomical differences. For work on extant species, I argue for
studying the amount of plasticity for the character; climate; probable
adaptive significance of the character state; and geographical location of
the specimen under investigation vis-a-vis other specimens of the same
species, if any non-DNA data are to be included in the analysis of amount
and direction of evolution (as I still think they should be).
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