necessary?

Jan De Laet jdelaet at NATUURWETENSCHAPPEN.BE
Fri Oct 3 10:12:59 CDT 2003


Nico, you can rest your case, as far as I am concerned (well, apart
from your botanical example, as Paul van Rijckevorsel pointed out).
I would just like to rest it a bit more: the theory of cladism
(parsimony analysis) does NOT require adherence to essentialism. As
you correctly note, "unique synapomorphy and perfect congruence are
not "necessary"". This is true in practice as well as in theory
(and one does not need to be a Sherlock to figure that out :-)).

I think it is also worth pointing out explicitly that your note
shows that parsimony analysis has nothing to do with monothetic
classification. Being monophyletic and being monothetic are
simply two different things, and the theory of parsimony analysis
does NOT rely on the the methodological assumption that 'monophyly =
monothetic', as Richard Zander seemed to imply the other day.

Of course, if one happens to find unique synapomorphies for clades,
that's nice, not in the least for practical reasons. But parsimony
analysis does not assume that such things exist, not in theory and
not in practice. And even if, in a particular analysis, unique
synapomorphies are found, they don't have to be interpreted in an
essentialistic way. Why insist on that interpretation? Looks like
a strawman to me, or some severe misunderstanding of current theory.


Jan De Laet
Freshwater Biology
Royal Belgian Institute of Natural Sciences
Vautierstraat 29
Brussel
Belgium

"Nico M. Franz" <nmf2 at CORNELL.EDU> wrote:

> If tomorrow an orchid species would lose its triploid endosperm or an ant
> evolved another pair of legs, we would still be able to refer to these new
> taxa as angiosperms and insects, by virtue of the remaining associated
> (congruently nested) properties they possess. In practice this happens all
> the time. We call snakes tetrapods in reference to their shared
> evolutionary history and attributes (perhaps even the underlying genetic
> basis for legs which they should still have) - although they are "legless"
> phenotypically.
>
> Again I'd commend the article by Boyd. Higher taxa can be individuated in
> reference to homeostatically maintained sets of properties. Often these
> properties have a causally sustained yet imperfect association in space
and
> time. The secondary loss of one among many of them is not necessarily an
> obstacle to reference. In this sense evolutionary naming may differ a bit
> from the way in which we name gold.
>
> In practice unique synapomorphy and perfect congruence are not
"necessary",
> as I think the snake example shows. Homoplasious characters play an
> enormous role in cladistic reference. If the theory of cladistics requires
> the adherence to essentialism, then it seems at least that actual practice
> hasn't paid much attention to that theory (can I now rest my case?)
>
> Regards,
>
> Nico Franz
>
> At 12:09 PM 10/3/2003 +1000, you wrote:
> >The notion that classical taxonomy is essentialistic, is of course (as
> >pointed out by Nico Franz) nonsense. Its polythetic nature was examined
> >back in the 60's, by inter alia, David Hull (in what I seem to remember
> >was his PhD thesis!). The amusing fact is that cladism is absolutely
> >essentialistic. Its taxon names are rigidly defined by a set of necessary
> >and sufficient conditions: the posession of what are BELIEVED to be
unique
> >apomorphies (by, of course, a set of self-appointed Sherlock Holmes').
> >
> >Div of Entomology, CSIRO,
> >GPO Box 1700,
> >Canberra. 2601.
> >Email: don.colless at csiro.au
> >Tuz li munz est miens envirun
>




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