necessary?

Nico M. Franz nmf2 at CORNELL.EDU
Thu Oct 2 23:11:50 CDT 2003


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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