Real taxa

[Richard Jensen]

Pierre,

Perhaps you have taken Stephan Helfer to literally.  I don't think he
intended to imply that these organisms are making conscious decisions, and
his use of essence is not to be taken as an "essentialist" view of taxonomy.

I believe that Stephan has made a very good point:  a practicing taxonomist
recognizes a particular group as a species (based on a variety of criteria)
called X;  later, another taxonomist independently realizes that there is a
type of parasitic organism that occurs on, and only on, individuals that are
classified as species X.  I would argue that species X constitutes an
objectively recognizable natural entity; its recognition as a group is no
longer dependent on the vagaries of human perception - the parasite's
host-specificity is an independent source of evidence.

Of course, it was human perception that yielded the correspondence between
host and parasite.  But, any attempt to intrepret nature is dependent on
human perception.  The question becomes, are our human perceptions consistent
with those made by other organisms?  For most organisms, these "perceptions"
are programmed reactions.  Does a bee really have any choice about which
flowers it visits?  Probably not.  Bees are programmed to visit flowers that
provide certain sensory stimuli.  We can then observe this interacton and
conclude that there are two entities that have evolved in response to each
other and this co-evolutionary interaction is completely independent of human
perception (i.e., whether we recognize it or not, the interaction
continues).

So, species X is a real entity, not because humans say so, but because human
perception of the existence of X is corroborated by host-specifity of the
parasite.

OK, fire away!

Dick

pierre deleporte wrote:

> A 15:26 30/09/2004 +0100, Stephan Helfer wrote:
> >  Providing we
> >accept, for the purpose of this argument, that there are real units out
> >there
>
> You mean "real classes" out there ? "Real concepts" out there, and not in
> the brain of a thinking being ?
>
> >  and that things which are measurably alike are in essence
>
> You mean "essence" ? Which kind ?
>
> >  alike
> >(i.e. two snow flakes are essentially the same,
>
> "Essentially" ? In which respect, and for which observer ?
>
> >Other organisms share this perception of likeness: Many pollinators
> >appear to have concepts of "kind";
>
> Bumblebees have concepts ? You mean that ?
>
> >  similarly, parasitic and mutualistic
> >fungi, animals and plants have concepts of "kind"
>
> Fungi too, by the way...
>
> >In consequence, if we accept the reality of these organisms, our own
> >concept of taxa can be either challenged or supported. Many rust fungi,
> >for instance, only infect a single "species" (as humans understand it)
> >of plants; thus confirming our concept of similarity.
>
> I don't ask fungi to validate my concepts of similarity, sorry...
>
> >   in making taxonomic decisions in order to gain a livelihood...
>
> And fungi make decisions. Likely not of the same kind as ours I guess...
>
> Decidedly, I don't buy the "essence" of your argument at all.  ;-)
>
> Best,
> Pierre
>
> Pierre Deleporte
> CNRS UMR 6552 - Station Biologique de Paimpont
> F-35380 Paimpont   FRANCE
> Téléphone : 02 99 61 81 66
> Télécopie : 02 99 61 81 88

--
Richard J. Jensen              | tel: 574-284-4674
Department of Biology      | fax: 574-284-4716
Saint Mary's College         | e-mail: rjensen at saintmarys.edu
Notre Dame, IN 46556    | http://www.saintmarys.edu/~rjensen