Ranks (was: Fwd: Nomenclature and classification)

[Barry Roth]

--- Philip Cantino <cantino at OHIOU.EDU> wrote:
> Gurcharan Singh wrote:
>
>
> >   I think a distinction has to be made between
> whether we are dealing
> >with
> >biological entities (species and infraspecific
> taxa) or artifacts
> >(supraspecific taxa). We won't discover a
> supraspecific taxon (but
> >rather
> >create one to ease our process of classification).
> If we discover a
> >biological
> >entity (It would a matter of taxonomic judgement
> whether to consider it
> >a
> >species, subspecies, variety or even a form if you
> like it), its
> >position in
> >different classification systems would remain
> unaltered,  except when
> >you make
> >a drastic change of shifting it to a different
> genus. The names of
> >different
> >supraspecif taxa are, however, clearly linked with
> the classification
> >scheme
> >you are following.
>
>
> This distinction between species and supraspecific
> taxa does not
> apply to phylogenetic nomenclature.  Clades (the
> only supraspecific
> taxa in phylogenetic nomenclature) are not human
> constructs.  A clade
> is a biological entity--a complete product of
> evolution that exists
> whether or not we discover it and whose existence is
> hypothesized
> based on evidence.  One of the things that I find
> philosophically
> appealing about phylogenetic nomenclature is that
> the entities being
> named have an objective reality (though they are not
> necessarily
> easy to discover), whereas I would agree with Dr.
> Singh that many
> supraspecific taxa that have traditionally been
> recognized in
> Linnaean classification are human constructs.

Moreover, what is ineluctably a human construct is the
system of ranks or categories by which canonical
systematics chops up the hierarchy of taxa.  There is
not a universally agreed-on feature that makes a taxon
have the rank of "class" or "family."  (Hennig wanted
the ranks tied to age, but that seems not to have
worked out.)  I am reminded of Parky Sharkey's
definition of the family:

"A family is a group including one or more genera (and
itself included within a higher-ranked taxon) of a
size and inclusiveness determined by common usage and
mutual (although not necessarily explicit) agreement
among taxonomists more or less familiar with the
organisms involved."  Sharkey, P.  Unpubl.
Deconstructing Systematics.

Anyone have a better definition?

Barry Roth
(who has been wanting to use "ineluctably" in a
sentence for about a week now)

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