[Taxacom] Clade age

[Curtis Clark]

On 11/14/2011 12:35 PM, Richard Jensen wrote:

[I haven't read the Cladistics article, so I'll tread lightly.]

> I disagree with the idea that species names are merely diagnoses.

I'm not sure we're talking about the same thing. I don't see species 
*names* as diagnoses, what I'm saying is that useful characterization of 
a species consists of its similarities and differences relative to other 
species, which I think of as a diagnosis. ("Mere" diagnosis seems 
value-laden.)

> >  Species names are connotative, just as Linnaeus suggested.

Linnaeus's differentiae were effectively diagnoses, and as such were 
definitely connotative, since they consisted of a focused subset of 
information. I have always assumed that Linnaeus ultimately envisioned 
"definitions" in the Aristotelian sense (all the essential 
characteristics and none of the accidental characteristics), only 
because that would be theologically supported (I teach that Linnaeus was 
one of the last great truly scientific creationists, because he wanted 
to understand what constituted the originally created kinds). It is to 
this Aristotelian view of "definition" that I object.

>    And, as I
> >  argued in my paper in Cladistics, species names are not proper names,
> >  as the latter are commonly defined.  Species are natural constructs
> >  and can be defined by possession of certain properties, whether these
> >  be phenotypic traits or evolutionary origins.  Just as "triangle" is a
> >  shorthand expression for a two-dimensional construct defined by a
> >  given set of attributes,

To me, "triangle" is a bad example. It has a definition, "A polygon with 
three vertices." I suspect that in the realm of non-Euclidean 
geometries, there are cases where that definition is no longer useful; 
whether it has impeded understanding by mathematicians, I will leave to 
them.

> "Homo sapiens" is a shorthand expression for
> >  a natural entity defined by a given set of attributes.

I would counter that a species (as a natural entity) is "defined" by its 
membership, not by its attributes; the attributes are known only 
post-hoc. And adherence to definition can weigh an argument: Certain 
definitions of Homo sapiens would pretty much require that the 
stabilization and establishment of HeLa cells be regarded as a 
speciation event, since the entity no longer matches the definition.

Taxonomists' views of the species they study are subject to change. To 
me, that seems to require that definitions based on attributes must also 
change. And I suppose that one could look at that sort of taxonomy as a 
dialectic, with definitions-as-hypotheses being falsified, rejected, and 
new definitions formed. But I'm not sure that taxonomy actually works 
that way, and I don't think it's useful.

-- 
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Professor, Biological Sciences                   +1 909 979 6371