Buddy Grah wrote:
> I must admit that I have only paid partial attention to this
> thread. Paul's statement caught my eye, however, since I guess I
> had also fallen into the trap of believing the two are different.
> The basis of my belief comes from my understanding of the term
> "species". I had understood it to refer to a group of
> individuals who could potentially interbreed and who were
> reproductively isolated from other groups. To the extent this
> notion is an accurate reflection of the "real world", it would
> seem to suggest that variation within a species and variation
> among species are two different things.
And Don McBurney wrote:
> Biologists do not treat species as sharp categories, but as generally
> non-interbreeding populations. There are many borderline cases. In
> other words, species are convenient categories, but we should not make
> the error of essentialism, as if they are platonic forms.
My understanding has always been much the same as what Buddy expresses. But
of course evolution does not heed "potential to interbreed". It heeds
_actual_ interbreeding of _individuals_, which is a far, far, far more
complicated thing. An essentialist notion of "species" that attended to
actual interbreeding would have to grant an almost infinite number of
different species (for example, a couple of billion species of human being).
I take this as a reductio ad absurdum for the notion of separate mechanisms
of evolution for within and between species.
A notion that relied on potential, rather than actual interbreeding would
only add a couple of layers of (unnecessary) complexity. Most significantly,
I challenge you to define "potential to interbreed" in such a way as to not
make a complete shambles of set of "species" we normally talk about. On top
of that, we'd be left with practically no knowledge of what animals belong
to what species - we actually have essentially zero knowledge of which of
our currently recognized species can successfully interbreed. Imagine trying
to set up the experiment - does a negative result mean these two species
cannot interbreed, or that these two _individuals_ cannot interbreed? (of
course, as alway, I don't take our inability to find something out to be
evidence that something doesn't exist. But it's still an interesting
thought).
But that's largely irrelevant - what matters is the fact that the notion of
species is one of categories defined for the convenience of human beings,
and mechanisms of evolution don't care at all what we think. Variation among
individuals occurs as a result of evolution, without paying any attention at
all to the genes carried by "potential mates". Only those carried by actual
mates make any difference.
(this is an interesting problem - in his "A Theory of Content", Jerry Fodor
has to cope with real-world effects of potential causes in his explanation
of how mental symbols can "mean" objects and events in the world. He thinks
he manages, but in my 1994 philosophy Masters thesis I knocked a rather
large hole in his theory, with significant help from Donald Davidson).
Paul Smith
Alverno College
Milwaukee
