Real species and ideology

Richard Pyle deepreef at BISHOPMUSEUM.ORG
Tue Apr 20 22:39:49 CDT 2004

Not sure if Taxacom will le me send another post, but here goes:

Ron Gatrelle wrote:

> Refugia and
> biogeographical isolation and suture zones reveal that many so
> called clines
> = blend zones are actually tension zones where two once separated
> subspecies
> are now in contact - usually for the first time in their several thousand
> year separate evolution from long gone ancestors.   Thus, I look at the
> reproductively "stable" regional populations (subspecies or species) and
> discard the in-betweens (populations or hybrids) OR see them as
> buffer zones
> maintaining the phenotypes (subspecies) or genetic integrity (species) of
> the taxonomically delineatable segregates.

But on what time scale do you define the word "stable"?  We've only been
paying attention for a few hundred years -- probably not long enough to
identify "stable" on an evolutionary time scale.

> If I were looking at the Missouri River and then the Mississippi River I
> would see two rivers.  Then I could go to where the Missouri
> flows into the
> Mississippi and at the junction (blend zone) try to figure out where one
> stops and the other begins - and then expand that intellectual exercise
> until I have denied the existence of both the Missouri and Mississippi.

Maybe you would deny the existence of both rivers, but I wouldn't.
Actually, what I would recognize as "reality" are individual water
molecules.  If I happened to stumble onto the rivers at a point well
up-stream of the junction (where the exchange of water molecules between the
two conduits is trivial -- limited to evaporation/precipitation, or
migration via groundwater), then I would cluster the two sets of water
molecules into two separate defined rivers.  If I happened to encounter the
river downstream of the junction, I would be confident in assigning the
entire set of water molecules from shore to shore into a single
species...err...river.  But if I happened to hit the point of confluence,
I'd be unsure whether ay particular molecule came from one source or the
other, so I would call"subrivers".

The river analogy is messy because it's flowing in the opposite direction
(towards convergence, rather than divergence).  A better analogy would be a
river that forks.  When examining the two paths downstream of the split, I
would be faced with the decision of calling the two forks by different
names, or instead treating the land between the two forks as an island
within a single river.  If I lacked the ability to walk downstream a bit to
see if the two forks re-converged, or if they stayed separate all the way to
the ocean, then I would study the local geology and make my best guess as to
whether the water molecules within two forks would ever mix again before
they reached the ocean, then apply the river nomenclature accordingly.

The problem between knowing whether to call two populations distinct
"species" or mere "subspecies" (following the definitions in my previous
posts), is that the correct answer depends on unseen future events. My
advice is to not succumb to "physics-envy" and try to force-fit some sort of
testable objective set of criteria to distinguishing "species" (when that
may very-well lead to obstructions in communication); and instead continue
to perpetuate the use of Linnaean nomenclature in a way that is more or less
consistent with how it has been used for centuries.

Now, I REALLY gotta get some other stuff done tonight!


More information about the Taxacom mailing list