Subject: Re: species concepts (was VCR Fox Sparrows)
Date: Jun 17 04:24:32 1995
From: Joe Morlan - jmorlan at slip.net


David Wright wrote:

> But as I mentioned in a previous message, the BSC has big
> problems even if you choose reproductive isolation as the
> most important aspect of speciation. These problems with the
> BSC were not recognized by its architects because they simply
> were not all that concerned with genealogic relationships
> *among* species. That, of course, is at the heart of the
> cladistic revolution, and it is this revolution that led to
> critical reappraisal of the BSC. If the BSC was revamped so
> that it did not produce genealogically nonsensical species,
> it would look a lot like a PSC that takes into account
> population genetics (cf. Donoghue's version of the PSC), and
> a lot like Wiley's ESC. Everything that rises must converge.

There is still a very serious problem with the PSC which David has failed
to address. The PSC fails to provide a framework for polytypic species.
The original morphological species concept gave a separate name for each
morphologically diagnosable population. The PSC brings us back full
circle to the 19th century. The great power of the biological species
concept was to provide a framework for describing intraspecific
geographical variation. The PSC recognizes the tips of the branches of
every single subspecies of Downy Woodpecker or Song Sparrow as an
independent species and provides no nomenclatural basis for pointing out
that they are really just varieties of a single gene pool with extensive
hybridization in many areas.

Furthermore, the PSC has the same problems when it comes to clinal
variation that the biological subspecies does. Where do you draw the
line? My understanding of the Zink & McKittrick proposal is that a
conscientious application of the "extra barbule on the 7th feather"
criterion is that clinal variation demands recognition of an infinite
number of full phylogenetic species. Clearly an impossibility.

The last time we discussed this issue on BirdChat, Paul DeBenedictis wrote:

> There are more ominous implications of these viewpoints as
> well. The 2nd issue of the Proc. of the Nat. Acad. of Sci.
> (USA) for 1995 has a paper comparing the complete
> mitochondrial DNA sequences of the great apes with three human
> populations. The tree below summarizes approximately the
> diferences (percent of DNA changed) found as a genealogy.
>
> |---------------------- chimpanzee
> --| (from other great apes)
> | |----------- African human
> |----------|
> | |--------- Japanese human
> |-|
> |--------- Caucasian human

I pointed out that this result would require recognition of three species
of humans and asked the proponents of the PSC if this is really the
direction they want to go.

Thus far, my question remains unanswered.

----------
Joe Morlan
Albany, CA
jmorlan at slip.net