Real species and ideology

[Richard Pyle]

Thanks, Michael.  Am I correct in interpreting your position that you do see
a fundamental distinction between clines and introgression as truly
different processes (by their own essence, independent of an arbitrary
human-defined distinction), and our job is to dicover which process is at
play in any given case?  Or are you saying that clines and introgression are
different points along what is otherwise a single continuum; and our job is
to be more specific in how we define the demarcation between the two, and to
gather sufficient evidence so that we can confidently place each case on one
side of that demarcation or the other?

If the question sounds suspiciously like the one about "species" as
self-evident entities, or merely units in an arbitrarily defined class
system -- that's because it ultimately is the same question.  If there is a
"natural" (i.e., beyond arbitrary human definition) demarcation between
populations that can be identified as distinct species, and populations that
are parts of a conspecific whole; then this demarcation is the same one that
lies between a "cline" situation, and a "hybrid" situation.

Here's a sort of off-the wall question that might better illustrate what I'm
after.  Suppose that our planet was visited by extraterrestrial intelligent
beings about a million years ago, and thes extraterrestrials when about
cataloging the diversity of life on this planet (they would have massively
more advanced technology than we do, and understood the evolutionary process
much better than we do now).  Would their classification system resemble (in
any way) the Linnaean system?  Specifically, would they define a fundamental
unit of sets of organisms that approximates what we think of as "species"?
Or, might their classification system look quite different from Linnaeus'?
Might it be more like PhyloCode? Might it be something altogethr different?
The important question here is whether their system include some sort of
aggregate unit of collected individuals that more or less resembled our
concept of "species"?  If you believe that there is some sort of intrinsic,
"self-evident" boundary or disjunction among organisms that represents the
"species" threshold, then you'd probably guess that they would.

Aloha,
Rich

=======================================================
Richard L. Pyle, PhD
Ichthyology, Bishop Museum
1525 Bernice St., Honolulu, HI 96817
Ph: (808)848-4115, Fax: (808)847-8252
email: deepreef at bishopmuseum.org
http://www.bishopmuseum.org/bishop/HBS/pylerichard.html

> -----Original Message-----
> From: Taxacom Discussion List [mailto:TAXACOM at LISTSERV.NHM.KU.EDU]On
> Behalf Of Michael Bayly
> Sent: Wednesday, April 21, 2004 10:50 AM
> To: TAXACOM at LISTSERV.NHM.KU.EDU
> Subject: Re: Real species and ideology
>
>
> Hi Richard,
>
> The point you make from those scenarios is well taken.  I suppose
> that what I was trying to say is that in those cases where you
> can demonstrate that the two "messy" taxa are not most closely
> related (i.e., there are sufficient extant - or discovered -
> species, and appropriate markers for doing this), then you can
> invoke an explanation of introgression.
>
> If these conditions are not met, then either process
> (introgression/clinal variation) could be responsible for the
> given pattern.
>
> I suppose it is a process of elimination and appropriate genetic
> data could, in some cases, give you a useful answer.
>
>
> cheers,
> Mike
>
> ----------------
> Michael Bayly
> Research Scientist in Plant Biosystematics
> Museum of New Zealand Te Papa Tongarewa
> PO Box 467
> Wellington, New Zealand
> Ph: +644 381 7262
> Fax: +644 381 7070