need suggestions

Curtis Clark jcclark at CSUPOMONA.EDU
Fri Jan 5 09:30:10 CST 1996

At 09:47 AM 1/5/96 +0100, Hubert Turner wrote:
>D.J. Kornet, from Leiden University, has proposed a species concept based


>As a corollary of this species concept it follows that species cannot
>hybridize, because that would violate the first criterion of permanent

Hybridization does not always invalidate a "permanent split in the
genealogical network".  As a first example, consider mules.  Since they are
sterile, no gene transfer between species can occur.  But even if hybrids
are fertile, that doesn't ensure gene transfer.  Ledyard Stebbins once told
me after a seminar that my Encelias were a "comparium" (he meant more a
syngameon, in Verne Grant's sense) just like oaks, and that eventually the
species would merge back together.  There are two oaks that hybridize in
California (I can't remember the species offhand) that have fossil records
back to the late Oligocene, and there are even fossils of apparent hybrids
from the Miocene, and yet in 30-odd million years they haven't merged back
together, or even blurred the boundaries much.

Dr. Kornet's theory sounds to me like a mathematical restating of the
syngameon concept (I'm basing this only on the Taxacom account), which just
doesn't work, at least not for flowering plants (which are notorious
hybridizers).  It is genetically immaterial to a species whether it *could*
interbreed out of existence, unless it *does*.  The theory also does not
account for lateral gene transfer, by viruses, bioengineers, ot whatever.
If it were shown that a plant had a gene laterally transfered from an animal
(or vice-versa), would the whole top of the eukaryote tree become a
"composite species"?  And yet if lateral transfer is discarded from
consideration, how would we account for situations where it has cause more
gene exchange than hybridization?

Curtis Clark
Biological Sciences Department                     Voice: (909) 869-4062
California State Polytechnic University, Pomona    FAX:   (909) 869-4396
Pomona CA 91768-4032                               jcclark at

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