>If interbreeding is the sole (or principle) criterion for speciation,
where
>do hybrids come from?  Hybrids should be impossible if species, by
>definition, cannot interbreed.  Are the domestic dog, the wolf and the
>coyote conspecific because they sometimes interbreed?


Interbreeding is generally a basic underlying principle of species
definitions, even in those that do not explicitly mention it (since
those generally refer to a certain level of differentiation which
itself suggests a lack of interbreeding).  However, absolutely zero
interbreeding is not a realistic standard.  Even some forms that seem
to interbreed fairly freely turn out to ultimately have critical
differences.  E.g., the Baltimore and Bullock's Orioles were lumped
into one species, the Northern Oriole, when people found that they
seemed to readily interbreed in the small area of range overlap.
However, long-term studies showed that the hybrids seem not to do quite
as well as purebred individuals, and DNA indicates that the two are
actually not each other's closest relative, much less conspecific.

Of course, interbreeding doesn't help much when dealing with asexually
reproducing taxa, either, and it's often not very practical to test
(extinct species, two individuals of the same sex, difficulties in
proving who is breeding with whom in spawning....)

----------------------------------------
Dr. David Campbell
425 Scientific Collections
University of Alabama, Box 870345
Tuscaloosa AL 35487
"James gave the huffle of a snail in
danger But no one heard him at all"  A.
A. Milne

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