"Monfils, Paul" wrote:

> 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?

* you'll note that my criterion was: "form a single population when
they're in contact:" a hybrid swarm with a unimodal character
distribution, so that there aren't modes representing unhybridized
parental species in the intergrade population. This is the standard
Mayrian criterion for the biological or polytypic species concept, and
it's inferred (assuming one doesn't have direct data on paternitiy) only
from the pattern of variation, not on the basis of its magnitude.

See: Schueler, Frederick W., and James D. Rising. 1976. Phenetic
evidence of natural hybridization.  Systematic Zoology 25:283-289.  I
know less demanding species concepts are now prevalent, but I haven't
followed the relevant literature closely in recent decades.

fred.
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