At any rate I don't think that would have been the kind of speciation that you're looking for anyway. - No, you are correct. I am looking for true speciation. But the issue of mating or not mating is a problem as the definition. After all, we can have tigrons and ligers. Horse and donkey give a mule. - On the Grand Canyon the North Rim squirrels differ from the South Rim variety; at some point the original squirrels were all the same but became separated as the river cut through the rising plateau over a 10 million year period. North Rim at 9,000 feet, South at 7,000. Now exposed to difffering climates, they are different, but I'll bet (without looking it up) they can mate.