The thread "Do different human races exist?" got me wondering about this. In any other species, has there ever been any observation or discovery which indicates that two entirely separate chains of evolution have produces two separate species capable of interbreeding? Say, two creatures develop in separate parts of the world, don't have any contact through millions of years of evolution, and now are observed breding, for example. Has there ever been any genetic evidence of observation which would indicate this possibility? It seems to me this question is very important to the question in the other thread I mentioned.