Also, Chihuahuas can still mate with other small dog breeds, can't they?
Also, what would become of Chihuahuas and Great Danes if we stopped selective breeding? Wouldn't the extremes of dogkind fade over time?
BTW, I want to add my voice to those who have praised these posts for being free of name calling! And Stremba, if you read this, please don't take my occasional stubbornness for disrespect! :-)
Sure. But we'd have to say the same of any micro-evolutionary process, guided or not. After all, the only difference between "natural selection" and "selective breeding" is the method of selection. If evolution is true, then we would have to grant the possibility of re-convergence, as well as divergence. In essence, for speciation to occur, the theory of evolution would seem to rely on strict separation that would prevent such reconvergence.
Now -- if you took an island-full of Great Danes, and a different island-full of Chihuahuas, you'd have a situation where two breeds were on divergent paths. Would you predict that the breeds on each island would regress to some similar "average dog," or would you instead predict continued divergence?
I would predict the latter -- chihuahuas becoming, say, more weasel-like in response to their probable rodent diet; and the morphology of great danes depending on whatever common food source was on their island.
Note, BTW, that this hypothetical is an example of how intelligent intervention and natural processes might combine. Even though it would be human-initiated, it does not seem clear that some future scientist would be able to find "scientific" evidence of that actual fact. Instead, our future scientists could no doubt find all sorts of "natural" (and wrong) explanations for these two different populations.