The age-old question rears its head once more in the wake of Stand By Me’s twenty-fifth anniversary. I hadn’t thought about this one in a while because the answer always seemed ridiculously obvious to me, even back in the pre-adolescent day when i was reading the Disney comics. (I think they were Gold Key, but i’m not going to look it up.)
Pluto is a regular dog with nominal animal intelligence. Goofy is a higher-evolutionary sentient form that evolved from dogs. Is it morally wrong or suspect for Mickey to keep Pluto as a pet? No, in the same way that people in our world (usually freaky people, admittedly) can keep monkeys or even chimps as pets without being accused of species-dependent slavery.
However, more interesting to me than actually dismissing the question is the larger implication for the evolutionary makeup of the Disney toon world. With sentient creatures having clearly evolved along multitudinous lines (dogs, mice, ducks, cows, horses), the Disney universe is perforce one in which the evolution of consciousness didn’t simply follow one line of speciation (the hominids), but a dozen or more lines simultaneously. Australopithecus mice, cromagnon beagles, neandertal ducks — the Disney world had them all. A kind of evolutionary pressure-cooker.
That doesn’t explain all the races in the Disney ’verse having three fingers, though. The more questions we answer, the less we know.