I've always wondered why so many cartoons, both print and film, used animals as their protagonists. Very often the animals dressed, acted and talked like human beings, or were even caricatured to resemble celebrities. Donald Duck, Mickey Mouse, Porky Pig, the list goes on. These were stars, but very often the walk-ons and cameo roles were assigned an animal persona (cops were usually bulldogs, particularly in print comics). Goofy was a dog portraying a human, but Pluto was never anything but a dog. Only a few, like Bugs Bunny or Woody Woodpecker, were purebred beasts.

Could this have been an effort to include (or exclude!) cultural diversity by making the characters ethnically neutral? Either to avoid offending racial groups, or perhaps to make the cartoons as broadly appealing as possible across all society. I think this is potentially much more sociologically significant than the fact all toons had three-fingured hands, or that Donald Duck never owned a pair of pants.