Of all the tropes which have appeared in the course of man's fetish for fiction, none have created so many inconsistencies as the anthropomorphized animal. It's one thing to imagine a world where animals have completely replaced humans as the dominant life form, and even less confusing when you limit the intelligent animals to a single species or biological class. Often times, however, that's boring as fuck and the creators mix in a variety of species to populate their worlds, sometimes even placing them alongside human beings.
This in itself isn't too bad... but there are a large handful of these worlds where the animals not only exist as and alongside humans, but own pets as well! Sometimes these pets are humorous portrayals of primitive man, to complete the role reversal, but more often than not these pets are more realistic animals. Arthur Read, the most famous aardvark on the planet, owns a pet dog, Sonic the Hedgehog also has a pet dog, Rocko the Wallaby also has a dog. These characters all exist alongside anthropomorphic canines such as Binky Barnes, Lupe the Wolf, and Heffer's adoptive family, the Wolfes, are... wolves.
How can this be legal? In the worlds which take place in alternate Americas, this should be slavery. And just why is it that the designated pet animals are less anthropomorphic than the main characters and surrounding citizens? Just what the hell is going on here?
I believe it must be true that these worlds, all of which seem to adhere to the same biological laws (as do a number of similar franchises, such as Looney Tunes, Ren & Stimpy, and The Angry Beavers) must actually be a part of one larger world which all ties together. Because of this, maybe Sonic Adventure actually provides us with the key piece of information required to finally make sense of this madness.
Browsing Did You Know Gaming earlier today, I stumbled across a little Sonic the Hedgehog trivia I had never known: Chaos, the god of destruction imprisoned within the Master Emerald, is actually a Chao which was mutated by the energy of the Chaos Emeralds. For those who are out of the Sonic loop, Chao are adorable little creatures which basically serve the role of being harmless pet monkeys. They're a race of fictional animals, basically.
But wait, that's interesting insight there. The Chaos Emeralds took a member of an animal race and mutated it into an intelligent, bipedal life form... like every kind of animal character in that franchise, and like every kind of animal character from any other anthropomorphic franchise. Ever. Couldn't it be possible, then, to say that the Chaos Emeralds could have mutated Sonic's ancestors into intelligent beings while leaving regular hedgehogs also in the world? This would not only explain how there are both regular animals and anthropomorphized ones, but it would also explain why there are fewer anthropomorphs than humans (depending, of course, on franchise).
Anyways, that's all just a theory. Just a way to rationalize the irrational to shut my brain off at night.