I agree that when it comes to Animal. He is just that, a personification of all that is our animal nature. I can see Neanderthal in him (although I don't believe in Evolution), it's possible that he's throw-back to then? I can also see, Muppet Monster traits in him...although they are usually more specifically monsterish than Animal.
A lot of people speculate that he is humanoid, the same as Zoot, Floyd, and Marvin Suggs.