do you get less and less preferential treatment as you become less and less human?

I'd say so, yeah. It's kind of a tricky function, though, since there are two reasons I'm logically willing to give preferential treatment to an organism: likelyhood of said organism eventually becoming the ancestor of a creature similar to myself, and likelyhood of that creature or it's descendants contributing to an environment in which creatures similar to myself would thrive.