The following was originally going to be a top-level post, but I never posted it because I couldn't complete the proof of my assertion.

In his recent book I Am a Strange Loop, Douglas Hofstadter writes:

A spectacular evolutionary gulf opened up at some point as human beings were gradually separating from other primates: their category systems became arbitrarily extensible. Into our mental lives there entered a dramatic quality of open-endedness, an essentially unlimited extensibility, as compared with a very palpable limitedness in other species. Concepts in the brains of humans acquired the property that they could get rolled together with other concepts into larger packets, any such larger packet could then become a new concept in its own right. In other words, concepts could nest inside each other hierarchically, and such nesting could go on to arbitrary degrees. This reminds me—and I do not think it is pure coincidence—of the huge difference, in video feedback, between an infinite corridor and a truncated one.

In other words, Hofstadter sees a phase transition, a discontinuity, a binary division between the mental processes of humans and other species. Yet curiously, when he discusses the moral consideration we ought to give to various species, he advocates a continuum approach based on something like "capacity for friendship", thereby privileging species with K-strategies and/or pack-hunting tendencies for no very good reason that I can see.

To me, the implication of Hofstadter's phase transition is obvious: beings with arbitrary category systems get moral consideration; those with bounded systems do not. By "moral consideration", incidentally, I don't mean some sort of Kantian treating-as-ends-not-means (oh wait, Kant is irrelevant); rather I mean that when you're making some nice utilitarian calculation, you must consider the feelings/opinions of all humans involved, but should not factor in the preferences of (say) a dog.

<proof here attempted to show that we should only give moral consideration to beings capable of giving moral consideration to us>

This is not to say that animal cruelty for the hell of it is a good idea (though I think it should be legal). Many of us anthropomorphize animals, especially pets, to a huge extent, and doing "evil" to animals could easily lead to actual evil. On the other hand, if you're deciding between torturing a human or a googol kittens, go for the kittens.