"Actually I don't distinguish human from animal in any ultimate sense (I'm with both Woj and Ravi on this, oddly enough)."
I think I agree. (Depends on the "ultimate sense" referred to.)
Obviously humans are hardwired with the capacity to rape and murder and commit genocide; it's happened. I agree with Angelus Novus that the key is separating the "ought" of human relations from the "is." (And I think even MLK made some statement that people should separate the "ought-ness" of human society from its "is-ness.") Humans may have evolved to have some traits -- such as an inclination to wage warfare -- but that doesn't mean it's right for them to do so.
In fact, there's a frustrating confusion among a lot of folks between what's morally right and what's "natural." It's natural for humans to kill, apparently (just look at the 20th century), and it's "natural" for them to get malaria and yellow fever and other illnesses. That doesn't mean those things are good. The conflation between "natural" and "good" I think comes from the 19th century, when people stopped invoking God to justify things -- "The wife must submit to the man, because God ordains it" -- and instead began saying "The wife must submit to the man, because that's what nature apparently wants." The fact women were subservient to men seemed like obvious evidence that that was what this diaphanous entity, "nature," intended.
You find the "what nature intends"-type arguments in debates about gays ("homosexuality is not natural") and diets ("vegetarianism isn't natural") where "natural" is conflated with "morally good" or worse, "biologically unavoidable."
-B.