It's strange (at least to me) that many of the answers to Theland's pertinent question are themselves, questions.
Point is, consience, knowledge of right and wrong, care about others is inherent only in the human species. It cannot be demonstrated elsewhere in the animal kingdom. Hence, why only humans? I thas to be attributed to something else other than evolution since, if that behavior were beneficial it woul have developed in othe species.
I would say that Chris' reply is cogent only in that those societies that have developed the ability to exist without (or at least greatly diminished) consience have easily demonstrated what such a society becomes... look no farhter than Nazi Germany.