A long time ago, I got into a very heated argument with somebody about whether animals feel pleasure. I don't think we disagreed really in the particulars -- looking back, I would guess it was more a question where I accepted "pleasure" as a synonym for "feels good" and the other person had different ideas.
I didn't appreciate at the time that this was a well-known and old issue in biology, or that Darwin had written about the problem. So when I saw this article by Robin Nixon on current research into the psychology of emotion in animals, I thought I'd point to it. A short excerpt:
Kent Berridge, a biopsychologist at the University of Michigan, compared the brain activity and facial expressions of animals to that of a more readable creature: human infants. When given something pleasurable to taste, both rats and humans make almost identical mouth shapes and sucking motions. Their brain reactions also mirror one another. If we believe the infant "enjoys" the sweet taste based on her pleasant expression, it follows that the rat likely enjoys it too.
I think that will still be unsatisfying for people who think that "higher" emotions like pleasure really combine more basic feelings with higher cognitive functions like self-awareness and rationality. On the other hand, I'm not sure that we can really cover all humans under that kind of definition -- babies being a good example.
