The big question is, can one chimp watch another chimp swinging in a tree and perceive an instance of “Joy”? That would require the observing chimp to have a purely mental concept and infer the swinging chimp’s intention, making a mental inference. Most scientists assume that mental inference is a core ability of the human mind. So a lot is at stake if apes can do it. We know that monkeys cannot; they can understand what a human is doing but not what he is thinking, desiring, or feeling.
