What does it mean to be human? Why do we feel and behave in the ways that we do? The classic answer is that we have a special kind of intelligence. But to understand what we are as humans, we also need to know what we are like motivationally. And what is central to this story, what is special about human motivation, is that humans want to share with others their inner experiences about the world--share how they feel, what they believe, and what they...