In the second program, Alda joins researchers studying our fellow simians - mainly chimpanzees, our closest living relatives - to discover both what we share with them and what new skills humans evolved since we went our separate ways. By watching - and participating in - experiments comparing chimps with children, he learns that human uniqueness lies in our ability to reason about things we can't observe, especially the content of others' minds, and to employ this skill in the collaborative enterprise we call civilization.