My observations helped me see human behavior in an evolutionary light. By this, I mean not just the Darwinian light one hears so much about, but also the apelike way we scratch our heads if conflicted, or the dejected look we get if a friend pays too much attention to someone else.
At the same time, I began to question what I’d been taught about animals: They just follow instinct; they have no inkling of the future; everything they do is selfish. I couldn’t square this with what I was seeing. I lost the ability to generalize about “the chimpanzee” in the same way that no one ever speaks about “the human.” The more I watched, the more my judgments began to resemble those we make about other people, such as this person is kind and friendly, and that one is self-centered. No two chimpanzees are the same.