Why do people find monkeys and apes so compelling to watch? One clear answer is that they seem so similar to us--a window into our own minds and how we have evolved over millennia. As Charles Darwin wrote in his Notebook, "He who understands baboon would do more toward metaphysics than Locke." Darwin recognized that behavior and cognition, and the neural architecture that support them, evolved to solve specific social and ecological problems. Defining these problems for neurobiological study, and conveying neurobiological results to ethologists and psychologists, is fundamental to an...