In 1971, at the age of seventeen, for reasons unknown to me then or now, I began to keep a journal on human behavior. I catalogued all sorts of “nonverbals”—what is more generally called body language. At first it was the quirky things people did: why did they roll their eyes when they were disbelieving or reach for their neck when they heard bad news? Later it became more nuanced: why did women play with their hair while on the phone or arch their eyebrows when they greeted one another? These were small actions, but they captured my curiosity. Why did humans do such things, in such variety? What was the purpose of these behaviors?