As you report, Randolph Nesse, a psychologist and researcher in evolutionary medicine at the University of Michigan, Illinois, hypothesizes that the relationship between mild and clinical depression is similar to the one between normal and chronic pain (“Mild and Bitter,” June 27, 2009). Both are warning mechanisms. Pain makes you avoid bodily harm, whereas low mood stops you from pursuing unreachable goals. Most important, he offers a sensible explanation of the exceptional level of clinical depression in America: “People here are often driven to pursue overly ambitious goals, which then can lead to depression.” Interestingly, Henry Miller, a keen observer of both America and Europe, where his Tropic of Cancer was written in the early 1930s, offered the very same hypothesis in his book: “Over there you think of nothing but becoming President of the United States some day. (…) Here every man is potentially zero. If you become something or somebody, it is an accident, a miracle.  (…) But it’s just because the chances are all against you, just because there is so little hope, that life is sweet over here.” Of course, writers are often far ahead of their fellow psychologists.