A DEBATE HAS been raging for years between people who believe that most behavior problems result from heredity and those who think these problems have environmental causes. This debate has spilled over into the area of treating illnesses of the mind such as depression. Those who blame heredity for causing illness believe that the genes—the building blocks that determine our physical characteristics—we inherit from our parents also determine our personalities and the ways we think, feel, and act. Those who fault environment, on the other hand, believe that what happens to us early in life—especially the way we are treated by our parents and other adults—is a more important influence on our feelings and behavior. It is difficult to prove either theory. The human mind cannot be examined as easily as a...