The nature-versus-nurture debate that pervades psychology, sociology, biology, and other "-ologies" is not likely to be resolved any time soon, lending a distinctly philosophical air to discussions of the two opposing behavioral beliefs. Philosophy is, of course, the centuries-old practice of pondering those lingering questions that may not be definitively answered: the existence of God, for instance, or, in the words of Richard Rhodes, "why they kill," the "they" being violent criminals. In his latest book, the Pulitzer Prize-winning writer, whose previous books have documented such fascinating subject matter as the making of the atomic and hydrogen bombs, delves into a more personal topic: What makes people criminally violent? In his prologue, Rhodes admits to being physically abused for part of his childhood, a trauma experienced to an even greater extent by criminologist Lonnie Athens. It was Athens' radical theory of violent behavior—that individuals become prone to violence through a universal four-step learning pattern—that intrigued Rhodes, but Athens himself proves far more interesting than his theory. The first half of Why They Kill is Athens' biography, which depicts in vivid detail his horribly violent Virginia upbringing as well as his unlikely rise through the ranks of academia. While studying criminology in graduate school, Athens noticed how most studies of violent behavior were based on quantitative rather than qualitative evidence, so he initiated a lengthy, unconventional process of interviewing rapists and murders in person. Athens eventually pinpointed four steps of "violentization": brutalization, belligerency, violent performances, and virulency. Athens theorizes that all violent criminals go through this process, wherein at a young age they are subjected to violence in their primary social group (families, gangs) and quickly learn to resort to violence to get their way. Yet the novel theory is fundamentally flawed in a chicken-and-egg way: If violence is a learned behavior that comes from watching and interacting with others, what violent, nature-spawned individual initiated the centuries-old cycle? Consequently, when Rhodes applies Athens' theory of violentization to a number of famous criminals in the book's second half (Mike Tyson, Lee Harvey Oswald), the exercise seems more interesting than truly eye-opening: Just because most criminals fit the pattern doesn't necessarily make the pattern valid. As for Athens himself, his nurture-minded theory nonetheless offers new ways to perceive violence, as well as a fairly engrossing read.