If you're the biblically minded sort, then the trouble began when a jealous Cain clubbed Abel to death, but if you're evolutionarily minded, then it's a 'chicken and egg' question. Violence had no beginning, except perhaps in the Big Bang, it was always here, coded into the DNA. If people are just grown-up animals, more articulate versions of the creatures who eat each other's young, and sometimes their own young, there is as much use in wondering about the nature of evil as there is in trying to understand why a killer whale kills. But debating how many devils can...