rewarding experiences. Some actions have benign or even beneficial consequences for the welfare of others, while others have malignant and costly consequences. Exquisite studies pioneered by the American cognitive neuroscientist Kent Berridge have uncovered the core elements of pleasure, including distinctive systems of wanting, liking and learning. We, and hundreds of other species, often want things we like, and like things we want. This is, obviously, an adaptive coupling. Thanks to experiments at the level of genes, neurons, and behavior, we can tease apart these three systems. Thanks to naturally occurring situations, we can watch these systems come unglued over the course of addictions, leading to the paradoxical and maladaptive situation of wanting more and more, but liking the experience less and less. Addictions, as archetypal examples of excess, provide a model for thinking about evil and its trademark signature of excessive harm. The paradoxical decoupling between wanting and liking is seen most clearly in studies of obesity in rats and humans, where individuals develop skyrocketing desires for food, but fail to experience comparable pleasure from eating. By definition, those who become obese are prone to eat in excess. One reason they do is because eating, or even seeing images of food, no longer delivers the same honey hit to the brain as in their pre-obesity days. The reward system turns off when we turn to excess. This is adaptive because nothing in excess is good. But because the wanting system runs independently, the adaptive response by the liking system has the unfortunate consequence of making us want more even though we enjoy it less. The proposal I develop in this book is that the same process is involved in evil, especially its expression of excessive harm. It is a process that is aided by denial. Everyone engages in denial, negating certain aspects of reality in order to manage painful experiences or put forward a more powerful image. But