Cruelty is the deliberate infliction of physical or psychological pain on other living creatures, sometimes indifferently, but often with delight. Though cruelty is an overwhelming presence in the world, there is no neurobiological or psychological explanation for its ubiquity and reward value. This target article attempts to provide such explanations by describing three stages in the development of cruelty. Stage 1 is the development of the predatory adaptation from the Palaeozoic to the ethology of predation in canids, felids, and primates. (...) Stage 2, through palaeontological and anthropological evidence, traces the emergence of the hunting adaptation in the Pliocene, its development in early hominids, and its emotional loading in surviving forager societies. This adaptation provides an explanation for the powerful emotions – high arousal and strong affect – evoked by the pain-blood-death complex. Stage 3 is the emergence of cruelty about 1.5 million years ago as a hominid behavioural repertoire that promoted fitness through the maintenance of personal and social power. The resulting cultural elaborations of cruelty in war, in sacrificial rites, and as entertainment are examined to show the historical and cross-cultural stability of the uses of cruelty for punishment, amusement, and social control. Effective violence prevention must begin with perpetrators, not victims. If the upstream approaches to violence prevention advocated by the public-health model are to be effective, psychologists must be able to provide violence prevention workers with a fine-grained understanding of perpetrator gratifications. This is a distasteful task that will compel researchers to interact with torturers and abusers, and to acknowledge that their gratifications are rooted in a common human past. It is nonetheless an essential step in developing effective strategies for the primary prevention of violence. Key Words: compassion; cruelty; entertainment industry; evolutionary psychology; intraspecific killing; pain; predation; punishment; torture; violence prevention. Correspondence:c1 Correspondence to: West Hill House, 6 Swains Lane, Highgate, London N6 6QS, United Kingdom. (shrink)