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 emotionshigh arousal and strong affectevoked 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.

Dispassionate cruelty and the euphoria of hunting or battle should be distinguished from the emotional savoring of victims' suffering. Such savoring, best called negative empathy, is what puzzles motivational theory. Hyperbolic discounting theory suggests that sympathy with people who have unwanted but seductive traits creates a threat to self-control. Cruelty to those people may often be the least effortful way of countering this threat.

In this commentary, I review diverse lines of research conducted at both the macrosocial and microbehavioral level that dispute the view that cruelty is inherently gratifying. Expressions of pain and suffering typically inhibit rather than reinforce cruel conduct in humans. With regard to functional value, cruelty has diverse personal and social effects, not just the alluring benefits attributed to it.

There are few commonalities between intraspecific aggression and predation and few convincing arguments for the conceptualisation of blood and pain as rewards for predation. Not cruelty, but ritualised intraspecific aggression is the predominant mechanism of accretion of social power and this, not cruelty, is what bestows reproductive advantages. Enjoyment of media cruelty is not reinforced by emotional circuits adapted to predation, but represents transient relief from culturally determined inhibition of aggression.

Nell restricts cruelty to hominids, although good evidence suggests that secondary aggression in rodents and particularly primates may be considered cruel. A considerable literature shows that glucocorticoid secretion stimulated by stress facilitates learning, memory, arousal, and aggressive behavior. Either secondary aggression (to a conspecific) or increased affiliative behavior reduces stressor-induced activity, suggesting the reward system can be satisfied by other behaviors than cruelty.

Aggression, violence, and cruelty are symptoms of psychiatric illness. They reflect abnormalities in the regulation of the stress and emotion circuitries. The functioning of these circuitries depends upon the interaction between genetics and environment. Abuse and neglect during infancy, as well as maternal stress and poor quality of maternal care, are some of the causes that produce these types of abnormal behavior. Research on the neurobiological bases of emotion regulation will allow the detection of the population at risk.

The impulse toward violence and cruelty is endemic to the human species. But so, likewise, is the impulse toward compassionate behavior. Victor Nell acknowledges this, but he does not explore the matter any further. I supplement his account by discussing how compassion, specifically in the moral education of children, can help remedy the problem of violence and cruelty in society.

Presentation of evidence from multiple disciplines is the most impressive feature of Nell's article. I have observations and objections, however, about the following issues: (1) violence as a by-product of cruelty; (2) the equation of animal and human cruelty; (3) social psychological evidence contrary to the biological model; (4) whether prevention of cruelty best arises from predispositional or situational factors.

Recent findings in anthrozoologythe study of humananimal interactionsshed light on psychological and social aspects of cruelty. Here we briefly discuss four areas that connect animal cruelty and cruelty directed toward humans: (1) voices of perpetrators and their audiences, (2) gender differences in cruelty, (3) cruelty as play, and (4) the putative relationship between animal abuse and interpersonal violence.

Research on aggression and terror management theory suggests shortcomings in Nell's analysis of cruelty. Hostile aggression and exposure to aggressive cues are not inherently reinforcing, though they may be enjoyed if construed within a meaningful cultural framework. Terror management research suggests that human cruelty stems from the desire to defend one's cultural worldview and to participate in a heroic triumph over evil.

Nell proposes another myth about human aggression, following thousands of old myths from Homer to Lorenz. Like all myths, this one might be partially true and partially false. However, the use of emotional and propagandistic effects, rather than evaluation of empirical results, obscures any attempt to describe the truth about cruelty.

It is full of sound and fury, signifying nothing. Macbeth, Act 5, Scene 5

Cruelty is evident in the play and interactions of quite small children. This is almost certainly normal, though it is more evident in children who have themselves been harshly treated (Amato & Fowler 2002; Luk et al. 1999).

Functional neuroimaging studies allow examination of the cerebral networks involved in human behavior. For pathological aggression, several studies have reported a involvement of frontal and temporal areas, reflecting disruption of emotional regulatory systems. Recent genetic studies that bring together reward system dysfunction and violent behavior.

Cruelty does not emerge from a single emotional system of the brain. Its many cognitive aspects are intermeshed inextricably with the nature of negative affects ranging from fear to suffering. The rewards of cruelty may be counteracted by a variety of neurochemical factors as well as novel social policies.

Intraspecific aggression (IA), in service to dominance, has far deeper roots in animal behavior and human evolution than does predation. The reinforcing properties of such aggression are most likely to be a major source of human cruelty.

Fostering shame in societies may not curb violence, because shame is alienating. The person experiencing shame may not care enough about others to curb violent instincts. Furthermore, men may be less shame-prone than are women. Finally, if shame is too prevalent in a society, perpetrators may be reluctant to talk about their actions and motives, if indeed they know their own motives. We may be unable accurately to discover how perpetrators think about their own violence.

Human beings, like chimpanzees, deliberately kill their own species in order to expand their territory. For a self-aware social animal to attack its own kind, it would need to evolve a mechanism to dehumanize, or dechimpanzee-ize those it attacks. It is suggested that cruelty reflects such an evolved predisposition. The implications for violence prevention are discussed.

The definition of cruelty used by the author is broad and ambiguous and does not distinguish between acts of sadism, abuse, and neglect that all lead to the suffering of other beings. Some of the research involving animal cruelty is reviewed with the aim of raising questions about the relevance of the painblooddeath (PBD) complex described by Nell.

Aggressive-sadistic personality disorder (SPD) involves derivation of pleasure from another's physical or emotional suffering, or from control and domination of others. Findings from a head-injured sample indicate that SPD traits are associated with neuropsychological deficits in executive function and language, suggesting difficulties in frontal-lobe-mediated self-regulation of aggressive and emotional impulses. Implications for rehabilitation of aggressive offenders are discussed.

In the target article, human cruelty is linked to intrinsic reinforcement from engaging in the behavior without any recommendations for a research program to validate or test for such reinforcement and its independence from ultimate adaptive outcomes. Suggestions are offered in this commentary for such a program.