We review early and recent psychological theories of dehumanization and survey the burgeoning empirical literature, focusing on six fundamental questions. First, we examine how people are dehumanized, exploring the range of ways in which perceptions of lesser humanness have been conceptualized and demonstrated. Second, we review who is dehumanized, examining the social targets that have been shown to be denied humanness and commonalities among them. Third, we investigate who dehumanizes, notably the personality, ideological, and other individual differences that increase the propensity to see others as less than human. Fourth, we explore when people dehumanize, focusing on transient situational and motivational factors that promote dehumanizing perceptions. Fifth, we examine the consequences of dehumanization, emphasizing its implications for prosocial and antisocial behavior and for moral judgment. Finally, we ask what can be done to reduce dehumanization. We conclude with a discussion of limitations of current scholarship and directions for future research.

Recent theorizing suggests that the 4Ns - that is, the belief that eating meat is natural, normal, necessary, and nice - are common rationalizations people use to defend their choice of eating meat. However, such theorizing has yet to be subjected to empirical testing. Six studies were conducted on the 4Ns. Studies 1a and 1b demonstrated that the 4N classification captures the vast majority (83%-91%) of justifications people naturally offer in defense of eating meat. In Study 2, individuals who endorsed the 4Ns tended also to objectify (dementalize) animals and included fewer animals in their circle of moral concern, and this was true independent of social dominance orientation. Subsequent studies (Studies 3-5) showed that individuals who endorsed the 4Ns tend not to be motivated by ethical concerns when making food choices, are less involved in animal-welfare advocacy, less driven to restrict animal products from their diet, less proud of their animal-product decisions, tend to endorse Speciesist attitudes, tend to consume meat and animal products more frequently, and are highly committed to eating meat. Furthermore, omnivores who strongly endorsed the 4Ns tended to experience less guilt about their animal-product decisions, highlighting the guilt-alleviating function of the 4Ns.

Philosophers have argued that when people are objectified they are treated as if they lack the mental states and moral status associated with personhood. These aspects of objectification have been neglected by psychologists. This research investigates the role of depersonalization in objectification. In Study 1, objectified women were attributed less mind and were accorded lesser moral status than non-objectified women. In Study 2, we replicated this effect with male and female targets and extended it to include perceptions of competence and pain attribution. Further, we explored whether target and perceiver gender qualify depersonalization. Overall, this research indicates that when people are objectified they are denied personhood

Many people like eating meat, but most are reluctant to harm things that have minds. The current three studies show that this dissonance motivates people to deny minds to animals. Study 1 demonstrates that animals considered appropriate for human consumption are ascribed diminished mental capacities. Study 2 shows that meat eaters are motivated to deny minds to food animals when they are reminded of the link between meat and animal suffering. Finally, Study 3 provides direct support for our dissonance hypothesis, showing that expectations regarding the immediate consumption of meat increase mind denial. Moreover, this mind denial in turn reduces negative affect associated with dissonance. The findings highlight the role of dissonance reduction in facilitating the practice of meat eating and protecting cultural commitments.