Pollution and purity in moral and political judgment

The emotion of disgust is evoked by substances such as urine, vomit, blood, and feces, but—as a growing body of work demonstrates—it also plays a significant role in our moral, social, and political attitudes. Despite this wealth of recent research, the reason for the connection between disgust and these attitudes remains unclear. We review the research linking disgust to moral, social, and political attitudes, and propose that these connections can be parsimoniously explained by disgust’s connection to the behavioral immune system, an evolved motivational system that responds to physical contamination threats. This account also suggests that, contrary to what many researchers have assumed, the link between disgust and morality may be due to the specific content of the acts in question rather than to a more general relationship between disgust and morality. Pollution and purity in moral and political judgment Disgust, an emotion that most likely evolved to keep us away from noxious substances and disease, seems especially active in our moral lives. People report feeling disgust in response to many immoral acts (e.g., Rozin, Lowery, Haidt, & Imada, 1999), make more severe moral judgments when feeling disgusted (e.g., Wheatley & Haidt, 2005), and are more likely to view certain acts as immoral if they have a tendency to be easily disgusted (Horberg, Oveis, Keltner, & Cohen, 2009). Yet despite the wealth of evidence linking disgust and morality, the reason for the link remains unclear. This may be because the bulk of empirical work on the topic has been aimed at simply demonstrating that disgust and moral judgment are connected—a claim that, given the influence of rationalist models of moral judgment such as Kohlberg’s (1969), is novel and surprising. Fewer researchers have attempted to explain why disgust and moral judgment should be so connected (for recent exceptions, see Kelly, 2011 and Tybur et al., 2012). Here, we present an attempt to do so. Our primary claim is that disgust functions as part of a general motivational system that evolved to keep individuals safe from disease. As such, disgust motivates negative evaluations of acts that are associated with a threat of contamination (e.g, norm violations pertaining to food and sex); negative attitudes towards unfamiliar groups who might pose the threat of contamination through physical contact (e.g, outgroups characterized by these norm violations, or who are unfamiliar); and greater endorsement of certain social and political attitudes that minimize contamination risk (such as increased sexual conservatism, reduced contact between different social groups, and hostility towards foreigners). This account provides a theoretical rationale for the observed relationship between disgust and moral judgment, and it is able to unify findings from two literatures that, until now, have been largely separate: research examining the role of disgust in moral judgment, and research examining the effects of pathogen threat on political and social attitudes. One of the conclusions to emerge from this review is that that the link between disgust and morality may be different from what has been assumed by many researchers. Rather than a response to moral violations per se, disgust may instead be linked more generally to judgments about acts, individuals, and groups that pose a pathogen threat. Disgust and moral judgment: Three claims In order to defend this conclusion, it is necessary to first review the evidence linking disgust to moral judgment, and to distinguish between the various ways disgust has been hypothesized to play a role in moral judgment. We have argued previously (Pizarro, Inbar, & Helion, 2011) that researchers have made three distinct claims regarding the relationship between disgust and moral judgment: 1) that the emotion of disgust is a consequence of perceiving moral violations; 2) that disgust serves to amplify judgments of immorality; and 3) that disgust acts as a moralizer, pushing previously nonmoral issues into the moral domain. These claims are not mutually exclusive—all three could be true. However, there are varying degrees of empirical evidence to support each. According to the “disgust as consequence” view, disgust is the emotional output of a certain kind of moral appraisal. For instance, researchers have found that disgust is elicited by violations of moral “purity” (Rozin, Lowery, Imada, & Haidt, 1999), “taboo” moral violations (Gutierrez & Ginner-Sorolla, 2007), or being treated unfairly (Chapman, Kim, Susskind, & Anderson, 2009). On this view, disgust might drive reactions to immorality—for example, by motivating people to reject or distance themselves from those seen as immoral—but does not play a causal role in determining whether an action is seen as immoral. In contrast, the “disgust as amplifier” view characterizes disgust as a causal influence on moral judgment, arguing that the presence of disgust during a moral evaluation makes wrong things seem even more wrong. This is a stronger claim regarding the role of disgust, and has been made by researchers who have experimentally manipulated disgust independently of the act being evaluated, for example by inducing disgust with a post-hypnotic suggestion (Wheatley & Haidt, 2005), with a foul odor, or with disgusting film clips (Schnall, Haidt, Clore, & Jordan, 2008). Finally, the strongest causal claim regarding the influence of disgust on moral judgment is that of “disgust as moralizer.” On this view, morally neutral acts can enter the moral sphere by dint of their being perceived as disgusting. For instance, an act (such as smoking), can move from “unhealthy” to “immoral” if reliably accompanied by the emotion of disgust. This claim has the least empirical support of the three, although it is consistent with the finding that “morally dumbfounded” participants defend their selfadmittedly irrational moral judgments with an appeal to the disgusting nature of an act (Haidt & Hersch, 2001). Our argument here relies primarily on evidence for the disgust-as-consequence and disgust-as-amplifier views, for which the evidence is strongest (see Pizarro, Inbar & Helion, 2011). In particular, the view we will defend here is a combination of these two approaches that takes into account additional research on the specificity of these effects— that disgust is more likely to arise and amplify judgments within a particular domain (namely, when the threat of pathogens is involved).