A long tradition of research has linked morality to cooperation. Cross-cultural data suggest that, wherever people make moral condemnations, they appeal to cooperative rules such as fairness, helping one's group, and reciprocating prosocial behavior (Curry, Mullins, & Whitehouse, Reference Curry, Mullins and Whitehouse2019). Fitouchi et al. show that even many non-harmful behaviors are moralized because they are viewed as inconsistent with self-control, and hence are detrimental to cooperation.

They note that people sometimes use morality for self-interested purposes. Much of the research examining self-interested uses of morality has focused on how people use morality to protect one's mating interests, for example by moralizing behavior associated with sexual promiscuity (Karinen, Wesseldijk, Jern, & Tybur, Reference Karinen, Wesseldijk, Jern and Tybur2021; Kurzban, Dukes, & Weeden, Reference Kurzban, Dukes and Weeden2010; Pinsof & Haselton, Reference Pinsof and Haselton2016) or by advocating for institutional protections against promiscuity in the form of religion (Moon, Reference Moon2021; Weeden, Cohen, & Kenrick, Reference Weeden, Cohen and Kenrick2008). They view this approach as consistent with their own, but as limited in explaining puritanical morality.

However, other puritanical moral judgments can also serve self-interest beyond their benefits to cooperation. Because moral principles are culturally universal, placing one's appeal within a moral principle is likely to be an effective way to advocate for one's own interests. For example, vulnerable individuals – who lack the means to protect themselves or recover from harm inflicted by others – rely more heavily on the cooperation of others; given that cooperation relies on self-control, these are precisely the people who should benefit from puritanical moral norms.

Consistent with this prediction, past research has shown that people who lack material resources (Pitesa & Thau, Reference Pitesa and Thau2014), have weak coalitions (Petersen, Reference Petersen2013), or are exposed to unpredictable environments (Ding & Savani, Reference Ding and Savani2020) tend to favor harsher moral judgments against harmful or exploitative behavior. Similarly, physically weak individuals, who are presumably less able to gain resources by force, tend to favor more egalitarian and peaceful moral principles (Sell, Tooby, & Cosmides, Reference Sell, Tooby and Cosmides2009), in which they are less likely to find themselves at the bottom of a hierarchy.

Another way puritanical morality can serve self-interest is through signaling. As the authors note, signaling one's ability and willingness to delay gratification helps gain others’ trust. This is consistent with the authors’ cooperative account, but people may use puritanical morality to signal qualities for non-cooperative reasons – such as to attract romantic partners (cf. Brown, Keefer, Sacco, & Brown, Reference Brown, Keefer, Sacco and Brown2022) or to gain status. Thus, people might endorse puritanical moral norms partly for the benefits they receive by communicating positive traits about themselves, in addition to their concerns for cooperation.

It may seem odd that any individuals would be willing to sacrifice cooperative norms, but moralization has several costs. In addition to the costs of punishing other people's behavior, moralizing limits one's own behavior (at the risk of being labeled a hypocrite). If such individuals want to engage in gluttony or sexual taboos, moral disciplining requires these opportunity costs. Further, strict moral norms have other cultural implications – they might facilitate a more orderly society, but hinder creativity (Jackson, Gelfand, De, & Fox, Reference Jackson, Gelfand, De and Fox2019). Within a given society, those who are less vulnerable to disorder are more likely to benefit from increased creativity and freedom, and the increased self-control and cooperation gained by moral disciplining are less likely to be worth the costs.

Future research can test whether moral disciplining reflects these types of self-interest by exploring the costs and benefits of moral disciplining for different groups. If moral disciplining serves self-interest, one might expect people in vulnerable states to endorse more puritanical morality. As noted above, vulnerable individuals are generally harsher moral judges (Ding & Savani, Reference Ding and Savani2020; Petersen, Reference Petersen2013; Pitesa & Thau, Reference Pitesa and Thau2014), but this research has generally looked at judgments toward general cooperative domains rather than puritanical moral judgments.

Further, if people use puritanical morality to signal qualities about themselves, one might expect endorsement of puritanical morality to track one's incentives to signal self-control to others. They might do this for cooperative benefits, but perhaps amplify these judgments when there are potential reputational gains. Irons (Reference Irons and Nesse2001) similarly proposed that people engage in religious costly signals to signal cooperative qualities to others, as well as qualities as a prospective mate. People who encounter strangers more frequently benefit by having the means to communicate their trustworthiness quickly; these people therefore tend to be more devout in general, and may even increase their devoutness when they are likely to encounter strangers.

Another line of inquiry might explore how cultural or ecological factors influence puritanical morality. As the authors discuss, cultural evolution might lead to more puritanical morality in societies where cooperation is especially crucial. However, these pressures might also provide opportunities to examine self-interested uses of morality. For example, puritanical moral positions might be more or less useful or powerful in influencing other people's behavior in some societies (Moon, Tratner, & McDonald, Reference Moon, Tratner and McDonald2022), or might make it more important to maintain a good reputation (Awad, Dsouza, Shariff, Rahwan, & Bonnefon, Reference Awad, Dsouza, Shariff, Rahwan and Bonnefon2020). A self-interested perspective would predict that endorsement of puritanical morality will track the costs and benefits, and that this may happen in nuanced ways.