Stanford sets out to answer just one big question: Why do people externalize moral precepts? But in the process he offers an intriguing answer to another, potentially bigger question: Why do people cooperate with each other so much?

One long-standing possible answer to this question has been that people evolved to benefit from the action of indirect reciprocity, whereby people (a) prefer to cooperate with people who have a reputation of being cooperators, and (b) prefer to cooperate when doing so will bolster their own reputations (Nowak Reference Nowak2006). However, it is unclear that eliminating reputational concerns eliminates people's bias towards cooperation (Cooper et al. Reference Cooper, DeJong, Forsythe and Ross1996). Moreover, this framework depends on the likelihood of two independent behavioral preferences being selected for: a preference for cooperators and a preference for behaving in reputation-bolstering ways. Stanford elegantly resolves these issues by noting that a belief that moral demands are real should motivate both a preference for moral action and a preference for moral actors.

This argument is at its most compelling if one imagines that the moral demand that is externalized is directly tied to the fitness of networks of individuals with externalized moral beliefs, such as a moral demand to help or at least not harm others – that is, if externalized morality is in fact externalized prosociality. By contrast, this argument is weakest when it is forced to confront the fact that there appear to be many types of externalized moral demands that do not seem inherently cooperation- or fitness-enhancing. As Stanford acknowledges, work by Haidt and colleagues (e.g., Haidt et al. Reference Haidt, Koller and Dias1993) has revealed that people judge as objectively wrong activities “such as privately washing the toilet bowl with the national flag and privately masturbating with a dead chicken” (target article, sect. 2, para. 2). Stanford subsequently describes these judgments as “partial or incomplete forms of moralization” (sect. 5, para. 12), but it is unclear on what grounds they do not count as fully moral. Although Stanford contextualizes this by noting that moral norms more directly focused on cooperation (e.g., harm and fairness) are more ubiquitous if not universal, it would nonetheless undermine his argument as to the purpose of moral externalization if other forms of morality could readily and equivalently be externalized.

Fortunately for Stanford's argument, there is actually independent evidence that the diverse kinds of moral judgment described by Haidt and others actually may be explainable in terms of the moral imperative to avoid harming others. That is, those who condemn seemingly victimless immoral acts do so in large part because they perceive that there are in fact victims of those acts (Gray et al. Reference Gray, Schein and Ward2014), and perceptions of harm explain nearly all of the intensity of these moral judgments (Gray & Schein Reference Gray and Schein2016; Schein et al. Reference Schein, Ritter and Gray2016). In other words, even moral precepts that do not directly affect others are nonetheless experienced as moral – and perhaps externalized – to the extent that they can be tied to harm. These findings would seem to bolster Stanford's claim that externalized morality evolved in order to facilitate cooperation, but they also suggest a possible refinement to Stanford's proposal: It may not be the case that people externalize moral norms as a whole, but, more specifically, that people externalize the moral imperative to help or at least not harm others.

This idea is intriguing for many reasons, but one reason is that it suggests something genuinely new about the psychology of altruism and cooperation. Psychologists have recognized for quite a while that people engage broadly in altruistic (or, less contentiously, “prosocial”) behavior in part because “it feels like the right thing to do.” However, until now, the best explanation for this sense has been that prosocial behavior is incentivized (and antisocial behavior disincentivized) by social norms that are accompanied by rewards and sanctions (e.g., Cialdini et al. Reference Cialdini, Reno and Kallgren1990). Although these norms and the implied rewards or sanctions can be internalized, it is nonetheless the case that this account of prosocial behavior requires reference to social norms. By contrast, if externalized moral demands have themselves been selected for, per Stanford's account, it is possible that prosocial behavior simply feels right, full stop. This might help explain the finding that prosocial behavior is often automatic and intuitive, and undermined by deliberation (for a review, see Rand Reference Rand2016).

Moreover, perhaps the fact that cooperating or acting prosocially feels right could help explain why it feels good. Acting prosocially predicts greater levels of emotional well-being (Caprara & Steca Reference Caprara and Steca2005; Cialdini & Kenrick Reference Cialdini and Kenrick1976; Dunn et al. Reference Dunn, Aknin and Norton2014) and even predicts increased health and longevity (Brown et al. Reference Brown, Nesse, Vinokur and Smith2003; Poulin & Holman Reference Poulin and Holman2013; Poulin et al. Reference Poulin, Brown, Dillard and Smith2013). It could be that acting in accordance with externalized moral principles confers some of these benefits. The fact that prosocial behavior appears to be most beneficial when offered to others who are believed to be good and trustworthy (Poulin Reference Poulin2014) fits well with the role of externalized morality in coordinating both prosocial behavior and preferences for prosocial others.

Of course, if the benefits of prosocial behavior accrue because of a belief that one is acting on externalized moral principles, this would also suggest that these benefits would not occur for those who failed to externalize the morality of being prosocial. This is at once a testable prediction and a cause for reflection on how humanity's moral nature can fit into modernity. On the one hand, it seems possible we may have evolved to act morally, and enjoy the benefits of doing so, by believing that moral principles are absolute. On the other hand, we have rational reasons to believe that they are not. This tension may be a burden on individuals, and on society.