Glowacki identifies social norms as having played an important role in the emergence of both peace and war. Arguably, the emergence of such social norms, and hence of peace and of war, would have been dependent on the cognitive capacity for higher order mentalising, and the role played by this in conflict management merits further consideration.

Dunbar (Reference Dunbar2014) describes a uniquely human cognitive ability to mentalise to multiple orders of intentionality, with one order being self-awareness, second order the ability to infer the mental state of another, third order the ability to infer another's inferences about another's mental state, and so on, with most adult humans being capable of mentalising to between four and five orders (Launay et al., Reference Launay, Pearce, Wlodarski, van Duijn, Carney and Dunbar2015). Although focussing more on the origins of religion and group cohesion, rather than social norms and conflict, Dunbar argues that a cognitive capacity for five orders of intentionality makes possible complex storytelling, enabling the emergence of religion and shared sets of beliefs with a common world view.

A related phenomenon is that of common knowledge (Lewis, Reference Lewis2008) which has been described as a type of recursive mentalising (De Freitas, Thomas, DeScioli, & Pinker, Reference De Freitas, Thomas, DeScioli and Pinker2019), whereby “I know X, and I know that everyone else knows X, and I know that everyone else knows that everyone else knows X,” and so on. As this is limited to just one piece of information, it is less cognitively demanding than the complex storytelling described by Dunbar, thus enabling what are, in effect, infinite orders. Common knowledge can solve coordination problems, including the cooperative dilemmas described by Glowacki, involving conflict suppression and conflict initiation.

However, common knowledge alone neither necessarily entails any moral duty nor imperative, to act in a particular way. Two hypotheses that do, at least implicitly, entail common knowledge about moral imperatives in the context of conflict, are DeScioli and Kurzban's hypothesis on the evolutionary origins of nonconsequentialist morality (DeScioli & Kurzban, Reference DeScioli and Kurzban2013), and René Girard's scapegoat hypothesis on the origins of religion (Girard, Reference Girard1986).

Nonconsequentialist, or deontological, moral thinking is ubiquitous in humans, but as it involves moral imperatives that are independent of outcome, these can often seem maladaptive. DeScioli and Kurzban (Reference DeScioli and Kurzban2013) consider the evolutionary origins of such potentially harmful moral cognitions. They surmise a role in allowing individuals to coordinate which side to take in a conflict, thus making conflicts more decisive and limited, rather than delicately balanced, protracted, and costly. This coordination function relies on there being common knowledge as to what the relevant deontological moral code is, which is, arguably, akin to a social norm.

Girard (Reference Girard1977) speculated that humans are unique in having an unconscious tendency to mimic, or imitate, one another's mental states (a phenomenon he called mimesis). Arguably, this was an emergent property of a cognitive ability to mentalise having developed where there was a preexisting tendency to imitate behaviours, as when a conspecific's mental state can be inferred, it can also be imitated. Although this may have conferred an adaptive advantage in aligning all members of a community towards a common goal, analogous to Tomasello's concept of shared intentionality (Tomasello & Carpenter, Reference Tomasello and Carpenter2007), Girard argued that this would also have been socially destabilising by undermining hierarchical differences, and generating rivalries, as everyone imitated each other's desires. This, he suggested, was one of the main causes of early hominin conflict, or intragroup conflict at least. His scapegoat hypothesis (Girard, Reference Girard1986; Riordan, Reference Riordan2021) posits that such conflict would have been countered by a phenomenon which would itself have been an emergent property of imitation, that is, a tendency to respond to crises, including conflict-related crises, by imitating the blaming of an often arbitrarily selected victim, culminating in their expulsion, or more likely, their killing by mob violence. He suggested that such spontaneous, violent and cathartic events had strong unifying, and thus coordinating effects on communities, and were the origin of mythological, religious, and by extension moral, narratives, as archaic communities may have, post hoc, misidentified the victim as God-like, perceiving them to have both caused and resolved the crisis.

Lewis (Reference Lewis2008) proposes three means by which common knowledge can be generated: Precedent, agreement, and salience. As agreement requires some preexisting system of communication, arguably, only salience can initiate common knowledge de novo. Although Girard did not explicitly refer to the concept of common knowledge per se, the very public, unanimous, and emotionally charged behaviour he envisaged may have provided early human societies with the salience required to generate common knowledge de novo, especially common knowledge about sacred or deontological values and the associated social norms.

I argue that Dunbar's religious narratives that enhance group cohesion, DeScioli and Kurzban's nonconsequentialist moral cognitions that mitigate conflict, and Girard's scapegoat mechanism that generates unanimous sacred values, although distinct hypotheses, with different emphases, have, nevertheless, much in common, and may be describing what is essentially the same phenomenon. That is, the emergence of common knowledge making possible social norms, including, importantly, those social norms, considered by Glowacki, that manage and coordinate peace and war.

Glowacki's observation that the social and cognitive mechanisms that bring peace, can also be used to wage war, is resonant with Girard's posited mechanism that entails violence bringing about peace, as both illustrate the ambiguity between the sources of peace and of war. Common knowledge may have provided not only the means for making peace and war, by solving coordination problems, but also the motivation, by making possible shared deontological or sacred moral imperatives.