Behavioral and Brain Sciences

Here we revise Glowacki's model by proposing a simple and empirically tested mechanism that is applicable to a comprehensive set of social interactions. This parsimonious mechanism accounts for the choice of both cooperative and peaceful alternatives and explains when each choice benefits the interacting parties. It is proposed that this mechanism is key to the evolution of both peace and conflict.

The target article offers a game-theoretical analysis of primitive intergroup aggression (i.e., raiding) and discusses difficulties in achieving peace. We argue the analysis does not capture the actual strategy space, missing out "do-nothing." Experimental evidence robustly shows people prefer doing nothing against out-group members over cooperating with/attacking them. Thus, the target article overestimates the likelihood of intergroup aggression.

The emergence of social norms would have been dependent on the evolution of the cognitive capacity for mentalising to multiple orders of intentionality. Common knowledge is a related phenomenon that can solve coordination problems. That the same cognitive and social mechanisms should facilitate both peace and war is resonant with Girard's scapegoat hypothesis on the relationship between violence and religion.

I challenge the idea by Glowacki that "strong sanctions" such as fines, physical punishment, or execution are more effective in promoting peace than "weak punishments" like social rejection. Reviewing evidence that social rejection can have significant social and psychological costs for norm violators, I propose that social rejection can serve as a powerful reputational sanction in fostering peace in society.

If group norms and decisions foster peace, then understanding how norms and decisions arise becomes important. Here, we suggest that neither norms nor other forms of group-based decision making (such as offering restitution) can be adequately understood without simultaneously considering (i) what individual psychologies are doing and (ii) the dynamics these psychologies produce when interacting with each other.

The capacities required for both peace and war predate 100,000 years ago in the genus Homo are deeply entangled in the modes by which humans physically and perceptually construct their worlds and communities, and may not be sufficiently captured by economic models.

The 30 commentators are largely sympathetic to the account I develop for the origins of peace in humans, though many suggest that peace has deeper roots and that humans share characteristics of peace with other species. Multiple commentators propose how to extend my framework or focus on the cognitive and psychological prerequisites for peace. In my reply, I discuss these considerations and further my account of why I think peace as defined here was unlikely prior to behavioral modernity which emerged approximately 100,000 years ago...

Glowacki argues that the human capacity for peace emerged 100,000 years ago, and that the logic of peace is such that the traits and technologies that enable peace are the same that are used to wage war. In my commentary I raise some concerns about these points as well as about Glowacki's understanding of peace.

Although Glowacki proposed that peace developed from the relatively recent advent of intergroup norms and tolerance for out-group members, we submit that (a) positive intergroup relations developed from a psychology grounded in the regulation of intragroup relations, (b) the "default" intergroup orientation is uncertainty, and (c) positive intergroup relations likely existed early in our evolutionary history.

Glowacki's account overlooks the role of religion in the regulation of cooperation, tolerance, and peace values. We interrogate three premises of Glowacki's argument and suggest that approaching religion as an adaptive system reveals how religious commitments and practices likely had a more substantial impact on the evolution of peace and conflict than currently presumed.

Peace, the article shows, is achieved by culturally evolved institutions that incentivize positive-sum relationships. We propose that this insight has important consequences for the design of human social cognition. Cues that signal the existence of such institutions should play a prominent role in detecting group membership. We show how this accounts for previous findings and suggest avenues for future research.

Enhanced cooperation increases the capacity for humans to engage in large-scale warfare. This ability provides the foundation for male coalitionary behavior, leaving open the question of whether cooperation evolved in the same way, or for the same purpose, in females. Such coalitionary behavior entrains hierarchical forms of leadership that remain inherently unstable, providing a spark for conflict to emerge.

We elaborate on Glowacki's claim that humans are more capable of establishing peace than other mammals. We present three aspects suggesting caution. First, the social capabilities of nonhuman primates should not be underestimated. Second, the effect of these capabilities on peace establishment is nonmonotonous. Third, defining peace by human-centered values introduces a fallacy.

Glowacki offers many new directions for understanding and even eliminating the problem of war, especially creating positive interdependencies with out-group members. We develop Glowacki's intriguing proposition that in-group dynamics provide a route to peace by describing a prosocial motivational system, the caregiving system, that aligns individual interests and eliminates the need to use coercion to achieve mutually beneficial outcomes.

Glowacki asserts that interdependent relationships beyond group boundaries are exceptionally rare among nonhuman mammals. However, rudimentary forms of interdependence can be seen in primate species that form multilevel societies, that is, core social units embedded within higher-level grouping categories. Studies of primate multilevel societies can enrich discussions about the evolutionary origins of peaceful between-group interactions in humans.

Glowacki explored the conditions required for peace and argued its preconditions arose only within the last 100,000 years. The present commentary addresses some major brain changes that occurred only in Homo sapiens within that period of time and the verbal and nonverbal cognitive sequelae of those neurological changes that may have aided the diplomatic negotiations required for peaceful solutions.

Based on evidence of selection against alpha-male behavior in the earliest Homo sapiens , I suggest that by 300,000 ya (years ago) language would have been sufficiently sophisticated to contribute to peacemaking between groups. Language also influenced the social landscape of peace and war, and groups' ability to form coalitions.

Economic games provide models of real-world contexts in which researchers can probe dispositional and structural determinants of intergroup relations. Most intergroup games focus on determinants of aggression between groups and constrain the possibilities for peace. However, paradigms such as the intergroup parochial and universal cooperation game allow for peaceful intergroup relations and can be adapted for the study of peace.

Glowacki discusses how humans regularly face collective action problems that may result in either peaceful or aggressive between-group interactions. Peace and war probably coevolved in humans. Using a gene-culture evolutionary framework is a powerful way to analyse why, when, and how humans have the capacity to build and maintain long-term peaceful interactions between groups and also to wage deadly wars.

Glowacki's work meshes well with our view of human nature as having evolved to use culture to improve survival and reproduction. Peace is a cultural achievement, requiring advances in social organization and control, including leaders who can implement policies to benefit the group, third-party mediation, and intergroup cooperation. Cultural advances shift intergroup interactions from negative-sum (war) to positive-sum (trade).