I very much like the approach taken here on evolution of peace and the norms and institutions that enforce effective conflict resolution. It is a much needed perspective that ought to be more strongly researched. Far too many articles are narrowly unbalanced as they address the causes, conduct, frequency, intensity (mortality rates), and consequence of war in preindustrial societies. I currently teach a course on the anthropology of war and thanks to Glowacki's comparative research I include some of the material presented here in that course.

In the study of origins of peace, groups such as the Pygmies and southeast Asian societies are often problematically used as evolutionary models of hunter–gatherer peace. As Glowacki and others have argued many of these societies are either strongly tied or have been pacified by more powerful nonforagers or otherwise have had their social system disrupted making war costly (Ember & Ember, Reference Ember, Ember, Martin and Frayer2014, pp. 2–3). More to the point, a historical comparison of groups before pacification (e.g., colonial administration) and after pacification (Ember & Ember, Reference Ember and Ember1994) shows that the frequency of war declined strongly after pacification. Thus the use of postpacification descriptions of preindustrial warfare to understand indigenous cultural factors behind peacemaking is problematic. Glowacki's strong survey of the peacemaking _literature will inspire others to further examine the conditions under which effective conflict resolution practices emerge. To this end, I will focus on lingering problems making the achievement of peace difficult such as resource competition, external warfare, the psychological dimensions of in-group and out-group dynamics, and the warrior complex.

Glowacki states “The key factor is not that a subsistence strategy necessarily yields either war or peace… but rather that social and cultural features constrain and influence behavior by shaping the payoffs associated with war and peace” (target article, sect. 9, para. 3). Although Glowacki notes that competition over scarce resources is a problem, in some instances I feel this may at times be a nearly intractable problem and thus crucial. Comparative research (Allen, Bettinger, Codding, Jones, & Schwitalla, Reference Allen, Bettinger, Codding, Jones and Schwitalla2016; Dow, Mitchell, & Reed, Reference Dow, Mitchell and Reed2017; Ember & Ember, Reference Ember and Ember1992; Kelly, Reference Kelly and Fry2013) shows strong correlations between warfare frequency and intensity and resource competition. I say intractable because in places like highland New Guinea population densities are extremely high (Brown & Podolefsky, Reference Brown and Podolefsky1976) such that agricultural intensification through mounding, mulching, ditching, and so on has perhaps reached its limits given local technology. In a comparison of 26 New Guinea societies Ember (Reference Ember1982) demonstrated a correlation between war and population density. Comparative data also reveal that food producers (pastoralists, horticulturalists, and agriculturalists) have greater frequency of warfare compared to hunter–gatherers (Ember & Ember, Reference Ember, Ember, Martin and Frayer2014; Wrangham, Wilson, & Muller, Reference Wrangham, Wilson and Muller2006). Among hunter–gatherers it is likely the case that the benefits of war in terms of access to low-density resource and unimproved foraging areas is less than that for food producers gaining access to improved and high-density resource areas. Plus those who are attacked are more likely to defend themselves because they are vitally tied to their lands.

Early on Glowacki states he avoids the distinction between internal and external war. I think this is a mistake if we are to understand conflict resolution. Internal war refers to warfare within the same ethnolinguistic group or “cultural unit” (Otterbein, Reference Otterbein and Honigmann1973) while external war refers to war between different cultures. In external war enemies speak different dialects or languages, may have different means for conflict resolution, and so on. Through socialization (Ember & Ember, Reference Ember and Ember1992) these and other differences may ultimately lead to greater fear, hatred, and mistrust of outsiders (Hewstone, Rubin, & Willis, Reference Hewstone, Rubin and Willis2002; McDonald, Navarrete, & Van Vugt, Reference McDonald, Navarrete and Van Vugt2012). In contrast, internal war pit groups who speak the same language, typically intermarry and trade, and may celebrate common religious events. Clearly those groups who speak the same language and follow the same conflict resolution practices are much more likely to be able to negotiate peaceful resolutions of conflict. In a survey of lowland South American warfare Walker and Bailey (Reference Walker and Bailey2013) show that body counts or the number of deaths per conflict is greater in external war (10 deaths) than internal war (3.7 deaths) even though internal war is more frequent (Table 2). In external war they conclude “External revenge raids kill more people on average than the original grievance, indicating a tendency towards escalation in violence and increasingly vicious cycles of revenge killings between ethnolinguistic groups” (Walker & Bailey, Reference Walker and Bailey2013, p. 32). van der Dennen (Reference van der Dennen1995, p. 78) in his comprehensive survey of tribal warfare also notes that external war is more likely to be ethnocentric and genocidal. Whether these generalizations are accurate requires further research.

In the field of social psychology, the distinction between internal and external warfare is directly relevant to the well-studied social psychological literature on out-group and in-group relations and attitudes that appears to be a human universal. Out-groups are easily demonized by in-group members especially in a competitive context (Efferson, Lalive, & Fehr, Reference Efferson, Lalive and Fehr2008). Importantly, classification of out-groups and in-groups can be quickly changed based on common interests (Kurzban, Tooby, & Cosmides, Reference Kurzban, Tooby and Cosmides2001).

Glowacki notes a fundamental conundrum when he states, “Status is almost universally accorded to warriors, providing an important arena for men in the same society to compete with each other for status” (target article, sect. 2.2, para. 1). As he documents, older males who have gained their status through military valor often caution or punish young males who attempt to use the same means to achieve status when they feel hostilities should cease. Thus there is a conflict of interest. This does not mean that older warriors are trying to instill peaceful values after gaining their status through military valor. They may believe that war may not be expedient in certain instances. Presumably, a warrior culture is an adaptive feature in societies where it is found because of the benefits of deterrence and/or acquisition of fitness enhancing resources.