Rules regulating social behavior raise challenging questions about cultural evolution in part because they frequently confer group-level benefits. Current multilevel selection theories contend that between-group processes interact with within-group processes to produce norms and institutions, but within-group processes have remained underspecified, leading to a recent emphasis on cultural group selection as the primary driver of cultural design. Here we present the self-interested enforcement (SIE) hypothesis, which proposes that the design of rules importantly reflects the relative enforcement capacities of competing parties. (...) We show that, in addition to explaining patterns in cultural change and stability, SIE can account for the emergence of much group-functional culture. We outline how this process can stifle or accelerate cultural group selection, depending on various social conditions. Self-interested enforcement has important bearings on the emergence, stability, and change of rules. (shrink)

The ten original studies included in this Research Topic investigate selected assumptions and predictions of parochial altruism theory in detail. We, the editors, are convinced that their highly instructive findings will help researchers interested in parochial altruism, but also in intergroup psychology more generally, to gain a much more fine-grained understanding of the interplay of altruistic and spiteful motives in human decision making in the context of intergroup relations. The broad range of disciplines represented by the authors contributing to this (...) Research Topic and the variety of methods used in their studies are representative for the current interdisciplinary interest in parochial altruism. The most important insight that, in our view, can be derived from the works collected here is that human decision making in intergroup contexts is more complex than suggested by current theory. Thus, we hope that future theorizing on parochial altruism will be stimulated by the evidence gathered in this Research Topic. In this editorial, we briefly highlight central findings reported here, which, to us, appear most informative for prospective enhancements of parochial altruism theory. (shrink)

Chimpanzees, bonobos, and human foragers share a fission-fusion social system and a mating system of joint male resource defense polygyny. Within-community skew in male strength varies among and within species. In this study, we extend a mathematical model of within-group male coalition formation among primates to derive the conditions for between-community conflicts in the form of raids. We show that the main factor affecting the presence of successful raiding is the likelihood of major discrepancies in party strength, which are set (...) by party size distributions (and thus community size) and the skew in strength. This study confirms the functional similarities between the raiding of chimpanzees and human foragers, and it supports the “imbalance of power” hypothesis for raiding. However, it also proposes two amendments to this model. First, the absence of raiding in bonobos may be attributable more to potential female involvement in defense against raids, which increases the size of defensive coalitions. Second, the model attributes some of the raiding in humans to major contrasts in instantaneous fighting ability created by surprise raids on unarmed victims; it also draws attention to the distinction between minor raids and major raids that involve multiple bands of the same community. (shrink)

De Dreu and Gross's distinction between attack and defense is complicated in real-world conflicts because competing leaders construe their position as one of defense, and power imbalances place status quo challengers in a defensive position. Their account of defense as vigilant avoidance is incomplete because it avoids a reference to anger which transforms anxious avoidance into collective and unified action.

De Dreu and Gross predict that attackers will have more difficulty winning conflicts than defenders. As their analysis is presumed to capture the dynamics of decentralized conflict, we consider how their framework compares with ethnographic evidence from small-scale societies, as well as chimpanzee patterns of intergroup conflict. In these contexts, attackers have significantly more success in conflict than predicted by De Dreu and Gross's model. We discuss the possible reasons for this disparity.

De Dreu and Gross offer a compelling synthesis of a growing literature on the psychology of attack and defense. I argue that human raiding ecology suggests the need to endogenize attacker-defender move order as well as opportunities for tactical mismatch available to defenders. Perhaps most significantly, I draw attention to the surprising lacunae in sex differences across attack and defense.

Building on and partially refining previous theoretical work, this paper presents an extended simulation model of ancestral warfare. This model (1) disentangles attack and defense, (2) tries to differentiate more strictly between selfish and altruistic efforts during war, (3) incorporates risk aversion and deterrence, and (4) pays special attention to the role of brutality. Modeling refinements and simulation results yield a differentiated picture of possible evolutionary dynamics. The main observations are: (i) Altruism in this model is more likely to evolve (...) for defenses than for attacks. (ii) Risk aversion, deterrence and the interplay of migration levels and brutality can change evolutionary dynamics substantially. (iii) Unexpectedly, one occasional simulation outcome is a dynamically stable state of ‘tolerated intergroup theft’, raising the question if corresponding patterns also exist in real intergroup conflicts. Finally, possible implications for theories of the co-evolution of bellicosity and altruism in humans are discussed. (shrink)

Although humans qualify as one of the most cooperative animal species, the scale of violent intergroup conflict among them is unparalleled. Explanations of the underlying motivation to participate in an intergroup conflict, however, remain unsatisfactory. While previous research shows that intergroup conflict increases ‘in-group love’, it fails to identify robust triggers of ‘out-group hate’. Here, we present a controlled laboratory experiment, which demonstrates that ‘out-group hate’ can be provoked systematically. We find direct and causal evidence that the intention to protect (...) the in-group is not only a crucial motivator of ‘out-group hate’ in defensive reactions, but also promotes preemptive offensive actions against out-group threat. Hence, the strength of ‘out-group hate’ depends on whether the own group is perceived to be on the offensive or the defensive side of the conflict. This finding improves our understanding of the escalation of intergroup conflicts and may have important implications for their prevention, as we find in our experiment that removing out-group threat substantially reduces intergroup aggression, leading to full peace. (shrink)

Thermoregulation is often thought to be a key motivating factor behind the origins of clothing. Less attention has been given, however, to the production and use of clothing across traditional societies in contexts outside of thermoregulatory needs. Here I investigate the use of disguises, modesty coverings, and body armor among the 10 hunter-gatherer societies in the Probability Sample Files (PSF) within the Human Relations Area Files (HRAF) World Cultures database, with a particular focus on disguise cases and how they compare (...) with strategies of deception across other taxa. The employment of disguises—defined as altering one’s appearance for purposes of deceiving conspecifics or other animals—is noted for eight of the 10 societies, with their use occurring in contexts of hunting, religious or cult practices, and war or interpersonal violence. Most hunter-gatherer disguises demonstrated clear similarities to cases of visual deception found in other species, with the majority of examples fitting categories of animal mimicry, masquerading as plants, disruptive coloration (camouflage), or background matching (camouflage), while disguises unique to humans involved the impersonation of culture-specific “spirit-beings.” Clothing for modesty purposes (nine societies) and body armor (six societies) are also noted. I propose that strategic initiatives by individuals or groups to disguise or conceal themselves represents one possible initial pathway to the cultural evolution of clothing. There are likely multiple potential (nonexclusive) social and functional pathways to the emergence of clothing outside of thermoregulatory needs. (shrink)

This study tested four theoretical models of leadership with data from the ethnographic record. The first was a game-theoretical model of leadership in collective actions, in which followers prefer and reward a leader who monitors and sanctions free-riders as group size increases. The second was the dominance model, in which dominant leaders threaten followers with physical or social harm. The third, the prestige model, suggests leaders with valued skills and expertise are chosen by followers who strive to emulate them. The (...) fourth proposes that in small-scale, kin-based societies, men with high neural capital are best able to achieve and maintain positions of social influence (e.g., as headmen) and thereby often become polygynous and have more offspring than other men, which positively selects for greater neural capital. Using multiple search strategies we identified more than 1000 texts relevant to leadership in the Probability Sample of 60 cultures from the Human Relations Area Files (HRAF). We operationalized the model with variables and then coded all retrieved text records on the presence or absence of evidence for each of these 24 variables. We found mixed support for the collective action model, broad support for components of the prestige leadership style and the importance of neural capital and polygyny among leaders, but more limited support for the dominance leadership style. We found little evidence, however, of emulation of, or prestige-biased learning toward, leaders. We found that improving collective actions, having expertise, providing counsel, and being respected, having high neural capital, and being polygynous are common properties of leaders, which warrants a synthesis of the collective action, prestige, and neural capital and reproductive skew models. We sketch one such synthesis involving high-quality decision-making and other computational services. (shrink)

Evolutionists studying human cooperation disagree about how to best explain it. One view is that humans are predisposed to engage in costly cooperation and punishment of free-riders as a result of culture/gene coevolution via group selection. Alternatively, some researchers argue that context-specific cognitive mechanisms associated with traditional neo-Darwinian self- and kin-maximization models sufficiently explain all aspects of human cooperation and punishment. There has been a great deal of research testing predictions derived from both positions; still, researchers generally agree that more (...) naturalistic data are needed to complement mathematical modeling and laboratory and field experiments. Most of these data have been obtained from small-scale forager and other societies, but modern intentional communities offer another productive source of information. This exploratory study describes context-specific patterns of punishment in 46 American intentional communities that cast doubt on the prediction that people are predisposed to punish free-riders in naturalistic interactions. (shrink)

Michael Tomasello’s account of moral evolution includes both a synthesis of extensive experimental work done on humans and chimpanzees on their potential for perspective-taking and helpful, altruistic generosity and a major emphasis on “collective intentionality” as an important component of morality in humans. Both will be very useful to the evolutionary study of this subject. However, his disavowal of collective intentions on the parts of chimpanzees would appear to be empirically incorrect, owing to reliance on experimental captive research focused only (...) on dyadic interactions. Here, evidence to the contrary is provided from studies of wild chimpanzees as they naturally cooperate in sizable groups. Collective intentions are inferable when they go on patrol, when they mob predators, when they go hunting, and when large coalitions gang-attack disliked members of the same community. This last behavior has particularly significant pre-adaptive implications for the evolution of moralistic social control, and it suggests that moral evolution has deep roots, going back to the Last Common Ancestor of humans, bonobos, and chimpanzees. (shrink)