While some species have affiliative and even cooperative interactions between individuals of different social groups, humans are alone in having durable, positive-sum, interdependent relationships across unrelated social groups. Our capacity to have harmonious relationships that cross group boundaries is an important aspect of our species' success, allowing for the exchange of ideas, materials, and ultimately enabling cumulative cultural evolution. Knowledge about the conditions required for peaceful intergroup relationships is critical for understanding the success of our species and building a more (...) peaceful world. How do humans create harmonious relationships across group boundaries and when did this capacity emerge in the human lineage? Answering these questions involves considering the costs and benefits of intergroup cooperation and aggression, for oneself, one's group, and one's neighbor. Taking a game theoretical perspective provides new insights into the difficulties of removing the threat of war and reveals an ironic logic to peace – the factors that enable peace also facilitate the increased scale and destructiveness of conflict. In what follows, I explore the conditions required for peace, why they are so difficult to achieve, and when we expect peace to have emerged in the human lineage. I argue that intergroup cooperation was an important component of human relationships and a selective force in our species history beginning at least 300 thousand years. But the preconditions for peace only emerged in the past 100 thousand years and likely coexisted with intermittent intergroup violence which would have also been an important and selective force in our species' history. (shrink)

People live in distinct groups, notably territory-holding societies, whose boundaries aren't neatly defined by the traits that Pietraszewski describes for his socially aligned groups (or SAGs), as I propose calling them, which occur both within and between our societies. Although studying SAGs could prove enlightening, societies are essential human groups that likely existed long before the complex SAGs of today.

Evolutionary models consider hunting and food sharing to be milestones that paved the way from primate to human societies. Because fossil evidence is scarce, hominoid primates serve as referential models to assess our common ancestors’ capacity in terms of communal use of resources, food sharing, and other forms of cooperation. Whereas chimpanzees form male-male bonds exhibiting resource-defense polygyny with intolerance and aggression toward nonresidents, bonobos form male-female and female-female bonds resulting in relaxed relations with neighboring groups. Here we report the (...) first known case of meat sharing between members of two bonobo communities, revealing a new dimension of social tolerance in this species. This observation testifies to the behavioral plasticity that exists in the two Pan species and contributes to scenarios concerning the traits of the last common ancestor of Pan and Homo. It also contributes to the discussion of physiological triggers of in-group/out-group behavior and allows reconsideration of the emergence of social norms in prehuman societies. (shrink)

What is the relationship between war propaganda and nationalism, and what are the effects of each on support for, or participation in, violent acts? This is an important question for international criminal law and ongoing speech crime trials, where prosecutors and judges continue to assert that there is a clear causal link between war propaganda, nationalism, and mass violence. Although most legal judgments hinge on the criminal intent of propagandists, the question of whether and to what extent propaganda and nationalism (...) interact to cause support for violence or participation remains unanswered. Our goal here is to contribute to research on propaganda and nationalism by bridging international criminal law and the behavioral and brain sciences. We develop an experiment conducted with Serbian participants that examines the effects of propaganda as identified in the latest international speech crime trial as causing mass violence, and thereby test hypotheses of expert witness Anthony Oberschall’s theory of mass manipulation. Using principal components analysis and Bayesian regression, we examine the effects of propaganda exposure and prior levels of nationalism as well as other demographics on support for violence, ingroup empathy, and outgroup empathy. Results show that while exposure to war propaganda does not increase justifications of violence, specific types of war propaganda increase ingroup empathy and decrease outgroup empathy. Further, although nationalism by itself is not significant for justifying violence, the interaction of increased nationalism and exposure to violent media is significant for altering group empathies. The implications of these findings are discussed with respect to international criminal law and the cognitive science of nationalism. (shrink)

Despite remarkable empirical and methodological advances, our theoretical understanding of the evolutionary processes that made us human remains fragmented and contentious. Here, we make the radical proposition that the cultural communities within which Homo emerged may be understood as a novel exotic form of organism. The argument begins from a deep congruence between robust features of Pan community life cycles and protocell models of the origins of life. We argue that if a cultural tradition, meeting certain requirements, arises in the (...) context of such a “social protocell,” the outcome will be an evolutionary transition in individuality whereby traditions and hominins coalesce into a macroscopic bio-socio-technical system, with an organismal organization that is culturally inherited through irreversible fission events on the community level. We refer to the resulting hypothetical evolutionary individual as a “sociont.” The social protocell provides a preadapted source of alignment of fitness interests that addresses a number of open questions about the origins of shared adaptive cultural organization, and the derived genetic adaptations that support them. Also, social cooperation between hominins is no longer in exclusive focus since cooperation among traditions becomes salient in this model. This provides novel avenues for explanation. We go on to hypothesize that the fate of the hominin in such a setting would be mutualistic coadaptation into a part-whole relation with the sociont, and we propose that the unusual suite of derived features in Homo is consistent with this hypothesis. (shrink)

Evolutionary Transitions in Individuality have been responsible for the major transitions in levels of selection and individuality in natural history, such as the origins of prokaryotic and eukaryotic cells, multicellular organisms, and eusocial insects. The integrated hierarchical organization of life thereby emerged as groups of individuals repeatedly evolved into new and more complex kinds of individuals. The Social Protocell Hypothesis proposes that the integrated hierarchical organization of human culture can also be understood as the outcome of an ETI—one that produced (...) a “cultural organism” from a substrate of socially learned traditions that were contained in growing and dividing social communities. The SPH predicts that a threshold degree of evolutionary individuality would have been achieved by 2.0–2.5 Mya, followed by an increasing degree of evolutionary individuality as the ETI unfolded. We here assess the SPH by applying a battery of criteria—developed to assess evolutionary individuality in biological units—to cultural units across the evolutionary history of Homo. We find an increasing agreement with these criteria, which buttresses the claim that an ETI occurred in the cultural realm. (shrink)

Human cooperation is highly unusual. We live in large groups composed mostly of non-relatives. Evolutionists have proposed a number of explanations for this pattern, including cultural group selection and extensions of more general processes such as reciprocity, kin selection, and multi-level selection acting on genes. Evolutionary processes are consilient; they affect several different empirical domains, such as patterns of behavior and the proximal drivers of that behavior. In this target article, we sketch the evidence from five domains that bear on (...) the explanatory adequacy of cultural group selection and competing hypotheses to explain human cooperation. Does cultural transmission constitute an inheritance system that can evolve in a Darwinian fashion? Are the norms that underpin institutions among the cultural traits so transmitted? Do we observe sufficient variation at the level of groups of considerable size for group selection to be a plausible process? Do human groups compete, and do success and failure in competition depend upon cultural variation? Do we observe adaptations for cooperation in humans that most plausibly arose by cultural group selection? If the answer to one of these questions is “no,” then we must look to other hypotheses. We present evidence, including quantitative evidence, that the answer to all of the questions is “yes” and argue that we must take the cultural group selection hypothesis seriously. If culturally transmitted systems of rules (institutions) that limit individual deviance organize cooperation in human societies, then it is not clear that any extant alternative to cultural group selection can be a complete explanation. (shrink)

We study game-theoretic models of human evolution to analyze fundamentals of human nature. Rival-claimants games represent common situations in which animals can avoid conflict over valuable resources by mutually recognizing asymmetric claiming rights. Unlike social-dilemma games, rival-claimants games have multiple equilibria which create a rational role for communication, and so they may be good models for the role of language in human evolution. Many social animals avoid conflict by dominance rankings, but intelligence and language allow mutual recognition of more complex (...) norms for determining political rank or economic ownership. Sophisticated forms of economic ownership could become more advantageous when bipedalism allowed adaptation of hands for manufacturing useful objects. Cultural norms for claiming rights could develop and persist across generations in communities where the young have an innate interest in learning from their elders about when one can appropriately claim desirable objects. Then competition across communities would favor cultures where claiming rights are earned by prosocial behavior, such as contributions to public goods. With the development of larger societies in which many local communities share a common culture, individuals would prefer to interact with strangers who identifiably share this culture, because shared cultural principles reduce risks of conflict in rival-claimants games. (shrink)