Punishment sustains large-scale cooperation in prestate warfare

Abstract

Understanding cooperation and punishment in small-scale societies is crucial for explaining the origins of human cooperation. We studied warfare among the Turkana, a politically uncentralized, egalitarian, nomadic pastoral society in East Africa. Based on a representative sample of 88 recent raids, we show that the Turkana sustain costly cooperation in combat at a remarkably large scale, at least in part, through punishment of free-riders. Raiding parties comprised several hundred warriors and participants are not kin or day-to-day interactants. Warriors incur substantial risk of death and produce collective benefits. Cowardice and desertions occur, and are punished by community-imposed sanctions, including collective corporal punishment and fines. Furthermore, Turkana norms governing warfare benefit the ethnolinguistic group, a population of a half-million people, at the expense of smaller social groupings. These results challenge current views that punishment is unimportant in small-scale societies and that human cooperation evolved in small groups of kin and familiar individuals. Instead, these results suggest that cooperation at the larger scale of ethnolinguistic units enforced by third-party sanctions could have a deep evolutionary history in the human species.ver the last 50,000 y, humans have come to dominate the world's biota, in part because we cooperate on larger scales than other mammals. Recent models suggest that informal systems of punishment can maintain cooperation in large groups (1, 2). However, this work leaves two important questions unanswered. First, does punishment actually play an important role in sustaining human cooperation in the absence of formal coercive institutions? In laboratory experiments third parties-individuals who are not the primary party injured by a defection-bear costs to punish defectors (3, 4). However, scholars have questioned whether such punishment exists outside of laboratory settings (5) and, even if punishment does occur, whether it effectively promotes cooperation (6)(7)(8). Second, what is the scale of human cooperation? Punishment can sustain cooperation on scales ranging from small kin-based hunter-gatherer bands to large modern states (9). A common view is that the psychology that sustains human cooperation evolved in small foraging bands characterized by modest levels of genetic relatedness and repeated social interactions (10, 11), and this led to a psychology that supports bandlevel cooperation. According to this view, large-scale cooperation occurs only when this psychology "misfires" in novel modern social environments with coercive institutions. An alternate view is that humans have evolved to cooperate in ethnolinguistic groups (groups with shared cultural norms and language), comprising thousands of unrelated strangers, even without formal coercive institutions (12, 13). According to this view, the scale of human cooperation has been shaped by competition between culturally distinct groups, which led to sanctioning systems that enforce cooperation ...

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The evolution of altruistic social preferences in human groups

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