The Evolutionary Basis for Human Tolerance: human 'self-domestication' (original) (raw)

Primate individuals use a variety of strategies in intergroup encounters, from aggression to tolerance; however, recent focus on the evolution of either warfare or peace has come at the cost of characterizing this variability. We identify evolutionary advantages that may incentivize tolerance toward extra-group individuals in humans and nonhuman primates, including enhanced benefits in the domains of transfer, mating , and food acquisition. We highlight the role these factors play in the flexibility of gorilla, chimpanzee, bonobo, and human behavior. Given humans have an especially broad range of intergroup behavior, we explore how the human foraging ecology, especially large spatial and temporal fluctuations in resource availability, may have selected for a greater reliance on tolerant between-community relationships-relationships reinforced by status acquisition and cultural institutions. We conclude by urging careful, theoretically motivated study of behavioral flexibility in intergroup encounters in humans and the nonhuman great apes. K E Y W O R D S cooperation, hominoids, human evolution, intergroup encounter, primate behavior, sociality, tolerance 1 | INTRODUCTION Attempting to explain the prevalence of intergroup aggression in primates , especially in humans (Homo sapiens sapiens), evolutionary anthropologists have focused extensively on intergroup contest and warfare. In response, other evolutionary anthropologists have focused extensively on peace systems in primates, especially in humans. Focus-ing on these two ends of the spectrum-war or peacefulness-has come at the cost of fully characterizing within-species variation in individuals' behavioral strategies in intergroup encounters (e.g., Refs. 1-4; see also, Ref. 5: table 22-1). Furthermore, both of these approaches emphasize selection pressures that favor or disfavor intergroup aggression; less researched are the selection pressures that, given disincentives for intergroup aggression, favor tolerant encounters and the prolongment of tolerant encounters in intergroup association. In the present review, our goal is to call for explicit theorization about the individual-level selection pressures that favored flexible behavior in intergroup encounters in humans and nonhuman primates, especially the often-overlooked pressures that may favor tolerant encounters and association given disincentives for aggression. We review how tolerant behavior toward extra-group conspecifics in specific domains-such as food access, mating, and reconnaissance before transfer-may have been favored by natural selection in nonhuman primates. In the course of this review, we pay special attention to the group-living, nonhuman great apes, but not because these species are necessarily the best analogies for intergroup behavior in humans. We focus on these species for two reasons: first, due to our common ancestry, humans and the extant non-human great apes share a number of traits derived within the Primate order, suggesting that there is (at least some) insight to be gained by drawing comparisons between these species; and second, to highlight