ABSTRACT
Cooperation determines the success or failure of human interactions ranging from everyday social exchange, to global trade, environmental management, and international conflict. Yet, strangely enough, this fundamental aspect of human behavior remains poorly understood and a topic of great debate spanning several disciplines. Since the mid-1960s, cooperation was widely understood as promoting the inclusive fitness of the individual cooperator. However, in the past few years, researchers have asserted that the unprecedented extent of cooperation among human groups of nonkin (e.g., in collective actions) lies beyond the explanatory power of individual-level theories. These researchers argue that this unusual level of cooperation demands a special, higher level explanation such as
biological or cultural group selection. While humans are indeed unusually cooperative, we outline evidence suggesting that cooperation is best explained not in terms of group-level adaptation, but rather by applying, extending, and synthesizing existing theories of individual-level adaptation. Specifically, we contend that (1) most humans are “conditional reciprocators,” who cooperate to whatever extent their interaction partners do (a Triversian reciprocity model) and (2) cooperators can achieve “positive assortment” and, thus, outcompete free riders, by preferentially interacting with other cooperators (a Hamiltonian positive assortment model). Previous models have tended to examine Triversian and Hamiltonian processes in isolation, yet the synergistic effects between them may account for the evolution and maintenance of collective action. In this chapter, we present (1) an overview of evolutionary accounts of human cooperation and how they have changed over time, (2) a theoretical model demonstrating how a strategy for continuous (as opposed to binary) reciprocity in sizable groups could replicate successfully in a population of competing strategies, and (3) empirical evidence from several different disciplines which suggests that most people do in fact act as positively assorting reciprocators in group interactions. Group selection is possible in theory but remains unnecessary to explain the diversity and prevalence of human cooperation. As we argue, the current focus on group selection stems from an erroneous fork along the road of research on human cooperation, traceable to a specific influential model of reciprocity by Robert Boyd and Pete Richerson in 1988. Our initial exploration of the alternative path suggests there are fruitful avenues for a much improved understanding of human cooperation.
