In the early stages of human societal development, communities were primarily close-knit, where every word and action of an individual spread among neighbors, creating tightly connected small communities. In these settings, interactions among individuals were not accidental but characterized by long-term continuity. Everyone consistently acted in ways that would shape their image and reputation within the community. This continuous interaction, resembling an expansive network, tightly interwove each individual’s fate with the others'. Against this backdrop, cooperation and mutual assistance emerged as crucial cornerstones in the early development of human societies.

This perspective is rooted in the theory of the evolution of cooperation through repeated interactions, which posits that acts of cooperation are based on the anticipation of future cooperative opportunities. Such long-term social engagements foster cooperation among individuals. However, this seemingly plausible explanation overlooks a critical detail: even within long-term interactions, individuals may engage in ambiguous reciprocal behaviors (i.e., the fuzzy reciprocation strategy), potentially undermining the foundation of cooperation. In other words, the mere expectation of future interactions does not ensure the stability of cooperation.

Another hypothesis, group competition, suggests that competition among groups fosters the evolution of cooperation. Yet, this theory also has its limitations. While inter-group competition can encourage internal cooperation, its effectiveness wanes when groups become exceedingly similar. Furthermore, even with discernible differences between groups, group competition may not efficiently bolster cooperation since cooperative groups tend to compete with each other rather than with non-cooperative groups.

A recent article in Nature addresses the limitations of these theories, illustrating that their integration can produce a synergistic effect. While the basis for cooperation in repeated interactions is fragile, group competition can mitigate the negative impact of ambiguous reciprocation strategies. Indeed, evolutionary strategies often involve cooperative behaviors towards in-group members and non-cooperative behaviors towards out-group members.

▷ Paper: Efferson, Charles, et al. "Super-additive cooperation." Nature (2024): 1-8.

The experiment was conducted in West Papua, New Guinea, where the research team selected two local communities, the Ngenika and the Perepka, to participate in a two-person sequential social dilemma game. Unlike the traditional prisoner's dilemma game, this experiment's game allowed for cooperative actions to vary continuously within a certain range, more accurately reflecting the social dilemmas humans encounter in the real world.

In this game, each participant received a certain amount of "resources." The game unfolded in two steps: initially, the first mover could choose to transfer some of their resources to the second mover, which would double during the transfer; then, based on the initial transfer, the second mover could choose to transfer some of their resources back to the first mover, which would also double. This setup not only presented an opportunity for cooperation but also posed a strategic challenge.

The experiment explored three scenarios: one featuring only repeated interaction, one with only group competition, and one that combined both. Additionally, the study examined variations in strategic space dimensions to simulate potential cooperative strategies.

The results revealed that participants engaged in higher initial resource transfers (indicating more cooperative behavior) when paired with in-group members, and lower initial resource transfers (indicating less cooperative behavior) when paired with out-group members. Importantly, the response strategies of the second movers varied significantly: responses to in-group members often increased cooperation (by augmenting resource transfers to reward the first mover’s cooperation), while responses to out-group members generally reduced cooperation (by decreasing resource transfers in reaction to the first mover’s level of cooperation).

This pattern aligned perfectly with the research team’s model predictions, suggesting that the combination of repeated interaction and group competition could create a powerful synergistic effect, fostering in-group cooperation and mitigating the negative impact of ambiguous reciprocity on cooperation.

This experiment challenges the notion that a single mechanism, such as repeated interactions or group competition alone, can account for human cooperation. It introduces a new perspective: human cooperation may have evolved under the combined influences of repeated interaction and group competition. The findings demonstrate that even in one-off interactions, cooperative behaviors are shaped by the historical legacy effects of these two mechanisms, implying that the cooperative behaviors we observe today may be a direct result of social motivations that evolved in the distant past through in-group repeated interactions and inter-group competition.

From the Ngenika to the Perepka, from forests to cities, and from ancient tribes to modern societies, the essence of cooperation has consistently permeated human interaction. This experiment serves as a mirror, reflecting the intricate and nuanced evolutionary backdrop of human cooperative behavior. The essence of human cooperation is not a product of simple algorithms but is cultivated through the complexities of repeated interactions and honed in the crucible of group competition.