On the interplay of hierarchies, conflicts, and cooperation: An experimental approach

Abstract

Previous research suggests that it is difficult to maintain cooperation in a large society when there is a strong hierarchical structure. In this study, we implement online human experiments to study the effects of exogenous variation in a particular notion of hierarchy on cooperation and conflict within groups. We demonstrate how cooperation can be maintained when collective action is accompanied by dyadic conflicts whose outcome feeds back on the hierarchical rank of the contestants. We find that the majority of individuals take part in conflicts and that highly ranked individuals mostly cooperate and engage in conflicts as a way to punish noncooperators. As a consequence, stable hierarchical groups can arise and maintain high levels of cooperation. Our results are in agreement with the prediction of earlier theoretical models on hierarchical societies and are relevant to understanding the interplay of hierarchy, cooperation, and conflict.

Keywords: behavioral economics; cooperation; hierarchies; online experiments.

Fig. 1.

Experimental setup. In each treatment, participants went through 60 rounds including two phases. In the first phase, they take part in a PGG with a multiplication factor set to be half of the group size. In the second phase, they could engage into conflict against their coupled participant to steal from them their round earnings. In the egalitarian group treatment, ranks were not present and conflicts were randomly decided with 50% probability of winning for both participants. In the Hierarchical (small hierarchy and large hierarchy) treatments, ranks changed after each engaged conflict and winning probabilities were rank-dependent. See the main text and the Supplementary Information (SI) Appendix for more details on the experiment.

Fig. 2.

Cooperation frequency and rank changes by round and treatment. (a) Observed cooperation levels are higher and more stable with respect to previous PGG that did not include conflicts and/or hierarchical structures. (b) The larger the number of rank changes is, the less the established hierarchy can be considered as stable. As the number of rank changes decreases with time, we find that hierarchies are more stable in larger groups than in smaller ones. Error bars represent the Standard Error of the Mean (SEM) considering each group as an independent observation.

Fig. 3.

Participants’ conflict frequency distribution by treatment. Participants are involved in a conflict more often in hierarchical treatments with respect to the egalitarian group treatment. Furthermore, conflict frequencies follow normal distributions for both hierarchical treatments.

Fig. 4.

Attack frequency by treatment and contribution decisions. Participants who contributed in the first phase, i.e., cooperators, are more willing to engage into a conflict against defectors, i.e., not contributors, especially in the egalitarian group treatment. Defectors, instead, do not discriminate between defectors and cooperators in the egalitarian group treatment, while they do in hierarchical treatments.

Fig. 5.

Cooperation and attack frequencies by rank position and treatment. Highly ranked participants cooperate and engage into conflicts more often than lowly ranked ones for both hierarchical treatments. Both frequencies follow linear fits. For comparison purposes with large hierarchy treatment results, we report dashed lines for the small hierarchy treatment as projected frequencies for ranks that are not reachable in small groups. Cooperation and attack frequencies of the egalitarian group treatment are reported as the average value observed in the entire treatment. Error bars represent the SEM considering each individual decision as an independent observation.