Cooperation is essential for group survival and success. Inequality among group members can undermine voluntary cooperation in groups, and this problem is exacerbated when those with less power observe those with more power behave selfishly. We propose, and empiricaly demonstrate, that even when powerholders behave selfishly and messages are nonbinding and unverifiable, communication with group members fosters cooperation in hierarchical groups. We introduce a novel experimental task to study how communication influences cooperation in groups. In the ABC game, three individuals take turns choosing whether to Add resources to a collective pool (A), Claim resources from that pool (C), or do Both simultaneously (B), thereby gaining less but without depleting the pool. In our study, powerholders made the first choice in each block of decisions and had unlimited power to allocate resources after the task. They were both first movers and final decision makers. We constrained powerholders' behavior to be selfish or cooperative by restricting their choice set: some powerholders had only choices A and B available to them, whereas other poweholders had only choices C and B available to them. In addition, half the groups could communicate, whereas the other half could not. Our findings (N = 3690 incentivized decisions) demonstrate that nonbinding communication significantly increases cooperation in hierarchical groups even when powerful group members are constrained to behave selfishly, challenging the notion that actions always speak louder than words.
