Intergroup Conflict Drives Commitment Signalling: A Cross-Cultural Experimental Evidence

Human evolutionary history has been shaped by recurrent intergroup conflict, in which cooperation with group members carries high stakes and defection entails severe consequences. Such pressures should trigger evolution of mechanisms reliably communicating group commitment. Here, we test whether sacrificing strategic resources to signal group commitment may have evolved as such a mechanism. Using a public goods game with a cross-cultural sample (N = 2,745 participants from eight countries), we manipulated intergroup conflict by allowing some groups to compete over collective resources and permitting individuals to defect to the opposing group. Participants could signal cooperative commitment by sacrificing a portion of their endowment. We find that intergroup conflict (compared to no conflict condition) increases signalling both when signalling is costly and when it is relatively symbolic, suggesting that in conflict contexts, individuals exploit any available signalling opportunity, regardless of cost. Sensitivity to intergroup conflict in signalling behaviour was stronger in countries with higher recent exposure to intergroup violence. Moreover, individuals who signalled contributed more to the public good despite reduced endowments and were less likely to defect. Simulations of 10,000 conflicts showed that signalling groups were almost four times more likely to win a conflict than non-signalling groups. These findings indicate that intergroup conflict may have been a key selective pressure in the evolution of commitment signalling, with implications for how past and present societies build trust, sustain cooperation, and deter defection in competitive settings.