Observational evidence that economic reciprocity pervades self-organized food co-operatives.

Evolutionary scientists argue that prosociality has been central to human ecological success. Theoretical models and behavioural experiments have found that prosociality, and cooperation in particular, is conditional and context dependent, that individuals vary in their propensity to cooperate, and that reciprocity stabilizes these behaviours within groups. Experimental findings have had limited validation with observations of behaviour in natural settings, especially in organizational contexts. Here, we report measurements of collective action, which show that reciprocity is abundant in organizations embedded in a cash economy. We study small 'food clubs', where members share bulk purchases and are considered to be heavily dependent on cooperation. We use high-resolution data on the economic interactions of 1,528 individuals across 35 clubs and over a combined 107 years of operation. We develop a network method to detect different directional and temporal forms of economic reciprocity, and statistically classify individual behavioural types akin to those in experiments. We find abundant direct reciprocity, supplemented by indirect reciprocity, and that members of most clubs can be identified as consistent reciprocators. This study provides initial observational evidence that economic reciprocity may be more abundant in real-world settings, sharpening the findings of the behavioural study of cooperation and contributing to the more naturalistic study of reciprocity and prosociality.