Can the parochial cooperation hypothesis explain the evolution of human cooperation? Quantifying cooperative investments in an agent-based model

Abstract

The parochial cooperation hypothesis posits that violent conflict between ancestral groups played a key role in the evolution of human cooperation. To date, this controversial idea has been supported by several computational models illustrating potential mechanisms through which costly cooperation could be sustained by intergroup conflict. However, it remains unclear whether the cooperative costs these models impose constitute meaningful fitness investments; therefore, it could be that the evolutionary dynamics being described are inconsequential in the context of human evolution. Here, we take the most famous of these models and demonstrate that if analysed with this consideration in mind, the model’s support for the parochial cooperation hypothesis becomes tenuous. Specifically, we show that this model can only sustain trivial levels of cooperative investment under most conditions, suggesting that intergroup conflict did not impose meaningful selection for cooperation throughout human evolution. While these findings challenge the theoretical underpinnings of the parochial cooperation hypothesis, our method for quantifying cooperative investments offers avenues to better test these kinds of ideas moving forward.