Collective narratives catalyse cooperation

Humans invest in fantastic stories -- mythologies.Recent evolutionary theories suggest that cultural selection may favour moralising stories that motivate prosocial behaviours.A key challenge is to explain the emergence of mythologies that lack explicit moral exemplars or directives. Here, we resolve this puzzle with an evolutionary model in which arbitrary mythologies transform a collection of egoistic individuals into a cooperative. Importantly, in finite populations, reflecting relative to contemporary population sizes of hunter-gatherers, the model is robust to the cognitive costs in adopting fictions. This approach resolves a fundamental problem across the human sciences by explaining the evolution of otherwise puzzling amoral, nonsensical, and fictional narratives as exquisitely functional coordination devices.