Diverse and Flexible Strategies Enable Successful Cooperation in Marmoset Dyads.

In humans, cooperation relies on advanced social cognition, but the extent to which these mechanisms support cooperation in nonhuman primates remains unclear. To investigate this, we examined freely moving marmoset dyads in a cooperative lever-pulling task. Marmosets successfully coordinated actions, relying on social vision rather than environmental cues. Blocking visual access or replacing the partner with an automated agent disrupted coordination. Causal dependencies between social gaze and pull actions revealed both gaze-dependent and gaze-independent strategies. Cooperation depended on social relationships, including dominance, kinship, and sex. Remarkably, marmosets adapted strategies based on partner identity, indicating rapid social learning and memory. Altogether, these findings show that flexible, cognitively driven cooperation extends more broadly across primates than previously recognized, informing our understanding of cooperative behavior's mechanisms and evolution.