Strong ties promote the evolution of cooperation in dynamic networks

•Tie strength impacts the evolution of cooperation in dynamic networks.•We use mixed methods to test our arguments and find support.•Experimental and agent-based simulations support the logic of our argument.•We illustrate how a relational and inherently social factor contributes to the evolution of cooperation.

Research on the evolution of cooperation in networked populations has assumed that ties are simply present or absent. Here we bring relational sociological insights about the strength of ties to bear on the problem of cooperation in dynamic networks. We argue that the value of ties affects their strength, which in turn promotes cooperation. We evaluate this argument with two studies. First, results from an agent-based model are consistent with the logic of our argument and are robust across a variety of initial conditions. Second, results from a controlled laboratory experiment with human participants support the key predictions. Across both studies we demonstrate that tie strength, operationalized as relationship duration, mediates the impact of tie value on cooperation.