Cooperation investments: Building capacity and signaling intent

People do not just cooperate — they regularly invest in their cooperative abilities. Partners learn to resolve conflicts, colleagues train for their roles within large teams, and people adopt the shared practices of their community. Often, these activities do not benefit others per se. Rather they facilitate future cooperative interactions. Yet such cooperation investments are rarely captured in evolutionary game theory, which focuses on cooperative decisions instead of the preparatory efforts that enable them. Here, we develop a model that allows individuals to incur upfront costs to lower their future cooperation costs. Through mathematical analysis and evolutionary simulations, we show that cooperation investments serve a dual function. First, they allow individuals to transform into more effective partners, enabling cooperation where it would otherwise be too costly. Second, they can serve as honest signals of cooperative intent. When their costs deter would-be cheaters, investments allow observers to identify trustworthy partners, further expanding the cooperative domain. Our model helps to explain why people are attentive to others’ cooperation investments. When someone takes the time to learn more about a partner's hobbies or a community's norms, they do more than build capacity — they signal an intent to cooperate with us.