Considering the evolutionary benefits and costs of friendship networks

Recent efforts have sought to redress the relative paucity of theoretical work on the adaptive benefits that led friendships to be fundamentally important close human relationships (e.g., viewing investment in them as stake-based). Still, relatively little work has specifically addressed adaptations that function to developing, maintaining, and regulating friendship networks, generally consisting of multiple friends. This paper explores this domain. Following other scholars, we observe that a key quality of friendships that maintains stake-based investment in them is irreplaceability. Adding a friend to one's friendship network may have marginal net benefits. Yet the added friend may not only be less irreplaceable than others in the network; the added friend may reduce the irreplaceability of other friends in the network, thereby potentially weakening stake-based investment crucial to friendship. We discuss multiple adaptive problems that arise and potential solutions to them, suggestive of adaptations that people possess for the function of developing, maintaining, and regulating friendship networks. Future directions for potentially fruitful conceptual and empirical exploration are discussed, as are potential domains of application to understanding friendship more broadly.