Quality, quantity, and the adaptive function of social relationships

Affiliative social relationships have clear links to fitness in a variety of species, yet exactly why that is the case remains elusive. One major development has been the recognition that animals form different kinds of social relationships. These likely represent distinct evolutionary strategies, beneficial in different environments. To set the stage for investigating this idea systematically, we unify theory from socio-ecology and network science to set forth testable predictions for how social and ecological pressures drive adaptive variation in the quality and quantity of social relationships. As the number of study populations generating data on social fitness gradients is continuing to grow, this framework lays the foundation for systematic research into the adaptive function of social relationships.