Social role specialization promotes cooperation between parents

Biparental care of offspring is a widespread social behavior, and various ecological, life-history and demographic factors have been proposed to explain its evolution and maintenance. Raising offspring generally requires several types of care (e.g. feeding, brooding, defense), and males and females often specialize in providing different types of care. However, theoretical models of care often assume that 'care' is a single variable, and hence that a unit of care by the mother is interchangeable with a unit of care by the father. We hypothesize that the ability of one parent to provide all types of care may be limited by non-additive costs, or by sex-based asymmetries in the costs of particular care types. Using an individual-based simulation, we show that synergistic costs of investing in two tasks, or a negligible sex-based cost asymmetry, select for task specialization and biparental care. Biparental care persists despite intense sexual selection and sex-biased mortality, suggesting ...