Endocrine response and social behaviour: relationships between steroid hormones and prosocial cooperation in Prisoner's Dilemmas

Individuals of social species are faced with the problem of deciding which group members and circumstances warrant social cooperation when selfishness often leads to greater rewards. The cognitive processes used to resolve this problem have been shaped, alongside biological systems, by evolution. The hormones testosterone (T) and cortisol (C) are involved in aspects of social relationships and cognition, and are therefore potential modulators of these cooperative strategies. Two experiments were conducted to explore the relationship between these hormones and social cooperation, using the Prisoner's Dilemma and Public Goods Game to account for pair and group cooperation respectively. Salivary T and C concentrations were compared with game performance against predetermined opponent strategies, which ranged from very to not at all cooperative. Results did not confirm a relationship between baseline levels of T or C and social cooperation, nor did opponent strategy influence participants' T or C.