Bargaining models of depression and evolution of cooperation

This paper presents a model for evolutionary origins of unipolar depressive disorders and reviews empirical evidence in support of the "nonparticipation hypothesis of depression" suggested by the model. In line with previous theory, depression is interpreted to provide means for not participating in joint enterprises that would otherwise be difficult to avoid ('bargaining' model); therefore, it provides an additional alternative strategy to social-imitation dynamics occurring in Public Good Games. Average income from joint enterprises modeled with a Public Good Game is interpreted to drive group-level genetic selection. Based on these assumptions, it is shown that if a joint enterprise is sufficiently important for both the between-individual and the between-groups competition, then a nonparticipation strategy (or gene for depression vulnerability) will be present in total population almost surely (i.e., with probability one). The modeling framework serves to explain several other seemingly unrelated empirical observations, such as association between income inequality and depression, co-morbidity and proximal biological mechanisms for negative emotions, and mechanisms for the social network-dynamics of emotion.