an Adaptation for Overcoming Constraints of the Social Niche:

We outline a new theoretical model of the evolutionary adaptiveness of minor and major unipolar depression. According to our social navigation / social niche change model, the evolved function of depression is the analysis and eradication of a severe socially imposed mismatch between the depressive’s capacities and opportunities for fitness-enhancing activity, where the constraints responsible for the mismatch have a broad or even pervasive basis in the individual’s social network. Minor depression, which we operationally define as a level of depression that can be intentionally hidden from social partners (and often is), optimizes the mind in several ways for (1) identifying possible mismatch-reducing revisions of the individual’s socioeconomic niche and (2) planning active negotiating tactics to achieve their implementation. Major depression may ensue in cases where active tactics of negotiation or coercion consistently fail to yield the investments and concessions from social partners required for substantive niche revision. Watson, PJ & Andrews, PW. 2002.

Toward a revised evolutionary adaptationist analysis of depression:

The social navigation hypothesis. JAD 72, 1-14