Given that the principal cause of major unipolar depression is a significant negative life event, and that its characteristic symptom is a loss of interest in virtually all activities, it is possible that this syndrome functions somewhat like a labor strike. When powerful others are benefiting from an individual’s efforts, but the individual herself is not benefiting, she can, by reducing her productivity, put her value to them at risk to compel their consent and assistance in renegotiating the social contract so that it will yield net fitness benefits for her. In partial support of this hypothesis, depression is associated with the receipt of considerable social benefits despite the negative reaction it causes in others. [abstract]
Fascinating idea. Of course depression doesn't have to be voluntary or conscious for it to perform this function. So is there evidence that the desired effects are achieved by the individual exhibiting depressed behavior?
A number of behavioral studies have demonstrated that although depression in one family member prompts negative feelings from other family members, it nonetheless appears to deter their aggressive behavior and to cause an increase in their tendency to offer solutions to problems in a positive or neutral tone and an increase in their solicitous behavior (e.g., caring statements), consistent with the bargaining model. [...] Behavioral studies thus confirm that depression causes an increase in provisioning of social benefits and a decrease in aggressive responses, as predicted.
Similarly, the spouses of individuals experiencing PPD should report increasing their investment in parenting, and in fact they do. Depression scores for one spouse were positively correlated with reports of increasing investment in childcare by the other spouse (Hagen 2002). High levels of help from spouses and better interactions with infants in one study were also the only variables associated with remission of PPD (Campbell et al. 1992). [pp. 109-110]