The purpose of depression

Paul Andrews, an evolutionary psychologist at McMaster University in Canada argues that depression may be “an adaptation for analyzing complex problems.” He sees it in the condition’s bouquet of symptoms, which include “anhedonia,” or an inability to feel much pleasure; people who are depressed ruminate frequently, often in spirals; and they get more REM sleep, a phase associated with memory consolidation. This reflects an evolutionary design, the argument goes, one that’s to, as Hutson summarizes, “pull us away from the normal pursuits of life and focus us on understanding or solving the one underlying problem that triggered the depressive episode.” Like, say, a “failed” relationship. The episode, then, is a sort of altered state, one different from the hum of daily life, one that’s supposed to get you to pay attention to whatever wounding led to the upset. For example, 80 percent of subjects in a 61-person study of depression found that they perceived some benefit from rumination, mostly assessing problems and preventing future mistakes.

If interested read more:

http://nymag.com/scienceofus/2017/02/a-new-way-to-understand-and-treat-depression.html