Depression as Adaptation

There is an interesting new evolutionary psychology book from Paul Keedwell named How Sadness Survived: The Evolutionary Basis of Depression, published by Radcliffe Publishing, 2008. Why should a condition causing so much distress and disability as depression occur so commonly? The thesis of the book is that depression has evolved to avoid the pursuit of unachievable goals. Pursuit of unachievable goals leads obviously to perpetual goal frustration. Giving up unrealistic dreams can often bring the dark feelings of depression to an end. Therefore depression may be a mechanism which has evolved to give up unachievable and unrealistic goals, to withdraw from futile activities, and to conserve energy. It is a mechanism that encourages people to make changes in their life, and to find new goals: by marking all existing goals as unbearable and pointless. Depression can be considered as adaptive in situations where continued effort to pursue a certain goal will result in either danger or loss of valuable resources. In other words, depression is an adaptation to desperate and hopeless situations (i.e. to situations and environments where continued effort to pursue a certain goal will result in either danger or loss of valuable resources.)

And it is useful to request help from others. Keedwell says: “social support and interdependence were important features of the [human] ancestral environment […] the group could have offered extra help to the depressed person until the condition resolved. […] a depressed person may change the attitudes of other people around him, making them more sympathetic to his needs and therefore giving him a long term [social or reproductive] advantage.”

Stress biases decision-making strategies. It makes sense that short-term stress leads to more of the same actions (very strong stress will result in the binary flight or fight action response), while chronic long-term stress leads to less of the same, because it is time to try something new. Basically depression is the demand of the body to try something new, to find new goals, to do less of the actions which led to the current unpleasant situation. As if the body is saying “do anything, but don’t do this anymore”.

P.S. Recent studies have found that depression in form of prolonged stress exposure causes architectural changes in prefrontal dendrites. Chronic stress is known to damage, degenerate and shrink the hippocampus, and it impairs prefrontal cortex-sensitive working memory. A mechanism which degenerates the PFC will help to give up unrealistic dreams and unachievable goals.

Update (14 Mar. 2010) : P.S. Recent articles in the NYTimes and the Economist (named Depression’s Upside and The evolutionary origin of depression) support and confirm the idea that depression is probably linked to how willing someone is to give up his goals. Pain and low mood are warning mechanisms. Both are a natural part in dealing with failure. It is healthy for an organism to experience a decline in motivation if a goal is unreachable or dangerous. Pain stops you doing pursuing goals that damage the physical integrity of the body. Low moods and depression stop you pursuing overly ambitious or unreachable goals in general. In this sense, depression is a natural “give up” mechanism that protects an organism.