In his recent ARCHIVES article, Nesse1 discusses depression as a possible evolutionary adaptation. Dr Nesse presents some interesting arguments that in certain stressful situations, the symptoms of depression can help increase the likelihood of an individual's survival. One cardinal symptom of depression that Dr Nesse fails to discuss, however, is suicidal behavior.
Feder R. Clinical Depression Is a Disease State, Not an Adaptation. Arch Gen Psychiatry. 2001;58(11):1084. doi: