History

• Darwin observed in 1876 that suffering was compatible with the theory of natural selection, since natural selection is not perfect, but only provides for competition of species. According to Darwin, creatures can be guided to beneficial action by suffering, by pleasure, or by both in combination, and natural selection has caused most creatures to be guided by pleasurable sensations, which can be continued without giving rise to depression.
  
  

Social Benefits

• Many recent theories about the evolutionary function of depression stress the social advantages that depression confers. Leon Sloman of the University of Toronto and Clarke Institute of Psychiatry argued in a 1992 article in "Psycoloquy" that variations in mood help to regulate the aggressive behaviors necessary for survival. In this theory, feelings of inadequacy, discouragement and hopelessness turn off aggression, which allows the person who is losing the conflict to end it by submitting and elicit sympathy instead. Another possibility is that low moods due to failure help to discourage the person from that activity and instead direct his energy toward tasks to which he's better suited, allowing him to find his appropriate place in the social hierarchy.
  
  

Other Benefits

• Depressive thought tends to be both persistent and analytical, dwelling insistently on the person's problems and breaking complex problems down into parts, write Paul W. Andrews and J. Anderson Thomson Jr. in an August 25, 2009 article in Scientific American. This style of thinking helps with problem-solving, even with math problems. The desire for isolation and lack of pleasure in many activities that are part of depression also help the depressed person focus on solving her problems. Depression may be nature's way of telling the individual that she has complex social problems that her mind is working to solve, according to the authors.
  
  

Considerations

• Not all aspects or types of depression are advantageous, of course. Randolph Nesse of the University of Michigan's Department of Psychiatry argued, for example, that although depressive and anxiety disorders are extreme versions of normal evolutionary defenses such as sadness and fear, excessive expression of low mood that is prolonged or happens in the wrong situation causes pathological depression, according to a summary by the Evolutionary Psychiatry website. Suicide, in particular, poses an evolutionary paradox.
  
  

Solution

• Depression may be part of the baggage of the complex emotional lives of animals with big brains, suggests Meredith F. Small in a May 9, 2008 article for the Live Science website. The same capacity to feel that helps human beings solve problems and survive may also produce inconsolable depression of the kind that leads to suicide. On the other hand, attempted suicide may serve an adaptive function as a signal for help that allows loved ones to intervene.