Positive Side to Depression

Evolutionary biologists have been trying to find a link between depression and increased ability to problem solve. Their studies have shown that when subjects are presented with a spatial pattern test they get sad and are then able to solve it faster. Other studies have shown that sad or depressed people are better judges of deception. However, other psychologists and psychiatrists say that these tests have not been done with actual depressives so they may not show an evolutionary need for depression.
http://www.nytimes.com/2012/01/17/health/depression-defies-rush-to-find-evolutionary-upside.html?ref=biologyandbiochemistry