Darwinian depression.

BACKGROUND

The standard evolutionary explanation for depression is that being in an emotionally depressed state is adaptive.

METHOD: The article first undertakes a critical review of the extant literature. It then provides an alternative evolutionary explanation for event-based depression and elation. It argues that being in a depressed state is not adaptive (indeed, quite the opposite), but that the threat of depression for bad outcomes and the promise of pleasure for good outcomes are adaptive because they motivate the individual toward undertaking effort that increases fitness. The article then explains reasons for failure in the motivation system and the mood disorders that arise as a consequence.

RESULTS

The article explains why motivation depends on both elation and depression and why individual happiness is not permanently improved by winning the lottery (or permanently reduced by becoming wheelchair bound). It explains the comorbidity of bipolar disorder and panic disorder, why mood stabilizers tend to reduce motivation, and when anti-depressants are unlikely to cure "laziness."

LIMITATIONS: The evolutionary explanation for depression does not directly provide clinical criteria for determining when major depressive disorder is present nor has it yet provided new treatment strategies for mood disorders.

CONCLUSIONS

The theory presented here provides a coherent explanation for depression and elation and leads research in a different direction from previous evolutionary explanations.