We've all heard the idea that depression involves a chemical imbalance in the brain. Perhaps it comes from a deficiency in the neurotransmitter serotonin. We've also been told that antidepressants work by reversing this deficiency.

For example, Medline, an informational website hosted by the National Institutes of Mental Health, tells us that the drug imipramine works by “increasing the amounts of certain natural substances in the brain that are needed to maintain mental balance.”

If that's true, depressed people ought to take antidepressants in the same way that diabetics ought to take insulin. What could be more natural than to take a drug that reverses a disorder?

Yet recent research has shown that there's almost no evidence that depression stems from a serotonin deficiency. Some studies even suggest that, except in the most severe cases, antidepressants scarcely outperform placebos. Perhaps it's time for a different approach.

On a newer view associated with the school of thought known as evolutionary psychiatry, depression isn't usually a “disorder” or “disease” at all. It's a healing mechanism in its own right.

Consider fever. Before the 1700s, doctors thought fever – the heat associated with infection –........

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