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The discipline of evolutionary psychology views modern human behaviors as products of natural selection that acted on the psychological traits of our ancestors. A subdiscipline, evolutionary psychiatry, tries to find evolutionary explanations for mental disorders.
One of the most common subjects of evolutionary psychiatry is depression. Although debilitating, depression is also reasonably widespread. Estimates of its prevalence in Western nations range between 5% and 20%, and the disorder appears to depend at least partly on an individual's genes. The relatively high frequency of an apparently maladaptive and partially genetic syndrome has led to speculation that it may really be "adaptive" in an evolutionary sense-that is, a liability to depression may have been installed in our genome by natural selection.
A recent version of this idea is the adaptive rumination hypothesis (ARH) of Andrews and Thomson,1 which posits that depression evolved as a way to solve difficult and complex problems, most of them involving social interactions. Instead of being a pathology, depression is seen as a useful complex of thoughts and behaviors that enable troubled people to withdraw from the world, deliberate intensively about their social problems, and devise solutions. Andrews and Thomson suggest this behavior evolved because it was adaptive in our ancestors, and may still be so.
The ARH has attracted a good deal of attention, much of it favorable. It was, for example, the subject of a recent article in The New York Times magazine.2 Debate about the ARH is not purely academic, for Andrews and Thomson see the idea as pointing to specific therapies, including problemsolving talk therapies and the deliberate withholding of medication. Since these suggestions stem from a specific evolutionary hypothesis, we should carefully examine that hypothesis.
I have previously discussed a number of troubling problems with the ARH.3 Andrews and Thomson deliberately conflate clinical depression and simple sadness, assuming that these are simply positions on a continuous psychological gradient. They give no evidence that depression is caused by, rather than the cause of, difficult social problems, and they fail to show that depression actually helps people solve those problems. And many of the "experiments" supporting the ARH are unrealistic, bordering on silly. One such study mimicked the effect of depression on problem solving by having people engage in...