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The Evolutionary Calculus of Depression: Page 3 of 3

The Evolutionary Calculus of Depression: Page 3 of 3

None of this suggests that depression is an adaptation rather than a pathology. The “coordination” of symptoms is post facto rationalization: with sufficient imagination, one can view nearly any mental illness as an orderly and useful syndrome. Schizophrenia, for example, could be considered a cluster of “coordinated” symptoms that enable individuals to discard a reality that is simply too painful to bear. Without information that depression enhances reproduction, the idea of adaptive “coordination” is mere storytelling.

More important, there are alternative explanations for disorders that are fairly common and have some genet-ic underpinning. Take alcoholism, which has an incidence similar to that of depression (about 7%) and appears to have some genetic basis. But nobody maintains that alcoholism is adaptive. Rather, it’s almost certainly a pathological effect of an environmental change (the discovery of fermentation and distillation) on an adaptive trait (the evolved wiring and pleasure centers of our brain). Like the painful and sometimes fatal childbirth that is the by-product of selection for larger human brains, depression could simply be a maladaptive by-product of a feature that is generally adaptive—perhaps the wiring of those brains. Viewed in this way, depression could be a “spandrel,” a genetic hitchhiker that is a by-product of something else.5

Alternatively, genes that cause depression might have some advantage when they are present but do not produce the disorder. This can happen if the condition has what geneticists call “variable penetrance”: 10% of individuals carrying the dominant gene for retinoblastoma, for instance, don’t develop the disease. Or, genes that cause depression only when present in two copies could, when present in heterozygous (one-copy) conditions, have another, unknown advantage. Note that these two scenarios offer an adaptive explanation for depression genes that do not view the condition itself as adaptive. And both can be tested, for they predict that the non-depressed relatives of depressives (who carry but don’t express “depression genes”) should have higher reproductive output than do non-depressed people whose relatives are also not depressed.

This critique of the ARH applies, of course, to other adaptive explanations of depression, including the plea for help theory,6 the social rank theory,7 and the depressive realism theory.8 Some have also suggested that depression is adaptive because it and other affective disorders are associated with high creativity.9 This suggestion is also dubious because there is no evidence that depressed people who are creative have a higher reproductive output than other members of the population.

Andrews and Thomson conclude that in view of the ARH, problem-solving therapies like cognitive-behavioral therapy are the go-to treatments for depression. Further, they say, doctors should not be too hasty in prescribing antidepressant medication because the afflicted should be willing to “endure the pain”1(p645) in hopes of a more permanent, evolution-based cure. Indeed, one could read the ARH as suggesting that depression should not be cured, but cultivated!

But Andrews and Thomson’s prescriptions lose force to the extent that they rest on a flawed biological premise. Of course researchers should continue to compare talk therapies and to determine which, if any, drugs are useful in alleviating depression. But in the meantime, let’s not expropriate and distort evolutionary theory in a misguided attempt to claim mental disorders as “adaptations.”

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References

References

1. Andrews PW, Thomson JA Jr. The bright side of being blue: depression as an adaptation for analyzing complex problems. Psychol Rev. 2009;116:620-654.
2. Lehrer J. Depression’s upside. New York Times. February 25, 2010.
3. Coyne JA. Is depression an evolutionary adaptation? [Part 1] http://whyevolutionistrue.wordpress.com/2009/08/29/is-depression-an-evolutionary-adaptation-part-1. [Part 2] http://whyevolutionistrue.wordpress.com/2009/08/30/is-depression-an-evolutionary-adaptation-part-2. Accessed May 25, 2010.
4. Lonnqvist JK. Suicide. In: Gelder MN, Andreasen, Lopez-Ibor J, Geddes J, eds. New Oxford Textbook of Psychiatry. 2nd ed. Oxford, UK: Oxford University Press; 2009:951-957.
5. Pies R. The myth of depression’s upside. PsychCentral. http://psychcentral.com/blog/archives/2010/03/01/the-myth-of-depressions-upside. Accessed May 25, 2010.
6. Keedwell P. How Sadness Survived: The Evolutionary Basis of Depression. Oxford, UK: Radcliffe Publishing; 2008.
7. Gilbert P, Allan S. The role of defeat and entrapment (arrested flight) in depression: an exploration of an evolutionary view. Psychol Med. 1998;28:585-598.
8. Taylor SE. Positive Illusions: Creative Self-deception and the Healthy Mind. New York: Basic Books; 1991.
9. Andreasen NC. Creativity and mental illness: prevalence rates in writers and their first-degree relatives. Am J Psychiatry. 1987;144:1288-1292.
 
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