Dr Nesse, in raising the question, "Is Depression an Adaptation?"1 has contributed greatly to understanding this poorly understood, unpredictable condition. He offers many possible functions for low mood and depression, but he stops short of firmly concluding that depression has adaptive significance.
A strong case for the phylogenetically adaptive significance of depressive symptoms can be made, however. Depression has a genetic component: parents of persons with major depressive disorder (MDD) are 2 to 3 times more likely to have had the disease themselves than parents of persons without depression.2 Depression is also common. Lifetime prevalence of MDD is 15.8%.2 The rate of spontaneous mutation in humans is 1 per 10 000 to 1 per 1000.3 Taking the conservative values of 1 in 10 for MDD and a mutation rate of 1 per 1000, depression is observed at more than 100 times the mutation rate. Depression must have had a definite selective advantage in the ancestors of modern humans; otherwise, it would be rare.
Longley AJ. Depression Is an Adaptation. Arch Gen Psychiatry. 2001;58(11):1083. doi:
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