For anyone who has been depressed, it is difficult to conceive of depression as something ever useful. Depression immobilizes people, and the core symptom is anhedonia, the inability to feel pleasure. From the perspective of depressed people, these add up to a living hell. The World Health Organization estimates that depression is the fourth leading cause of disability in the world, and that it is projected to become the second leading cause of disability. I recently finished watching a “Great Courses” video lecture series called “Stress and Your Body,” featuring Robert Sapolsky, who described the strong correlation between stress and depression. He indicated that lack of outlets, lack of social support and the perception that things are worsening are precursors to depression.
In an article titled “Is Depression an Adaptation?” psychiatrist Randolf Nesse terms depression “one of humanity’s most serious medial problems.” Nesse also argues, however, that many instances of depression are actually adaptive. How could this possibly be? Nesse explains:
It is easy to see how lack of motivation for one activity could free effort for something more productive, but depression is characterized by a more pervasive pessimism, low self-esteem, and reduced initiative. These characteristics pose the core conundrum of depression. They are the exact opposite of the optimism, energy, and a willingness to make changes that would help a person get out of a bad situation. However, there are situations in which active efforts just make things worse. One . . . is when challenging a dominant figure starts fights that cannot be won. In this situation, it is far better to inhibit striving and signal submission and a wish for reconciliation. Another situation is the failure of a major life enterprise. The pursuit of large goals requires constructing expensive social enterprises that are difficult to replace—marriages, friendships, careers, reputation, status, and group memberships. Major setbacks in these enterprises precipitate life crises. In such situations, it is often useful to inhibit any tendency to shift quickly to a different endeavor. The start-up costs for a new enterprise are huge, there is often no certainty that another enterprise can be found at all, and the attractiveness of alternatives may be illusory. Hastily giving up on an unsatisfying marriage or job often takes a person out of the frying pan and into the fire. In this situation, pessimism, lack of energy, low self-esteem, lack of initiative, and fearfulness can prevent calamity even while they perpetuate misery. There are also many other kinds of unpropitious situations, such as lacking a viable life plan or some crucial resource or being so stressed that striving would cause bodily damage. Just as anxiety inhibits dangerous actions, depression inhibits futile efforts.
. . . When depression is . . . seen as a state shaped to cope with unpropitious situations, it is clear how it could be useful, both to decrease investment in the current unsatisfying life enterprise and also to prevent the premature pursuit of alternatives. Failure to disengage can cause depression, and depression can make it harder to disengage. This may explain why the low-mood system is so prone to getting stuck in positive feedback loops. Mood dysregulation may now be so prevalent because we are bereft of kin, beliefs, and rituals that routinely extracted our ancestors from such cycles. Also, the costs of low mood may be small compared with those of inappropriate high mood, so in certain situations the “smoke detector principle” biases the system toward low mood.
Usually, the dilemma is resolved by changing or accepting the current situation or by moving on. When it is not, serious pathology may arise. The argument in this article has so far been presented in the cold quasieconomic terms of behavioral ecology. However, for most people the resources at issue are relationships that are mediated not by calculated reciprocity, but by powerful emotional commitments. To break such commitments and turn energies elsewhere is far different from just moving to a different foraging patch.
Nesse also points out that the high prevalence of depression suggests that it sometimes has adaptive value:
The epidemiology of mood disorders offers other clues. If depression were rare, like schizophrenia, and had symptoms unrelated to the experiences of most people, this would suggest it was a disease unrelated to any defense. In fact, major depressive disorder affects about 10% of the US population in a year. Depressive syndromes that do not meet diagnostic criteria are even more common. Furthermore, there is no point of rarity in the distribution that can differentiate pathologic from nonpathologic depression, and subjects move frequently between syndromal and subthreshold depression over time. Also, the incidence of depression is highest at the ages where reproductive value peaks, a pattern characteristic of few diseases.