Nesse (2000) suggests that depression, a disorder that affects millions of people worldwide each year, may in fact confer some adaptive benefit. He hypothesizes that because depression/low mood promotes avoidance and withdrawal, it may serve as a useful mechanism in situations in which taking action may be risky.
However, serious depression (not just “low mood”) is not a response that can be clicked on or off. It is what occurs when an individual is exposed to high levels of chronic stress. Many of the physical symptoms of depression—lethargy, decreased appetite, inability to concentrate, loss of libido—occur as a result of the long-term suppression or activation of various systems in the body by stress hormones. Unlike the flight-or-flight response—which confers immediate action when you’re, say, running away from a lion—chronic stress results in a state of “learned helplessness.”
Depression, too, carries with it a whole host of nasty consequences. It increases the likelihood of heart disease, impairs memory function, and wrecks the immune system. Moreover, depression can last for years. If depression were truly adaptive, would it not only last for a few months to a couple years, then cease (bereavement, in fact, does follow this timeline but is considered distinct from clinical depression)?
Also important to note is the occurrence of suicidal thoughts and behavior in conjunction with depression. Suicide as a result of depression is, admittedly, rare. Yet, it nonetheless occurs and is a phenomenon Nesse notably excludes in his discussion. While suicide does not necessarily result in a fitness of zero, it is difficult to argue that such behavior is not maladaptive.
Is depression itself maladaptive then? There is strong evidence that supports the maintenance of certain diseases in the population for adaptive reasons, the most notable example being sickle-cell anemia. Carriers for sickle-cell anemia are somewhat more immune to malaria than those without the allele. However, those carrying both recessive alleles have the disease.
Low mood, then, could be adaptive with depression being low mood in its disease state.
Moods and emotions are what allow us to interact with and experience the world. They are what make the good bits and the not-so-good bits in life meaningful experiences. Grief and sadness have their place alongside bliss and delight. Depression, the absence of emotion, can hardly said to be living at all.
I’ve included below a TEDtalk. It’s given by writer Andrew Solomon and is one of the best descriptions of the experience of depression I’ve come across.