On the Usefulness of Depression

One question that, in recent years, has repeatedly confronted researchers in mental health regarding what is called depressive illness is the difficult-to-understand prevalence of depression in human societies. Compared with other conditions called mental illnesses, whose prevalence rarely exceeds five per cent of a population, depression in some societies has been estimated at thirty to forty per cent. In Iranian society, one sometimes has the impression that, if reliable prevalence figures existed, the proportion might be even higher. In a society such as Australia, regarded as wealthy and successful and as having relatively low levels of stress, nearly twenty per cent of people attending general practitioners either present for assessment because of anxiety and depressive problems or are currently taking antidepressants because of previous consultations. The use of psychological services is so widespread that, in my personal experience and from referring my own patients to psychology services, the waiting list to see a psychologist in the small city where I live—with a population of around seventy thousand and dozens of practising psychologists—is on average two to three months.

This unusual prevalence of depression compared with other mental illnesses has led researchers to ask whether depression might not, in principle, be a mental illness at all, but whether its fundamental function could be related to an evolutionary process in human beings.

Some symptoms of depression—such as the desire for solitude, reduced energy for general activities, reduced sexual desire and insomnia—might potentially, in some people with stronger analytical capacities, contribute to increased powers of analysis, creativity, and even greater concentration on the problems before them.

From an evolutionary perspective, it is well known that the brain’s 5-HT1A serotonin-receptor structure, a major target of antidepressant medication, has been conserved through evolution. Its similarity between simpler mammalian species such as rodents and human beings is over ninety-nine per cent. This fact, alongside the striking finding that the number of these hormone-related receptors associated with depressive processes has not decreased in human beings with the evolution of the human brain and the increasing complexity of consciousness relative to less complex animal species, but has instead increased, suggests not only a purposeful evolutionary insistence on preserving this receptor structure over millions of years but an increase in it alongside the growing complexity of consciousness.

Comparing the sleep structure of people with depression with those who do not have depressive symptoms shows an increase in REM sleep. This is the phase that contributes to the consolidation of memory, which appears related to an effort by the brain to increase analytical capacities during waking life. REM sleep is also the stage in which most dreams occur. This, too, may indicate an attempt by the unconscious mind to communicate more with the conscious mind and to send images that, from a Jungian psychological perspective, may have meaningful functions in helping us better understand the unconscious mind’s attempts at dialogue and communication.

Charles Darwin can be regarded as one of the scientists of the past three centuries who most profoundly influenced the scientific understanding of modern human beings. Through the theory of evolution, Darwin fundamentally transformed the modern view of the formation and development of life. Yet throughout his own life he was not spared severe depression. In surviving letters, Darwin refers to the depth of his depression, which on many days brought him to tears and intense sorrow. He imagined this to be evidence of his weakness because, in his view, the winners in the struggle of life were always the strong, and perhaps his own fate was merely to remain forever an admirer of the greatness of the giants of science without ever having an effect on the world. Today we know how mistaken Darwin was in judging his impact on science—and perhaps also in judging the effect of his depression on the formation and persistence of his research. In other letters, he himself described how his work and studies had become the only pleasure remaining in his life.