Reflecting on this morning's usual breakfast cake brought to mind a thought that only people like myself think: the sugar in my breakfast is not sweet. Sweetness, while not a property of the sugar, is an experience generated by our mind when sugar is present on the tongue. We generally find the presence of sugar to be a pleasant experience, and often times find ourselves seeking out similar experiences in the future. The likely function of this experience is to motivate people to preferentially seek out and consume certain types of foods, typically the high-calorie variety. As dense packages of calories can be very beneficial to an organism's survival, especially when they're rare, the tendency to experience a pleasant sweetness in the presence of sugar was selected for; individuals who were indifferent between eating sand or honey were no one's ancestors.
On a related note, there's nothing intrinsically painful
about damage done to your body. Pain, like sweetness, is an important
signal; pain signals when your
body is being damaged, in turn motivating people to stop doing or get
away from whatever is causing the harm and avoiding making current
injuries worse. Pain feels so unpleasant because, if it didn't, the proper motivation would not be provided. However, in order to feel pain, an organism must have
evolved that ability; it's not present as a default, as evidenced by the
rare people born without the ability to feel pain.
As one could imagine, those who were indifferent to the idea of having
their leg broken rarely ended up reproducing as
well as others who found the experience excruciating.
Walk it off
Sensations like pain or sweetness can be explained neatly and satisfyingly through these functional accounts. With these accounts we can understand why things that feel pleasant - like gorging myself on breakfast cake - are not always a good thing (when calories are abundant), whereas unpleasant feelings - like sticking your arm in a wood-chipper - can be vital to our survival. Conversely, lacking these functional accounts can lead to poor outcomes. For instance, treating a fever as a symptom of an infection to be reduced, rather than a body's adaptive response to help fight the infection, can actually lead to a prolonging and worsening of said infection (Nesse & Williams, 1994). Before trying to treat something as a problem and make it go away just because it feels unpleasant, or not treat a problem because it might be enjoyable, it's important to know what function those feelings might serve and what costs and benefits of reducing or indulging in them might entail. This brings us to the omnipresent subject of unpleasant feelings that people want to make go away in psychology: depression.
Depression, I'm told, is rather unpleasant to deal with. Most commonly triggered by a major, negative life event, depression leads to a loss of interest and engagement in almost all activities, low energy levels, and, occasionally, even suicide. Despite these apparent costs, depression continues to be a fairly prevalent complaint the world over, and is far more common among women than men. Given its predictability and prevalence, might there be a function behind this behavior? Any functional account of depression would need to both encompass these known facts, as well as purpose subsequent gains that would tend to outweigh these negative consequences. As reviewed by Hagen (2003), previous models of depression suggested that sadness served as a type of psychic pain: when one is unsuccessful in navigating the social world in some way, it is better to disengage from a failing strategy than to continue to pursue it, as one would be wasting time and energy that could be spent elsewhere. However, such a hypothesis fails to account for major depression, positing instead that major depression is simply a maladaptive byproduct of an otherwise useful system. Certainly, activities like eating shouldn't be forgone because an unrelated social strategy has failed, nor should one engage in otherwise harmful behaviors (potentially suicidal ones) for similar reasons; it's unclear from the psychic pain models why these particular maladaptive byproducts would arise and persist in the first place. For example, touching a hot pan causes one to rapid withdraw their hand, but it does not cause people to stop cooking food altogether for weeks on end.
Hagen (2003) puts forth the idea that depression functions primarily as a social bargaining mechanism. Given this function, Hagen suggests the following contexts should tend
to provoke depressive episodes: a person should experience a perceived
negative life event, the remedy to this event should be difficult or
impossible to achieve on their own, and there must be conflict over
other people's willingness to provide assistance in achieving a remedy. Conflict is ubiquitous in the social realm of life; that much is uncontested. When confronted with a major negative life event, such as the death of a spouse or the birth of an unwanted child, social support from others can be its most important. Unfortunately for those in need, others people are not always the most selfless when it comes to providing for those needs, so the needy require methods of eliciting that support. While violence is one way to make others do what you'd like, it is not always the most reliable or safest method, especially if the source you're attempting to persuade is stronger than you or outnumber you. Another route to compelling a more powerful other to invest in you is to increase the costs of not investing, and this can be done by simply withholding benefits that you can provide others until things change. Essentially, depression serves as a type of social strike, the goal of which is to credibly signal that one is not sufficiently benefiting from their current state, and is willing to stop providing benefits to others until the terms of their social contract have been renegotiated.
"What do we want? A more satisfying life. When do we want it? I'll just be in bed until that time...whatever"
Counter-intuitive as it may sound, despite depression feeling harmful to the person suffering from it, the function of depression would be to inflict costs on others who have an interest in you being productive and helpful. By inflicting costs on yourself (or, rather, failing to provide benefits to others), you are thereby motivating others to help you to so they can, in turn, help themselves by regaining access to whatever benefits you can provide. Then again, perhaps this isn't as counter-intuitive as it may sound, taking the case of suicide as an example. Suicide definitely represents a cost to other people in one's life, from family members, to spouses, to children, to friends, or trade partners. It's much more profitable to have a live friend or spouse capable of providing benefits to you than a dead one. Prior to any attempt being made, suicidal people tend to warn others of their intentions and, if any attempt is made, they are frequently enacted in manners which are unreliably lethal. Further still, many people, whether family or clinicians, view suicidal thoughts and attempts as cries for help, rather than as a desire to die per se, suggesting people have some underlying intuitions about the ultimate intentions of such acts. That a suicide is occasionally completed likely represents a maladaptive outcome of an evolutionary arms race between the credibility of the signal and the skepticism that others view the signal with. Is the talk about suicide just that - cheap talk - or is it actually a serious threat?
There are two social issues that depression needs to deal with that can also be accounted for in this model. The first issue concerns how depressed individuals avoid being punished by others. If an individual is taking benefits from other group members, but not reciprocating those benefits (whether due to depression or selfishness), they are likely to activate the cheater-detection module of the mind. As we all know, people don't take kindly to cheaters and do not tend to offer them more support to help out. Rather, cheaters tend to be punished, having further costs inflicted upon them. If the goal of depression is to gain social support, punishment is the last thing that would help achieve that goal. In order to avoid coming off as a cheater, a depressed individual may need to forgo accepting many benefits that others provide, which would help explain why depressed individuals often give up activities like eating or even getting out of bed. A more-or-less complete shutdown of behavior might be required in order to avoid coming off as a manipulative cheater.
The second issue concerns the benefits that a depressed individual can provide. Let's use the example of a worker going on strike: if this worker is particularly productive, having him not show up to work will be a genuine cost on the employer. However, if this worker either poorly skilled - thus able to deliver little, if any, benefits to the employer - or easily replaceable, not showing up to work won't cause the employer any loss of sleep or money. Accordingly, in order for depression to be effective, the depressed individual needs to be socially valuable, and the more valuable they are seen as being, the more of a monopoly they hold over the benefits they provide, the more effective depression can be in achieving its goal. What this suggests is that depression would work better in certain contexts, perhaps when population sizes are smaller and groups more mutually dependent on one another - which would have been the social contexts under which depression evolved. What this might also suggest is that depression may become more prevalent and last longer the more replaceable people become socially due to certain novel features of our social environment; there's little need to give a striking worker a raise if there are ten other capable people already lined up for his position.
You should have seen the quality of resumes I was getting last time I was single.
That depression is more common among women would suggest, then, that depression is a more profitable strategy for women, relative to men. There are several reasons this might be the case. First, women might be unable to engage in direct physical aggression as effectively as men, restricting their ability to use aggressive strategies to gain the support of others. Another good possibility is that, reproductively, women tend to be a more valuable resource (or rather, a limiting one) relative to men. Whereas almost all women had a valuable resource they could potentially restrict access to, not all men do. If men are more easily replaceable, they hold less bargaining power by threatening to strike. Another way of looking at the matter is that the costs men incur by being depressed and shutting down are substantially greater than the costs women do, or the costs they are capable of imposing on others aren't as great. A depressed man may quickly fall in the status hierarchy, which would ultimately do more harm than the depressive benefits would be able to compensate for. It should also be noted that one of the main ways depression is alleviated is following a positive life change, like entering into a new relationship or getting a new job, which is precisely what the bargaining model would predict, lending further support to this model.
So given this likely function of depression, is it a mental illness that requires treatment? I would say no to the first part and maybe to the second. While generally being an unpleasant experience, depression, in this model, is no more of a mental illness than the experience of physical pain is. Whether or not it should be treated is, of course, up to the person suffering from it. There are very real costs to all parties involved when depression is active, and it's certainly understandable why people would want to make them go away. What this model suggests is that, like treating a fever, just making the symptoms of depression go away may have unintended social costs elsewhere, either in the short- or long-term. While keeping employees from striking certainly keeps them working, it also removes some of their ability to bargain for better pay or working conditions. Similarly, simply relieving depression may keep people happier and more productive, but it may also lead them to accept less fulfilling or supportive circumstances in their life.
References: Hagen, E.H. (2003). The bargaining model of depression. In: Genetic and Cultural Evolution of Cooperation, P. Hammerstein (ed.). MIT Press, 95-123
Nesse, R.M., & Williams G.C. (1994). Why We Get Sick: The New Science Of Darwinian Medicine. Vintage books.