It must be incredibly difficult to imagine the maddening reality of living with a mental illness for someone who has never experienced it first hand. We all feel blue from time to time, but few ever experience the debilitating inability to feel joy, constant fatigue, and mind-numbing impediment of thought accompanied by major depressive disorder. William Styron once described it as being attached to a bed of nails which one carries around wherever they go, and in my experience this is strikingly accurate.
Yet for all its unpleasantness the noonday demon seems to pose an evolutionary paradox. Darwin’s legacy was that evolutionary pressures shape not only our physical characteristics but our mental and behavioural processes as well. This being the case, how is it that an illness characterized by a myriad of symptoms so obviously detrimental to evolutionary fitness – decreased cognitive function, a loss of interest in sex, socializing, and exercise, not to mention suicide – has persisted?
Not only has depression not been wiped out through the course of natural selection, it is now – and I believe rightly so – considered an epidemic. The global burden of depression is soaring; the latest estimates by the World Health Organization place the global prevalence of depression at three hundred and fifty million worldwide , and in the last forty five years alone the annual rate of suicide has increased by sixty percent . Despite our best efforts in the development of behavioural therapy, pharmacological treatment, and psychological theory the depression epidemic shows no signs of letting up. We are losing the fight against depression.
Our typical point of view is that, simply by intuition, something as inherently painful and debilitating as depression must represent a defect, a failure of the brain or mind to function correctly. Yet could it be that our inability to rein in the toll of depression is due to a complete misunderstanding of its very nature? A new wave of scientists are starting to believe so.
Dr Jonathan Rottenberg, author of “The Depths: The Evolutionary Origins of the Depression Epidemic” argues that “doctors and therapists today invariably assert that the why of the symptoms resides in a deficiency”. The deficiency – be that of a neurotransmitter, parental love, or close relationships – depends of course upon the orientation of the doctor or therapist, but the fundamental theory remains the same.
Darwin may have told us that our mental processes are shaped by behavioural pressures, which would seem to support the depression-as-defect model, but he also said that “pain or suffering of any kind… is well adapted to make a creature guard itself against any great or sudden evil”. The defect approach is inherently flawed due to the fact that many inherently unpleasant symptoms such as nausea, pain, and fatigue, are themselves – although aversive and disruptive to day to day functioning – actually advantageous. By its very unpleasantness nausea conditions us to avoid eating foods that make us sick, just as pain teaches us to avoid touching a hot stove.
Not only is the popular approach to depression flawed, it may also be causing more harm than good. By insisting that there is something intrinsically wrong with victims of depression the defect model propagates the stigma associated with mental illness, which may cause many sufferers to avoid seeking potentially lifesaving treatment. Additionally – although it is almost certain that many cases of depression are at least partly manifestations of an underlying brain pathology – continually insisting that depression is a simple chemical imbalance may offer an easy way out for many afflicted, causing the denial and avoidance of the real precipitating factors such as unsatisfying relationships and life circumstances. Commonly prescribed antidepressants such as selective serotonin reuptake inhibitors are increasingly used as a front line “band-aid” treatment of depression, however the efficacy of these medications leaves much to be desired. In many cases medication offers no more relief from depression than placebo .
These arguments form the basis of the alternative hypothesis proposed by Rottenberg – that depression may actually be an adaption geared towards survival rather than a defect. The alternative approach, argues Rottenberg, lies in a burgeoning field known as affective science, the study of moods. Affective scientists are hard at work addressing the age old question – first considered by Aristotle in his Nicomachean Ethics – of what separates a functional emotion from a dysfunctional one. It must also address the question of what distinguishes a low mood from a clinically significant depression. In order to address these questions we must first lay out some definitions of the two dimensions of affect; emotion and mood.
Emotions – such as happiness, grief, ecstasy, or terror – are experienced as situationally appropriate changes in thought, perception, behaviour, and arousal which arise as an organism encounters meaningful stimuli. These emotional responses prepare an organism to respond to its environment in a way that has “generally facilitated the survival of the species and individuals over evolutionary time” . Moods differ from emotions in that they are longer lasting and slower moving mental states, triggered by less specific events. Moods tend to colour experience from the background, subtly influencing the way we construe experience. As Rottenberg aptly portrays it; “If emotional reactions are like storms, then moods are like seasonal climate change.”
The mood system can be understood in terms of an evolutionary ancient behavioural guidance system. This system tracks and integrates environmental information with an awareness of the body’s internal states in order to compute a behavioural output that is favourable in terms of evolutionary fitness. In this way moods sculpt behaviour in a way that enhances the organisms likelihood of reproductive success. It is precisely this mood system that is hijacked by depression, producing states of excessive melancholy, pessimism, and an absence of vitality. Affective scientists like Rottenberg believe in the centrality of understanding mood to easing the burden depression – it is, after all, a mood disorder – whilst alternative biological, cognitive, and social models of depression place little to no emphasis on the role of mood.
One line of evidence in favour of the hypothesis that low moods can be beneficial to fitness comes from research into the influence on mood on goal management. Once we have embarked on a goal the mood system monitors progress towards its attainment. When minor obstacles arise on the path to our goal the mood system will increase efforts towards its completion, however it will place the breaks on effort in the event that it views a goal as unattainable. This is known as incentive disengagement theory, and is supported by physiological studies of blood pressure. For example, a sharp spike in blood pressure – an index of bodily mobilization – is observed when participants in a bad mood are asked to perform a difficult task. However, in the event that this task is made significantly harder the mood system is believed to de-escalate effort, and the sharp spike in blood pressure is no longer observed.
From an evolutionary perspective it makes sense that we are equipped with a system that acts to disengage us from goals deemed impossible by the mood system, thereby conserving finite resources such as time, energy, and money.
“Mood flexibly tunes behavior to situational requirements, which is what makes it so effective as an adaptation. When a situation is favorable, high moods lead to more efficient pursuit of rewards. Reward-seeking behavior is invigorated (eat grass while the sun shines). In an unfavorable situation, low moods focus attention on threats and obstacles, and behavior is pulled back (hunker down until the blizzard ends). Mood reflects the availability of key resources in the environment, both external (food, allies, potential mates) and internal (fatigue, hormone levels, adequacy of hydration), and ensures that an animal does not waste precious time and energy on fruitless or even dangerous efforts (doing a mating dance when predators are lurking).”
Jonathan Rottenberg, “The Depths”
In the event that the individual does not disengage from their ill-fated quests the low mood will continue to escalate, shifting cognition to more realistic and systematic goals . This phenomenon is explained evolutionarily by foraging theory, which states that organisms give up on foraging from a particular patch of food when the rate of return of the current patch falls below the average rate of return over all patches. In other words, foraging stops when the costs outweigh the benefits.
Although human behaviour is far more complex than the grazing activity of animals it can be understood in much the same way. Psychologists are increasingly beginning to attribute the role of the mood system to regulating goal pursuit, and emotions are thought to arise depending on an individual’s view of how a current event will influence goal attainment. Just as working to achieve a goal brings about positive emotions, failure to achieve our goals is an especially potent stimulus for negative emotions.
In light of incentive disengagement theory, Rottenberg argues that by understanding current trends in goal setting behaviour we may be able to account for the increasing rates of depression. Since the ‘70s the percentage of high school students who claim that earning a lot of money is extremely important to them has risen from sixteen to twenty-five percent, and the aspiration rate to go to graduate school has doubled. Additionally, in 2005 thirty-one percent of teenagers claimed that they were going to be famous in the future, whilst more and more claim that they will never be happy until they get “all that they deserve”. It’s not surprising to hear that such “morally corrupt” and extrinsically motivated goals of this nature are associated with lower levels of happiness and wellbeing, and it is the over commitment to such intrinsically unsatisfying goals which Rottenberg believes to be in part responsible for the depression epidemic.
But incentive disengagement is only one of many theories proposed by evolutionary psychologists to account for depression. In 2009 psychologists Paul Andrews and Anderson Thomson published an epic sixty one page tome entitled “The bright side of being blue: Depression as an adaption for analyzing complex problems”. Much like Rottenberg, Andrews and Thomson believe that depression needs to be understood from an evolutionary perspective, and in doing so proposed the analytical rumination hypothesis. This is an approach which realizes that many cases of depression are catalyzed by severe social stressors – a failed marriage or the loss of a job. As the patient falls into a deep depression they often ruminate – literally “chew over” – the precipitating circumstances, continually mulling over their situation in life and what they could have done differently.
That rumination is a common symptom of depression was not a breakthrough theory, rather it is the opinion that this rumination is adaptive, rather than harmful, which polarized many in the field. Rumination is typically seen as a maladaptive mental habit – actively prolonging negative moods as the patient fixates on their character flaws and the mistakes which may have led to their depression, which they believe to be complex, severe, and difficult to solve . Andrews and Thomson rejected the commonly held belief that rumination arose as the result of a biological dysfunction, instead being the product of a properly functioning stress response mechanism. Before their breakthrough paper many believed that ruminative thoughts interfered with the ability of depressed patients to solve complex problems, but many with depression have argued that their ruminations actually give them insight into the stressors which may have precipitated their condition.
In light of these attitudes, the analytical rumination hypothesis was proposed, arguing that depression is in fact a functional response to life problems, “facilitating problem solving by drawing attention to and promoting the analysis of problems”. This view is somewhat parsimonious with the incentive disengagement theory as the mood system, in conjunction with conscious decisions made through rumination, causes people to detach from unrewarding life circumstances and goals. Problems arise, however, when depression causes over-detachment, and depressed patients withdraw from aspects of the environment which may have antidepressant-like qualities, they stop exercise or socializing.
Thus the analytical rumination hypothesis rests on four foundational claims;
- “The first claim is that complex problems that influence important fitness-related goals trigger depressed affect”
- “The second claim is that depression coordinates a suite of changes in body systems that promote rumination, the evolved function of which is to analyze the triggering problem.”
- “The third claim is that, over evolutionary time, depressive rumination often helped people solve the problems that triggered their episodes”
- “The fourth claim is that depression reduces accuracy on laboratory tasks because depressive rumination takes up limited processing resources”
Evidence for these claims comes from the fact that common symptoms of depression such as anhedonia, – a loss of enjoyment in and desire to engage in pleasurable activities – psychomotor retardation, – a decrease in physical energy and movement – and changes in attentional control – the prioritization of cognitive resources to rumination – all act to facilitate a sustained analysis of the circumstances triggering their depression.
My own history with depression seems to support the combination of the incentive disengagement and analytical rumination hypotheses. I first began experiencing severe depression following a disastrous break up in which I had cheated on my girlfriend with one of my best friends. In the weeks following the breakup my mood started to slide – it seemed like all I could think about was what I could have done differently, how I could have avoided getting myself into such a terrible situation, et cetera. From the evolutionary perspective my depression was helping me to avoid making the same mistakes in the future and prepare me for bachelorhood.
Subsequent episodes of depression occurred at time in my life when I was experiencing what the legendary Viktor Frankl would consider an existential void – I was studying a degree which I had no interest in pursuing a career in, and didn’t know what I wanted to do in my life. My life was lacking meaning, and I seemed to spend the majority of my waking life ruminating on this issue. “What am I going to do with my future?” “Who do I want to be?” These sorts of questions plagued my mind to the point where I could barely think of anything else, and I believe that if not for my – although incredibly painful – experience with depression, I would never have found the answers I was looking for. It was at that point in my life that I decided I would become a psychologist (it made perfect sense that given my own experience with mental illness I would go on to help others), yet months later I found myself wrapped in the depths of another depression. I wasn’t ready to commit myself to the further six years of university required to becoming a psychologist, and I wasn’t enjoying my course. So I dropped out. With the help of depression I disengaged from what was an unrealistic goal and devoted myself to my hobby – becoming a freelance writer. I’m yet to see how that turns out.
“Perhaps what we call depression isn’t really a disorder at all but, like physical pain, an alarm of sorts, alerting us that something is undoubtedly wrong; that perhaps it is time to stop, take a time-out, take as long as it takes, and attend to the unaddressed business of filling our souls.”
Lee Stringer, Unholy Ghost: Writers on Depression
There are of course many other evolutionary theories that would present depression as an adaption. Some argue that low moods sensitize people to exclusion and “social risk”, helping them to reconnect with a group, whilst others claim that depression acts as a “stop mechanism” during competition, de-escalating conflict and allowing the loser to live to fight another day. But as Rottenberg reminds us in “The Depths”, no single factor can exclusively explain the depression epidemic, “nor is there a single factor that, if changed, would reverse the epidemic”. A conclusive account of depression would include all of the biological, genetic, psychosocial, and evolutionary accounts of depression. There is no single-bullet theory, but “when the theories are arrayed together, we can begin to appreciate why low mood endures: it is a state that is potentially useful in many different situations”.
Of course not every theory applies to every depression. The analytical rumination and incentive disengagement hypotheses are built on the idea that lousy environmental circumstances precipitate depression, but this is certainly not always the case. The fact is that depression is becoming increasingly common in a time when life is only getting easier and easier. Rottenberg reminds us that “the average citizen in Western society now lives longer, is less likely to starve, and enjoys considerably greater wealth than his sixteenth-century counterpart”, yet rates of mental illness are higher than ever. In many cases rumination does serve the forward-thinking role of understanding how and why things went wrong in the past so we can avoid them happening again in the future. But the fact is that thinking about depression often only leads to more depression – thinking causes sinking – and several major studies indicate that those with a greater tendency to ruminate have longer depressive episodes, are more pessimistic in their attitudes about the future, and have a harder time recovering from environmental stressors.
However, what may be most enlightening about the evolutionary approach to depression then is not how it fills in all of the missing details (it doesn’t), but rather what they can tell us about how to deal with depression more effectively. A number of studies indicate that the more we value the pursuit of happiness, the less happy we are likely to be. Similarly, the higher we set our goals – and therefore the less likely we are to achieve them – the less likely we are to find satisfaction and wellbeing. Rottenberg argues that “setting a goal to become happier is like putting yourself on a treadmill that goes faster the harder you run”. For people that have a “strong positive ideal”, there is a much larger gap between what they actually experience and what they would like to experience – and the size of this gap predicts depression. Affective science tells us that our mood system is designed to reward the achievement of evolutionarily important goals with temporary states of euphoria, rather than giving us an endless state of bliss. But this isn’t the pessimistic argument it seems to be, it is simply realistic, and it provides us with the wisdom we need to live happier, fulfilled lives. In the words of Rottenberg, the affective science approach…
“…offers a fresh appreciation of the costs of thinking and the benefits of becoming a critical consumer of your low mood, even sometimes accepting a low mood with equanimity; why goals should aim high, but not too high; and why we should recognize that persistence in striving to achieve a failing goal can be self-defeating. It also suggests that we should avoid fixating on a specific happiness level and recognize that happiness itself is not a goal but a fleeting by-product of progress toward other goals.”
- World Health Organization. (2008). Suicide statistics: Introduction. Retrieved from http://www.who.int/mental_health/prevention/suicide/suicideprevent/en/print.html
- Olfson, M., & Marcus, S. C. (2009). National patterns in antidepressant medication treatment. Archives of General Psychiatry, 66, 848– 856
- Nesse, R. M. (2000). Is depression an adaptation?. Archives of General Psychiatry, 57(1), 14-20.
- Andrews, P. W., & Thomson Jr, J. A. (2009). The bright side of being blue: depression as an adaptation for analyzing complex problems. Psychological review, 116(3), 620.