You want to feel normal and you want to be able to enjoy your life but there is something crippling inside you and you can’t help but feel like you don’t deserve happiness. You are not alone – depression is experienced by one in six people1 and there is help available for them and for you.
Just as the environment surrounding you is stochastic, depression is largely unpredictable and can arise at any time for anyone. From a general standpoint, depression is defined as a medical illness caused by ranging factors related to neurological biochemistry, genetic predispositions, individual personalities, and environmental factors. Each individual experiences the symptoms of depression differently but the most common ones include fatigue, melancholy, and thoughts of self-harm. It seems paradoxical that humans as a species should suffer from an illness with consequences so maladaptive that they can be life-threatening. Moreover, it is not an illness that is a function of senescence or an external pathogen, but it is an illness that affects our minds. Your mind is essential to your survival and reproduction – why have the pressures of evolution left you so vulnerable and unhappy?
Evolutionary biology has theorized that depressive behaviour is an adaptive trait, meaning that it provides the bearer with a selective advantage in survival and reproduction. The ‘behavioural shutdown’ model is one possible explanation for the adaptivity of depressive behaviour. It suggests that when the surroundings are harsh and unfavourable, people should become inactive – activity in an environment where there is no benefit will be detrimental to your evolutionary fitness, which is a metric for the magnitude of genes contributed to future generations by an individual. To provide a basis for this theory, a study used a state-dependent model to show that organisms will cease activity and wait for more favourable environments to start foraging or reproducing. This conceptualizes the idea that those who suffer depression tend to play it safe — fear of the unknown encourages them to hold back.
For instance, you are a salesman and the majority of your income is based on commission, but the market for your product is currently down. You can spend more time working, but the probability of you making more money is very low. In this situation, it would be more advantageous for you to work less because the reward will be the same either way. Assuming that your feelings are a robust means of judging appropriate behaviour, this hypothesis would suggest that depression is an advantageous response to a seemingly unyielding environment.
Another study was conducted using a synthetic model system based purely on individual behaviour. Theoretically, a person was repeatedly presented with an arbitrary task and two different ways to respond – either to put in the effort and try to complete the task or be inactive and rest. If the individual invested effort which came at a substantial cost, the outcome was either success, which resulted in a net benefit and up-to-date information about the environment, or failure, in which case the effort expended was wasted but information was still provided. Using probability calculations, this study concluded that when a person is poorly informed, they can remain in an inactive rest even if their surroundings are full of opportunities for net benefit. This evidence supports the adaptive theory for depression but in order for the study to achieve these results, many assumptions were made that are not completely applicable or translatable to depression in the real world.
If the environment were to improve, will depression go away? This model does not directly address the persistence of depression, but we are not perfect, and we cannot always have complete knowledge of our stochastic surroundings. Perhaps, if we were always perfectly informed when it is beneficial for us to be active and when it is not, depression would act in a predictable manner.
In addition to the behavioural shutdown hypothesis, many other hypotheses exist such as the ‘analytical rumination’ hypothesis which suggests that people in a depressed state are more intelligent because they are more analytical than the average person. The major gap that these hypotheses do not consider is the real-world situation where depression can persist even if the person’s environment is optimal and their life has seemingly no external reasons for unhappiness. There is sufficient evidence to support the theory that depression is a relic of our evolutionary history because it might have been advantageous, but research has not yet been able to translate this insight into a clinical setting.
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