The Evolution of Depression
Depression is one of the most common forms of mental illness, affecting millions of people each year. Despite this, most people have not considered the evolution of depression. This line of thought goes beyond what depression is and tries to explain the why.
Specifically, this article asks: why are we vulnerable to feeling depressed in the first place? By better understanding the why, it is possible to develop a deeper understanding of what might be happening if you are experiencing depressive symptoms.
First, it’s important to point out that we are all capable of experiencing some of the symptoms of depression as a routine part of life. Low mood, sleep disturbances, changes in appetite or weight. These things are likely to happen to anyone from time to time. But why, in some people, do so many of these symptoms cluster together in what mental health professionals call Major Depressive Disorder (MDD)?
Is it possible that some of the symptoms that constitute MDD could be adaptive - contributing in some way to our success as a species? The evolution of depression can help explain why MDD exists.
It might come as a surprise, but all of the symptoms of MDD are often part of a normal, adaptive response from our body. In fact, sometimes we are supposed to get depressed. Moreover, from an evolutionary point of view, depression can be beneficial.
You might be asking, “Who holds this evolutionary point of view and how could they be so wrong?”
Well, that would be you, specifically your genes. Unfortunately, they are famously selfish and tend to prioritize their survival and reproduction over your happiness. That means that feeling bad can sometimes be “good”, at least according to your DNA.
Imagine sometime in history, your ancestor’s depressive symptoms increased the fitness, or number of children, they had. If that happened, those symptoms would be more likely to stick around in the future. If we consider the evolution of depression, this means that it is possible for depressive symptoms to be a normal, or even helpful, reaction to life events (but importantly not always).
Like any system, how our body regulates our mood is not perfect. To help understand why this happens, first, we’ll examine some of the most common symptoms of depression and imagine why under historic circumstances, they might have an adaptive function.
Then, we will look at sources of depression that routinely occur during or after normal life events to understand why a depressed state might, in some capacity, be beneficial.
A major caveat here: exploring reasons why depression might have been adaptive in the past is not to say that it is good, or still serving us in the present. MDD causes incalculable suffering to millions of people around the world - this is not beneficial. Remember, the goal here is to try to understand the evolution of depression and why it still exists, despite being so apparently harmful.
Common Symptoms of Depression
Consider some of the most common symptoms associated with depression and MDD: emotional pain, rumination, lack of concentration, guilt, weight change, loss of pleasure, changes in sleep, and exhaustion. How could any of these possibly be adaptive?
In a broad and simplified sense, the adaptive value of these symptoms can be thought of in two categories. The first is something like “Avoid That In the Future” and the second is “Wait.”
Consider pain, both physical and emotional. We do not like things that cause us pain and that’s for a good reason. Pain is a valuable form of feedback that tells us something is harmful and without it, we would not last long. Pain is how we learn to avoid damaging things in the environment. Whether it’s a hot stove or a snake bite, pain is our body’s way of telling us to probably avoid that in the future. The same is similarly true for mental or emotional feelings of pain.
What does our mind sometimes do after a painful experience? Rumination, or thinking about things repeatedly, is our brain trying to learn an important lesson. If you forget about the damaging thing, it’s more likely you’ll get hurt again. Lack of Concentration is linked to rumination. You cannot focus on anything else when your mind is preoccupied with whatever it was that caused your pain.
Guilt is a painful emotion that usually creeps up when you have done something wrong. If you steal, you might feel guilty about it afterwards. That painful guilt could be your brain telling you not to do that again. Why? Historically, in small tribes or towns where everyone knew each other, committing crimes (and getting caught) was a good way to get exiled, or worse. It makes sense that we developed an emotional moral compass to help us avoid the ire of our family and friends.
Food can be one way people try to self-soothe when they’re experiencing pain. Post-breakup ice cream is a thing. But this is just one way weight change is linked with depression. On the other hand, sometimes people lose weight when experiencing depression. This stems from a loss of appetite. Here is where we get to the “wait” response.
Imagine a time of historic scarcity, like the middle of winter, when there is essentially no food around. How useful would it be for you to be ravenously hungry? Throughout most of history, finding food took a lot of energy. It took way too long to figure out pizza delivery. In this environment, poor appetite can be a signal to wait for more plentiful times because expending precious energy now might be counterproductive.
This phenomenon is related to the symptom of low motivation or a loss of pleasure, otherwise known as anhedonia. Pleasure comes from our motivation to seek out different kinds of rewards. When the likelihood of getting a reward is low, motivation and subsequent pleasure can drop. This is another possible way the body is trying to conserve energy during perceived scarcity.
Sleep problems in depression are similar to weight change in that they can move toward either extreme. In some people suffering from depression, they develop insomnia and have trouble falling or staying asleep. This could be due to the rumination caused by a painful experience. Others go in the opposite direction and sleep too much. This could be another way the body is trying to conserve valuable energy - think of a bear hibernating for the winter.
Finally there is exhaustion. This can of course be a result of the lack of sleep you’re getting from all the rumination. Or, as you might have guessed but now, just another signal from your body to slow down, conserve energy, and wait for better times.
A Depressing Situation
What is the common link between these symptoms? What are the sources of our depression?
Let's think about this in terms of the evolution of depression. In other words, we can consider what historical circumstances might result in the symptoms of MDD clustering together.
Historically, our ancestors experienced a lot of problems, threats, loss, scarcity, and failure.
In short: stress. For the purposes of this article, stress can broadly be thought of as anything that signals to your body that it is going to have to deal with something - a problem. We respond to different stressors in different ways.
Depression is one way your body tries to solve problems or deal with stressors. What might it be trying to get us to do?
Depression, as a temporary state, could be our body trying to increase our likelihood of survival, usually by telling us to “Avoid” or “Wait.” Unfortunately for us, we tend to experience this as suffering.
Even if it doesn’t make you feel better, it can still be helpful to remember that feeling depressed can be a signal. Depression might be your body attempting to tell you something. Maybe it is a sign to avoid something in the future or try a different approach. It might be saying that you need to wait, rest, and recover.
Mixed Signals
The trouble is, during the evolution of depression, symptoms that once functioned as helpful signals are becoming more prone to malfunction in a modern environment. This can lead to chronic maladaptive depression - low mood that doesn’t go away and is not helpful.
What about modernity is depressing? If you’re a human reading this, you might already know that it is stressful. Crucially, in many cases, it is much more stressful than our bodies and minds are able to cope with. Worst of all, modern stressors have a tendency to be long lasting, not the temporary stressors we were more likely to encounter in the past. Lions get tired and stop chasing you. Your bills have infinite stamina.
The expanding list of stressors in modern society range from challenging job markets to unaffordable housing to social media feeds full of unrealistic expectations, all can contribute to perpetual states of stress.
In the modern world, the symptoms acting as useful signals from your body, through the evolution of depression, suddenly become maladaptive and no longer serve any function. Sometimes we can’t easily avoid the thing in the future or wait it out until things get better.
As a society and as individuals, we don’t seem to have much patience or tolerance for depression. There is pressure to feel good, get back to work, don’t be so down! But we should take the signals from depression seriously and listen to what our bodies are trying to tell us.
Paying attention to, understanding, and addressing symptoms of depression sooner rather than later, can help address what might be going on and avoid chronic maladaptive depression. As one broad strategy, it can be helpful to explore various lifestyle changes that can reduce or eliminate pervasive forms of chronic stress in your life.
If you need additional resources, reaching out to a qualified mental health professional, like those at The Center for Growth, can help.
