Until recently, a central tenet of biomedical psychiatry was that depression is caused by low serotonin levels. A recent study has debunked that claim, to great publicity. In response, some researchers have called for “doubling down” on the search for biological causes of depression. I want to present something radically different.

What if depression is purposeful, rather than pathological? What if it’s a designed response to a problem of life, not a disease?

Evolutionary Psychiatry

Some researchers over the past 30 years have argued that depression isn’t a disease but an evolved adaptation. Though there are a number of specific hypotheses, they all share the idea that depression is nature’s way of telling us that something in our lives isn’t going well—particularly with our social interactions.

One of the first of these hypotheses was the social competition hypothesis. In this view, depression originated in prehistoric competitions over resources. When I find myself “outcompeted” by another person for a prized resource, depression saps my incentive to fight.

A second, more general, view is that depression is nature’s way of helping us detach from unrealistic life goals. Low mood takes away my motivation to strive for unrealistic goals and lets me focus on realistic ones.

A third hypothesis is called the social risk theory. This view sees depression as a response to the threat of exclusion. Through depression, I communicate that I’m a “low social risk” to others, and I convey the need for additional support from close friends and relatives.

A fourth is the analytical rumination hypothesis. It stems from the observation that people with depression often mull over their perceived failures. This suggests that the purpose of depression is to help us focus attention on complex social problems.

Evidence for the Design Hypothesis

Unfortunately, evolutionary hypotheses cannot be tested directly. They require drawing evidence from a large number of different areas. And, the fact is, there’s not a lot of funding available for testing them.

Still, there are some intriguing lines of evidence suggesting that depression is an adaptation, not a disease (see del Giudice 2018 for a review).

Depression occurs worldwide, with a high incidence and strong genetic risk. That’s often a sign that it’s playing some important role in our lives. If it were a disease, we wouldn’t expect it to be so common, especially among people of reproductive age.

It’s long been recognized that depression is more likely to be triggered by perceived social losses, rather than nonsocial losses. It’s more likely to be triggered by factors such as divorce or humiliation, rather than losing a house or car.

Depression shows high comorbidity with other disorders with a strong social component, such as social anxiety disorder. Also, depressed people tend to be highly vigilant to the threat of social rejection.

Even if depression is an adaptation, that doesn’t mean it always has a positive outcome. In some cases, depression can become unregulated and spiral into something quite destructive.

For example, depression can have a “self-reinforcing” character. Depression can lead to social isolation, which can reinforce depression. Rumination over one’s perceived failures can reinforce patterns of negative thinking.

Moreover, even if depression helped our prehistoric ancestors, that doesn’t mean it’s always useful today. For example, if depression is caused by having unrealistic life goals, it doesn’t help that we’re surrounded by media telling us our worth as human beings is connected to our accomplishments.

Changing Perspectives, Changing Treatments

If depression is part of nature’s design, what does that mean for research? What does it mean for treatment?

First of all, it does not always mean people should stop taking medications. The fact that something is a designed response of nature is compatible with taking pills to ease the discomfort it creates— just like we take aspirin for fever or an epidural injection for childbirth. Instead, what it means is that, in the course of treatment, we should ask: What’s my depression a response to? What in my life isn’t going the way it should?

More specifically, we should look carefully at social causes. We might consider the content of depressive rumination to see whether it holds clues to the area of life to which depression is responding. Just because depression is a response to a problem, that doesn’t mean its source will be obvious to people without help from a therapist. The idea that depression is an adaptation is best seen as a tool for supplementing existing treatments rather than rejecting them entirely.

Intriguing recent evidence suggests that seeing depression as a designed response to a life problem, rather than a disease, can actually lead to better treatment outcomes. It can lead depressed people to feel more hopeful about the possibility of getting well and less stigma about their depression. The idea of depression as a designed response to the problems of life is part of a greater paradigm shift that’s currently taking place in Western psychiatry, from what I call “madness-as-dysfunction” to “madness-as-strategy” (Garson 2022).

In this new paradigm, we’re able to see some mental illnesses not as bugs, but as features—as potential advantages, not disadvantages.

The traditional belief in psychiatry is that depression is caused by low levels of serotonin, however a recent study has challenged this idea. Some researchers continue to search for biological causes of depression. However, an alternative perspective suggests that depression may not be a disease, but rather a purposeful response to a problem in life.

Evolutionary Psychiatry

The idea that depression is an evolutionary adaptation, rather than a disease, has been proposed by some researchers in the field of psychiatry. This theory suggests that depression is a natural response to issues in one's social interactions and life goals. Four specific hypotheses have been proposed, including the social competition hypothesis, which suggests that depression arose as a response to prehistoric competition over resources, the detachment from unrealistic life goals hypothesis, which suggests that depression helps individuals focus on realistic goals, the social risk theory, which posits that depression is a response to the threat of exclusion, and the analytical rumination hypothesis, which suggests that depression helps individuals focus on complex social problems.

The theory that depression is an evolutionary adaptation, rather than a disease, suggests that it serves a purpose in response to problems in our social interactions. This hypothesis cannot be directly tested and lacks significant funding for research. However, there are indications that support this theory such as the high incidence and genetic risk of depression, its tendency to be triggered by social losses, and its high comorbidity with other social disorders such as social anxiety disorder. However, it's important to note that if depression is an adaptation, it can also become destructive and spiral out of control.

The idea that depression is a natural response to problems in life, rather than a disease, can lead to better treatment outcomes and reduce the stigma associated with it. This is part of a larger shift in Western psychiatry from viewing mental illnesses as dysfunction to viewing them as a strategy for coping with life issues. This perspective does not mean people should stop taking medication, but rather encourages individuals to examine the underlying causes of their depression and to consider social factors. This approach can be used to supplement existing treatments rather than replace them.