This is an email from Inside Your Head 🧠, a newsletter by Elemental.

Did Your Brain Evolve to Be Depressed?

An evolutionary explanation of mental illness

Credit: Image by cuppyuppycake / Getty Images

This is a modified excerpt from Inside Your Head 🧠, a weekly newsletter exploring why your brain makes you think, feel, and act the way you do, written by me, Elemental’s senior writer and a former brain scientist. Subscribe here so you won’t miss the next one.

I’m fascinated by the field of evolutionary psychology, which you can think of as the eventual landing site of virtually every line of questioning about human behavior that starts with “why.”

Why do we give gifts for holidays and birthdays? Because we’re a social species that is hardwired to express altruism in order to increase our own chances of survival. Why do humans have tribal tendencies that can span everything from sports team affiliations to race? Because our prehistoric ancestors had to make instant judgments between friend and foe in order to survive. Why do we plan fantasy vacations to Hawaii during a pandemic? Because our brains evolved to prioritize future events so that we could appropriately prepare for them and increase our odds of survival.

These are, of course, vast oversimplifications of extremely complicated concepts that have many biological and cultural contributors. But there is a sort of satisfaction and sensibility that comes from the ultimate answer of “our ancestors evolved to be this way because it helped the human species survive.”

This rationale gets tricky, however, when discussing behaviors and traits that are thought to be disadvantageous today, most notably mental illnesses like depression.

A quick test to determine whether a behavior is inherently human and potentially evolutionarily selected for is whether it can be found in multiple places and times. Depression passes this test as depressive or melancholic symptoms have been found in virtually every continent and culture, including hunter-gatherer societies, and described for thousands of years. Depression is also extremely common, by some estimates afflicting up to half of the population over the course of their lives.

This fact raises the question of whether there might be an evolutionary advantage of depression, the rationale being that the condition would otherwise have been selected out, eliminating the genetic predisposition for a trait that, on the surface at least, appears to be disadvantageous.

One proposed explanation for depression’s evolutionary benefit is that the ruminations and obsessive thoughts that often accompany it are a form of advanced analytical thinking. Intense focus and breaking down complex challenges into smaller components are advantageous when it comes to critical thinking and problem-solving. It’s possible that ruminating enables people to better solve the problems at the root of their depression, whether it’s marital troubles, work dissatisfaction, or economic struggles.

Ironically, one common symptom of depression is difficulty concentrating, although the argument could be made that people have trouble concentrating on anything besides the focus of their ruminations. Psychologists Paul Andrews and J. Anderson Thomson even go so far as to suggest that the social isolation and anhedonia (loss of pleasure) people with depression often feel could be beneficial when it comes to avoiding distractions that draw their attention away from single-minded problem-solving.

A similar theory puts forward the idea that depression almost always stems from a negative scenario that people want to escape or rectify. Sadness and other symptoms of depression could help prompt you to change a bad situation you might have otherwise resigned yourself to.

Another potential benefit suggested by psychologists is that people who are depressed in many ways see the world more clearly than nondepressed people, and therefore they are better at assessing risk. Most people walk around with rose-colored glasses on, maintaining an optimism bias that everything will work out and that they and their loved ones are luckier than the average person. The truth, of course, is that no one is special and exempt from physics or statistics. The pessimistic shroud that depressed people are wrapped in is actually a more accurate assessment of the world, which could help keep them safe and increase their chances for survival.

A fourth theory is that depression is a byproduct of another genetic selection. A paper from 2013 reported that some of the gene variants that infer a higher risk for depression also affect the immune system. For example, a variant in the gene NPY raises a person’s risk for developing depression via the stress response, but it also enhances the immune system’s inflammatory response that enables it to fight off infections more effectively. As a result, a person with the NPY variant would be more likely to survive and pass on their genes despite a tendency for melancholy. Interestingly, depression is often associated with higher levels of inflammation in the body.

Evolutionary psychiatrist Randolph Nesse takes a more holistic view, saying that our brains evolved to benefit our genes — i.e. our survival, procreation, and the survival of our offspring — not to benefit our happiness or well-being.

“It gets really poignant when you ask why all of us are striving so hard for status and more money than we need,” Nesse says. “The proximate answer has to do with cultural factors and brain mechanisms, but the evolutionary factor is that natural selection has shaped us all to pursue goals that maximize our reproduction even if that makes us very unhappy.”

I want to reiterate that depression is a serious, complicated condition that affects many people in different ways and for different reasons. The idea that it might somehow have been evolutionarily advantageous at one time doesn’t mean that it is now, and it doesn’t mean that if you are depressed you shouldn’t get treatment. Life is hard, especially right now, and everyone needs and deserves help. But evolution is an interesting lens to view depression through, to normalize it, and, rather than thinking there’s something wrong with you, to examine it from the perspective of what it might be telling you.

Health and science writer • PhD in 🧠 • Words in Scientific American, STAT, The Atlantic, The Guardian • Award-winning Covid-19 coverage for Elemental

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