Beyond the Chemical Imbalance: Looking to the Past to Understand the Mental Health Crisis

We are living in an era of unparalleled prosperity, driven by advances in technology that have made the basic necessities of life—food, water, shelter—widely accessible to many. Through the interwoven threads of infrastructure, we have entered a new era in which most people no longer have to struggle for physical survival. Instead of toiling the land or hunting game, we take trips to the grocery store; water is pumped straight into our home, and the only thing standing between us and shelter is often a hefty downpayment.

Life in America has generally become easier due to technological advancements. With convenience right at our fingertips, it seems paradoxical that, despite our relative prosperity, we suffer some of the highest rates of mental illness compared to any other part of the world, with more than 1 in 5 US adults living with mental illness. This raises a crucial question: how is it that despite our technological advancements and material well-being, a vast majority of us are likely to experience serious and debilitating mental conditions in our lifetimes?

Traditional psychiatric explanations attribute this rise in mental illness to chemical imbalances in the brain. However, this theory does not fully explain why mental health disorders are so widespread, especially in societies that have made such a significant advance in living standards. If chemical imbalances were truly the cause, it seems unlikely that millions of individuals would have the same biochemical makeup that predisposes them to conditions that make survival difficult. If that were the case, most of us would not be sitting here today.

To understand the rise in modern mental health issues, we must look beyond the chemical imbalance theory and explore the social and environmental factors contributing to these high rates of mental disorders. One perspective that sheds light on this issue is the evolutionary mismatch theory, which considers the disconnect between our biological and genetic makeup and the world we live in today. By exploring this theory, we can begin to understand the deep relationship between physical and mental well-being.

Evolutionary Mismatch: The Shift in Environment and Survival

The evolutionary mismatch theory posits that many contemporary health issues stem from the disconnect between the environments our ancestors adapted to and the world that we live in today. The lives of our ancestors have shaped the psychological and physical mechanisms that helped them solve the wide range of adaptive challenges they faced. Our bodies and minds evolved to thrive in an environment that is vastly different from the one in which a majority of us now live.

To understand the depth of this disconnect, imagine human history on a 24-hour clock where each hour represents 100,000 years. If human history began at midnight, we would have lived as hunter-gatherers for nearly the entire day up until about 11:54 p.m., when agriculture began and modern civilization developed. In fact, our hunter-gatherer ancestors had practiced the most successful and longest-lasting lifestyle in human history. Despite the technological advancements of today, our bodies have not had sufficient time to adapt to the drastic changes in our environment. Our most notable adaptations have occurred over several generations, but the rate of change of modern life has far surpassed the human’s ability to transform through the gradual process of evolution by natural selection. For all intents and purposes, our biological makeup is most similar to that of our hunter-gatherer ancestors.

Under this light, the violence of modernity becomes even more apparent. The agricultural revolution that occurred 12,000 years ago significantly changed the way we eat, the way we live, and the way we work. More recently, the industrial and digital revolution have changed the way we communicate. Our DNA carries instructions on how to navigate these aspects of life, but we now face a dilemma: the instructions that once served us well are now leading us astray. Instead of viewing modern mental illnesses as isolated phenomena, it may be more useful to adopt a unifying approach that considers the differences between how we lived in the past and how we live today.

Evolutionary mismatch theory does just that by providing the coherent glue that binds together the causes of mental illnesses into one framework. To better understand how this changes our perspective on mental illness, let’s look at one of the most pressing mismatches: modern diets and sedentary lifestyles.

The Modern Health Crisis: Diet and Physical Inactivity

Modern Americans are increasingly overfed, malnourished, and sedentary. Each one of these factors has an impact on how we feel and how we relate to the environment around us. Each one of the factors stands in deep contrast to the ways in which we were evolved to live. For example, what if I told you that your sweet tooth wasn’t a fault in your character but rather a biologically advantageous adaptation that helped our ancestors survive?

We live in a time when most of the things on the grocery shelf are packed with sugar, salt, and fat. While these calories are abundant now, they haven’t always been. It used to be that nutritious food was in short supply; our ancestors would have to take the time to hunt and forage for what they could find. In order to make this process as efficient as possible, our taste buds have evolved to crave food that is high in fat, salt, and sugar. We naturally prefer to eat these things without restraint; however, our bodies evolved to process them in low and naturally occurring doses. Unfortunately, this trait has been exploited by modern technology, which makes calorie-dense food readily available.

Today we are surrounded by processed foods that encourage overconsumption. Our food preference mechanism now induces us to eat more than our physiological systems can handle. This causes chronic issues such as tooth decay, obesity, and diabetes and has been shown to contribute to the worsening of mental health.

It is no coincidence that this rise in lifestyle diseases that are induced by poor dietary habits is positively correlated with the rise in mental disorders. In studying the relationships between diet and mental health in children and adolescents, Adrienne O’Neil discovered that there was evidence of a correlation between unhealthy diets and poor mental health. Habitual consumption of processed foods was associated with a greater risk for depression and anxiety. Poor diet and nutrition have been linked to biological processes underpinning depression, such as inflammation. Chronic inflammation is thought to contribute to the onset and maintenance of mental health disorders, as well as other chronic noncommunicable diseases such as cardiovascular diseases and diabetes. A dietary pattern consisting of vegetables, fruits, beef, lamb, fish, and whole grain foods is associated with lower inflammatory markers and improved mental health outcomes. These dietary patterns can also help protect against age-associated pathophysiological and cognitive changes.

In these ways and more, dietary factors may modulate the underlying neurological and cognitive changes in the brain that affect our psychological systems. So as it turns out, this dietary mismatch between our evolutionary past and our technologically inundated present is a key factor not only in physical illnesses but also in mental health.

With this in mind, it becomes hard to ascribe the cause of our mental disorders as a chemical imbalance happening solely in the brain of an individual. While yes, the cause of mental disorders may be biological, this biology cannot be separated from the context in which it was created. By acknowledging the relationship between our past and our present, it becomes apparent that our environments have far more impact on our mental health.

The Rise of the Sedentary and its Impact on Mental Health

Another significant factor contributing to the rise in mental health issues is the increase in sedentary lifestyles. Sedentarism is a lifestyle characterized by very little to no physical activity. It’s common to think of not wanting to work out as some type of moral failing and an indication that one is lazy and lacks discipline. Within this framework, the onus to exercise is placed on us as individuals rather than the environment around them that influences their behavior.

In the light of an evolutionary perspective, it becomes clear why less and less people move today; there is simply no incentive to do so. All animals, including humans, are adapted to be physically active in order to acquire resources and mates as well as to avoid being killed by predators. Our human ancestors are well known for their endurance; their days consisted of long-distance walking and running in the heat, digging up root plants, climbing trees for fruits, and carrying and throwing projectiles fast and hard to hunt game. It was normal for our hunter-gatherer ancestors to walk an average of 5 to 9 miles per day to forage enough food to survive, carrying babies and food supplies in tow as well. When they were not moving or working for their survival, they were resting, conserving their energy and avoiding any extraneous effort in an attempt to survive long periods without food. Natural selection has therefore come to favor inactivity whenever possible as a means of conserving energy.

People today move less and less because there is no immediate survival need for it. As a result, there have been serious consequences for both physical and mental health. Our muscles, bones, and nervous system all require physical activity to maintain proper functioning. Our muscles consume about 40% of our body’s resting metabolic rate. When the body notices that these muscles are not being put to use, the muscle begins to hypertrophy to allow the body to conserve its energy.

A majority of the systems in the body react to physical activity in a similar fashion. For example, physical activity generates mechanical stress in the skeleton that is necessary to stimulate the bone deposition and repair mechanisms that make bones strong and healthy. Persistent physical inactivity means that the mechanisms are not triggered often enough, which leads to weak bones and increases the risk of osteoporosis and other previously uncommon diseases. Similar things occur in the nervous system; physical activity acts on the nervous system to increase neuronal function and neuroplasticity, which explains why physical inactivity is correlated with poorer mental health. In fact, it has been suggested that regular physical activity can enhance mental wellness just as equally as psychotherapy and psychiatric medication.

Several epidemiological studies have proven that exercise has decreased the prevalence of symptoms related to depression, panic disorder, social phobia, and substance abuse disorder. Just 20–40 minutes of aerobic exercise can improve an individual’s mood for several hours. This is because exercise induces changes in different neurotransmitters, such as serotonin and endorphins, which directly influence our mood. This triggers a positive feeling in the body that is often referred to as the “runners high.” The best part is that the release of these feel-good chemicals does not lead to addiction compared to other psychiatric medications. Regular exercise can reduce stress, ward off feelings of anxiety and depression, boost self-esteem, and improve sleep.

The systems in our body need physical activity to develop the body’s normal capacity; in the absence of the necessary physical activity, our bodies fail to develop in the ways that they need to in order to promote our proper functioning and well-being. Our modern chronic and non-infectious diseases have become more common and severe because humans have never evolved to be this sedentary.

Physical Health is Mental Health

The idea present in evolutionary mismatch theory supports the budding conversation about the deep connection between our minds and our bodies. More and more, we are realizing that a cognitive, top-down approach is not enough when considering the drastic rise in mental disorders that we are dealing with today. This problem is not one that can be understood through a purely biological or psychological lens.

While genetics and brain chemistry do play a role, by individualizing and medicalizing the reality of human suffering, we are leaving out the subtle nuances that emerge when we consider our context and history as a species. Evolutionary mismatch theory forces us to question whether these categories of depression and anxiety are inherent to individuals or a byproduct of the individual existing in an environment that is not conducive to their well-being.

Diet and exercise are just two of the most prominent ways in which our genetic past is impairing our ability to healthily function in our modern society. By examining how our brains were adapted to function, we move closer to understanding who we actually are as humans. To truly address the mental health crisis, we must shift our focus from purely biological explanations to a broader, more holistic understanding that considers the deep-rooted disconnect between our evolutionary past and the modern world. By doing so, we can begin to craft solutions that address the root cause of mental illness and promote better physical and mental health for all.