Introduction: Something is Not Working

There is a purple and maroon line that runs down the Rocky Mountain front on the CDC's map that tracks suicide mortality by state. The deep colors indicate the highest per-capita suicide rates. The top five states with the highest suicide rates are on the Rocky Mountain front (Centers for Disease Control and Prevention [CDC], 2021). A lot of theories on why suicide rates are higher along the mountain range. Some of the theories include higher elevation rates, smaller amounts of lithium salts in the water, and lower socioeconomic conditions.

As a mental health clinician located in Montana, I believe there are some truths to the above theories, but I suspect there is something more to it. I recently compared my organization's percentage of patients diagnosed with a mental health condition to national averages and what I found shocked me. The percentage of my clinic's patients diagnosed with depression were over four times the national average and most were being treated but their PHQ-9 scores did not indicate that they were improving.

After seeing the data, I started asking myself what is different about patient populations in these areas and why do they not respond to traditional treatment approaches? To answers these questions, I turned to my undergrad training in history and sociology. Through these approaches I came to believe that the answer may reside in human evolution. Specifically, what we describe as mental illness may instead be the result adaptive traits that no longer work in modern society. In this article I hope to explore how mental disorders like ADHD, autism, bipolar disorder, and psychotic disorders served an evolutionary purpose through the lens of Life History Theory.

A Different Lens to View Mental Health

Life History Theory an evolutionary theory provides a framework to explain how organisms assign limited resources to competing developmental tasks over the life span to maximize evolutionary strength. The way individuals allocate energy adds to the variability of life history strategies, which lies on a slow-to-fast spectrum. According to the theory psychological outcomes found in slower strategies are associated with farsighted behaviors including risk avoidance, optimism, and cooperation. While faster strategies are associated with shortsighted behaviors, such as impulsiveness, risk-taking and aggression (Han & Chen, 2020).

Life-history traits are often double-edged swords. Strategies can be adaptive in terms of evolutionary fitness but may be regarded as undesirable, increase vulnerability to dysfunction, and cause physiological/psychological health problems. Life history traits may also express above average levels of adaptive characteristics and result in maladaptive behaviors. Some adaptive strategies are beneficial to the fitness of all organisms but enact high costs. For example, increasing mental disorders in harsh and unpredictable environments (Han & Chen, 2020).

From an evolutionary lens, hunter-gatherers were generalists that needed to know how to do a little bit of everything to survive, which involved flexibility and adaptability. For example, nomadic individuals with ADHD may have responded better to unpredictable threats due to novelty-seeking behaviors that exposed them to different experiences and opportunities to expand their perspectives (Goldman et al., 2021).

In the US, people don't have to worry about going out into the wild to find food. Instead, it's classrooms, jobs, and other places with defined codes of behavior (Goldman et al., 2021). It is interesting how mental illness came to the forefront through Freud's work as industrialization began to spread throughout Europe. Though industrialization ultimately led to the technological revolution it ended working cycles based on sunrise/sunset and the seasons. It also gave birth to the specialist and made evolutionary traits that favor generalists obsolete.

Attention Deficit Hyperactivity Disorder

According to evolutionary thinking, behavior traits that have survived must have had adaptive value in the past. It is plausible that more adventurous individuals in hunter-gatherer societies did better in terms of having viable offspring because those individuals were more willing to explore. When researchers examined the genes of descendants of people engaged in major migrations of the distant past, they found a higher percentage of the novelty-seeking genetic variation associated with ADHD. It is suspected that being a carrier of that novelty-seeking variant might have increased the likelihood of survival by influencing individuals more inclined to seek new pastures when danger appeared and survive to pass on this variant (Swanepoel et al., 2017).

In 2012 nearly 9% of school-aged children in the US were diagnosed with ADHD. Conversely, ADHD diagnosis in France was less than 0.5%, Denmark 1%, and 3.8% in Iceland (Swanepoel et al., 2017). The higher rates of ADHD may be related to novelty seeking traits needed by European migrants to cross the Atlantic and settle in a foreign land. The trait may also explain why some were drawn to the Rocky Mountain front when it was still very much the frontier.

People with ADHD are often more sensitive to their environment. Epigenetic research demonstrates that some children are more sensitive to the influence of their environment than others. Studies suggest that successful reproduction of one's genes is more likely if one's offspring are more impacted by the current environment than others. Instead of focusing on the vulnerability genes found in individuals with ADHD researchers, educators, and clinicians should direct their focus on the plasticity of the genes (Swanepoel et al., 2017).

From the viewpoint of Life History Theory, a higher metabolism, less trust, less relaxation, more suspicion, and risk-taking might be adaptive traits for hostile environments. It is a genetic strategy that ensures short-term survival even at the cost of long-term physical and mental health. Those born into highly stressed environments tend to have a higher metabolism, more activated stress response systems, and develop fast instead of slow life history strategies (Swanepoel et al., 2017).

Researchers studied an African community that still lived a nomadic lifestyle. The study identified members of the community who displayed ADHD traits. Specifically, they studied the DRD4 7R, a genetic variant that may be linked to ADHD behaviors like novelty-seeking, greater food, and substance-use cravings. The study showed that members of the nomadic community with ADHD were better nourished than those without. It also noted that impulsive behavior recognized as a key trait of ADHD might have been helpful in protecting our ancestors against livestock raids, thefts, and more. Essentially, the traits related with ADHD appear to help more with enhancing hunter-gatherer skills than those of a settler (Goldman et al., 2021).

Some ADHD symptoms still make adaptive sense today. For example, being vigilant or wary in the face of violence and prioritizing survival/safety over the higher executive functions like empathy, self-reflection, and emotion regulation. However, the social environment for children has changed significantly over the past century. Today there is a discrepancy between the strengths of children with ADHD (i.e., their tendency to explore, challenge, and try new ways of doing things) and schools. The traditional model of education where 20 or more students are taught in classrooms for 6 hours a day and 5 days a week runs counter to evolutionary strategies (Swanepoel et al., 2017).

Behavioral strategies in school should focus on allowing children with ADHD plenty of physical activity, encouraging fidget toys to when they have to sit still, making eye contact before giving instructions, and keeping instructions clear and simple. Adults with ADHD would benefit from understanding their evolutionary strengths and seek jobs where these are valued (Swanepoel et al., 2017).

Autism Spectrum

In ancient hunter-gatherer societies traits like repetitive behaviors, antisocial states, hyper-focusing on details, mechanical actions, and hyper/hypo sensitivity to stimuli found in autism spectrum disorder (ASD) would have benefited individuals. Hunters had to be able to identify and calculate the patterns of game movement through the seasons. They also had to tolerate isolation while hunting and make/invent tools (Dey et al., 2015). Gathers needed to be mindful of minute details in wild plants to differentiate between what is edible or poisonous. Hypersensitivity to environment would have been beneficial to noticing slight changes in the environment. Where hyposensitivity to temperature could allow people to endure extreme climates. In hunter-gatherer societies autistic traits may have allowed people to survive and provide for their community. Yet, these prehistoric traits may no longer offer the same benefits in the modern world (Dey et al., 2015).

Another evolutionary explanation for ASD focuses on the rapid evolution of human cognition. The AUTS2 gene has recently been linked to the origins of ASD. Precisely, the gene appears to play a role in the rapid evolution of human cognition. This suggests the same genes that may be beneficial in terms of cognition may also impact unfavorable traits of ASD. This theory indicates that ASD could be an evolutionary by product of the rapid evolution of human cognition (Dey et al., 2015). Some theories suggest that certain mutations in ASD genes may result in evolutionary advantageous trait such as higher intelligence among individuals with ASD when expressed under a specific genetic background (Tsur et al., 2016).

One study indicated that ASD genes are significantly longer than other brain-expressed genes, which are thought to be longer than other genes in the genome and their exome length is distinctive compared to other gene sets. It is not clear why the protein-coding sequence of ASD genes is unusually long. One potential reason is that it provides a large and adaptable target for genetic manipulations, which could contribute to the development of complex and diverse cognitive functions (Tsur et al., 2016). Evolutionary advantages and expansion of human cognition may correlate with the recent exponential technological growth as well as increased introverted characteristics.

Bipolar Disorder

From evolutionary perspective manic and depressive episodes of bipolar disorder resemble behaviors animals and humans use to communicate social status. For example, manic episodes demonstrated by high energy, fast/assertive speech, and extensive body posture could reflect the behavior that is triggered by winning dominance contests. While depressive episodes characterized by low motivation, lack of energy, and melancholic states could be translated as submissive behaviors observed in low-ranking individuals (Rantala et al., 2021).

Full-blown mania may not be adaptive, but hypomanic traits like creativity, inventiveness, cheerfulness, competitiveness, stimulus-seeking, and promiscuousness might have provided a reproductive advantage in our evolutionary history. It has also been suggested that mild versions of manic syndromes reflect fast life history strategies. One evolutionary explanation of depressive episodes proposes that depression could have evolved as an adaptation to climate, helping individuals save energy resources in winter and manic episodes were an adaptation to increase activities during spring and summer (Rantala et al., 2021).

Bipolar disorder is connected to the malfunctioning of the body's internal clock and sleep disturbances are typically caused by it. In the past researchers were unable to explain why people with bipolar disorder have a malfunctioning internal clock. However, it is now clear that the widespread adoption of electric light over the past century has created an artificial evolutionarily novel factor that distorts the boundary between the natural day/night cycle and causes circadian rhythm incongruities that occur in bipolar disorder which contributes to the mismatch between our evolutionary programing and current environments (Rantala et al., 2021).

The disruption of the internal clock causes symptoms of bipolar disorder because it interrupts the sleep/wake system. Internal clock desynchrony causes the pineal gland produce melatonin during the wrong time of the day or in excessive quantities. In a study, bipolar disorder patients in a manic phase were given 3mg of melatonin before going to sleep. The amount of sleep of the patients doubled and the symptoms of mania decreased. Lithium and valproic acid which commonly are used to treat bipolar disorder have also shown a stabilizing effect on the functioning of the internal clock. Since people with bipolar disorder are known to be sensitive to changes in circadian rhythm, an increase of natural light and the use of light therapy treatment can trigger a manic episode (Rantala et al., 2021).

The emergence of the evolutionarily novel conditions found in modern lifestyles cause neuroinflammation which triggers high risk/reward strategies that can lead to a dysfunctional manic state. In ancestral environments, the reward approach strategy may have remained at a hypomanic level as environmental factors that increase neuroinflammation were absent and depressive episodes might have remained at the level of an adaptive mood change without symptoms that occur in clinical major depressive episodes. Based on this new knowledge clinical bipolar disorder symptomology appears to reflect an acute manifestation of biobehavioral strategies expressed pathologically because of existing mismatched environmental conditions (Rantala et al., 2021).

There is evidence that suggests that multidimensional lifestyle interventions targeting diet, physical activity, self-motivation, and beliefs surrounding wellbeing are feasible and effective in treating bipolar disorder. Research suggests that people with bipolar disorder would benefit from having a regular rhythm of life (e.g., going to bed, waking up, and eating at the same time every day). Improved sleep hygiene (e.g., use of blackout curtains and avoiding electronic devices that emit blue light during the evenings) could help stabilize the circadian rhythm and improve treatment outcomes (Rantala et al., 2021).

Psychotic Disorders

Given the severe and debilitating nature of schizophrenia as we know it today, one would assume that there would be strong natural selection pressure eliminate the occurrence of the disorder in the population. It possible that schizophrenia is an extreme version of behaviors or cognitive processes that once offered an adaptive advantage. Recent studies support those lower levels of psychotic traits may have provided advantages that could explain the continued existence of psychotic disorders (Leathem, 2019).

Paranoia is one of the most recognized symptoms among schizophrenia patients. It is now suspected that paranoid thinking may have evolved as a sensitivity or alertness to social threat. Threats to prehistoric group unity possibly impacted the survival of individuals within the group. It would be advantageous for some members of groups to be suspicious of new members or outsiders (Leathem, 2019).

Other major symptoms of psychotic disorders include hallucinations. A recent study examined the perceptual abilities of non-clinical voice-hearers (NCVH). These individuals experience full auditory hallucinations but may not have other symptoms or functional impairments connected with a psychotic disorder diagnosis. The study enlisted NCVHs and non-voice hearing controls to do a noise detection task during an MRI scan. The noise detection task included listening to a series of white-noise clips and pressing a button if they heard distinctive noises in the clips. What the participants did not know was that 50% of the white-noise clips had recorded speech that had been acoustically reduced to a point that the speech was unintelligible (Leathem, 2019).

The study found that NCVHs were more likely than the control group to notice the existence of speech in the sound clips. They noticed it earlier than the controls and were more likely to remember specific words in the recordings. Group variations were seen in activation of the anterior cingulate cortex, a region in the brain correlated with the facilitation of attentional processes such as monitoring internal/external speech and sounds. The study demonstrated how processes in psychosis could have aided our evolutionary ancestors. Specifically, the bias for speech or significant sounds may have been advantageous in detecting threats from ambiguous sounds. The process may have also been beneficial during the early development of spoken communication and language (Leathem, 2019).

Another possible adaptation associated with psychotic disorders is creativity. The concept that madness accompanies genius dates back centuries. Evidence of link between creativity and psychosis is robust. Psychotic patients often perform better than controls on logic problems outside of practical limits. Additionally, schizotypal traits are associated with various measures of creativity from scientific tasks of divergent thinking to artistic success (Leathem, 2019).

Changing The Narrative

With the mounting evidence that the maladaptive features of mental disorders are the result of an evolutionary disconnect, clinicians can help patients cope by emphasizing how environments impact symptoms. Understanding mental health disorders as a biological variant that has adaptive value may help shift perceptions away from a disorder or disability to seeing someone who is stuck in an evolutionary mismatch.

References

Centers for Disease Control and Prevention. (2021, February 11). Stats of the state - suicide mortality. Link

Dey, S., Ding, T., Chang, J., & Nguyen, P. (2015). Evolution and autism | evolutionshorts. Link

Goldman, L., Robinson, D., & Krans, B. (2021). Did adhd help keep humans alive? Healthline. Link

Han, W., & Chen, B.-B. (2020). An evolutionary life history approach to understanding mental health. General Psychiatry, 33(6), e100113. Link

Leathem, L. (2019, February 14). Thinking about schizophrenia: Evolutionary explanations — psychology in action. Psychology In Action. Link

Rantala, M. J., Luoto, S., Borráz-León, J. I., & Krams, I. (2021). Bipolar disorder: An evolutionary psychoneuroimmunological approach. Neuroscience & Biobehavioral Reviews, 122,28-37. Link

Swanepoel, A., Music, G., Launer, J., & Reiss, M. J. (2017). How evolutionary thinking can help us to understand adhd. BJPsych Advances, 23(6), 410–418. Link

Tsur, E., Friger, M., & Menashe, I. (2016). The unique evolutionary signature of genes associated with autism spectrum disorder. Behavior Genetics, 46(6), 754–762.Link

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