A new analysis of soldiers attempting to join the U.S. Army Special Forces suggests that specific genetic variations play a role in how individuals handle extreme physical and mental pressure. The research identified distinct links between a soldier’s DNA and their cognitive performance, psychological resilience, and physiological stress response during a grueling selection course. These findings were published recently in the academic journal Physiology & Behavior.
To become a member of the elite Army Special Forces, a soldier must first pass the Special Forces Assessment and Selection course. This training program is widely recognized as one of the most difficult military evaluations in the world. Candidates must endure nearly three weeks of intense physical exertion. They face sleep deprivation and complex problem-solving exercises. The attrition rate is notoriously high. Approximately 70 percent of the soldiers who attempt the course fail to complete it. This environment creates a unique laboratory for scientists to study human endurance.
Researchers have sought to understand why some individuals thrive in these punishing environments while others struggle. Resilience is generally defined as the ability to adapt positively to adversity, trauma, or threats. It involves a combination of psychological stability and physiological recovery. While physical training and mental preparation are essential, biological factors also play a substantial role. Genetics help determine how the brain regulates chemicals and how the body processes stress hormones.
To investigate these biological underpinnings, a team of researchers led by Martha Petrovick of MIT Lincoln Laboratory and senior author Harris R. Lieberman from the U.S. Army Research Institute of Environmental Medicine launched a comprehensive study. Their goal was to determine if genetic profiles previously linked to mental health or stress responses in the general public would also manifest as resilience markers in elite soldiers. They hypothesized that specific genetic variations would correlate with success in the assessment course.
The study included 800 male soldiers who volunteered for the selection course. The participants were already active-duty soldiers who had completed other rigorous military training. They were young and physically fit, with an average age of 25. Before the assessment began, the researchers collected blood samples to analyze each soldier’s DNA. They specifically examined 47 different genes known to influence brain function, sleep cycles, and hormone regulation.
The researchers also administered a battery of standardized tests to the candidates. These assessments measured general intelligence and vocational aptitude. They also evaluated personality traits such as grit and self-reported resilience. The team collected additional blood samples to measure levels of cortisol and C-reactive protein. Cortisol is the primary hormone the body releases in response to stress. C-reactive protein is a biological marker that indicates inflammation and immune system activation.
The analysis revealed that several specific genetic variations were indeed associated with better cognitive performance and higher resilience scores. The researchers found that the influence of these genes often varied depending on the soldier’s ancestral background. This highlights the complexity of using genetic markers across diverse populations.
One of the key genes identified in the study was COMT. This gene provides instructions for making an enzyme that breaks down dopamine in the brain. Dopamine is a chemical messenger critical for motivation, executive function, and the ability to solve problems under duress. The researchers found that among White Hispanic candidates, specific variations of the COMT gene were linked to higher scores on intelligence tests. These variations are often referred to as the “warrior allele” in scientific literature because of their association with performance in competitive environments.
The study also highlighted the TPH2 gene. This gene is involved in producing serotonin, a neurotransmitter that helps regulate mood and emotion. Variations in this gene were associated with performance on non-verbal intelligence tasks among White Hispanic soldiers. The researchers observed that soldiers with two copies of a specific minor genetic variant performed better on these tasks than those with different genetic makeups.
The body’s internal clock also appeared to play a role in cognitive aptitude. The researchers examined PER3, a gene that helps regulate circadian rhythms and sleep-wake cycles. They found that certain variations in this gene correlated with scores on the Army’s vocational aptitude battery. This test helps the military assess a soldier’s potential for specific occupations. The link suggests that genetic factors influencing sleep patterns may also affect general cognitive abilities required for military tasks.
Beyond cognitive ability, the study examined genes linked to how individuals perceive their own ability to bounce back from stress. The researchers used a standardized survey called the Connor-Davidson Resilience Scale. In participants categorized in the “Other” demographic group, variations in the CRHR1 gene were associated with higher scores on this resilience questionnaire. The CRHR1 gene produces a receptor for a hormone that initiates the body’s stress response. This receptor is a key component of the hypothalamic-pituitary-adrenal axis, the system that controls reactions to stress and regulates digestion, the immune system, and mood.
Similar associations were found with the MAOB gene. This gene is responsible for an enzyme that breaks down several neurotransmitters, including dopamine and epinephrine. The study found that specific variations in MAOB were linked to higher self-reported resilience. This aligns with previous research suggesting that this gene plays a role in various aspects of mental health and the ability to recover from adverse events.
The researchers also looked for links between genetics and physiological markers of stress. They measured the concentration of cortisol in the soldiers’ blood. Cortisol levels typically rise during times of intense strain to help the body mobilize energy. However, chronic or poorly regulated cortisol can be detrimental. The study found that cortisol levels varied based on genetic profiles.
For Black participants, variations in the FKBP5 gene were linked to higher concentrations of cortisol. The FKBP5 gene acts as a regulator for the body’s stress receptors. It is part of a negative feedback loop that helps the body return to a normal state after a stressful event. Variations in this gene have previously been linked to depression and anxiety disorders in the general population. This study suggests that these same genetic mechanisms influence how healthy soldiers biologically respond to the extreme demands of Special Forces training.
Among White Hispanic soldiers, the CYP1A2 gene showed a similar relationship with cortisol levels. This gene encodes an enzyme in the liver that metabolizes various substances. It is perhaps best known for its role in breaking down caffeine and certain medications. The researchers found that soldiers with a specific variant of this gene had higher levels of circulating cortisol. This suggests a potential overlap between the biological pathways that process foreign substances and those that manage physiological stress.
It is important to note that while these genetic markers were associated with resilience traits, no single gene predicted whether a soldier would ultimately pass or fail the course. The researchers emphasized that resilience is a multifaceted trait. It is shaped by a complex combination of genetics, environmental factors, physical training, and psychological preparation.
The study also has limitations that must be considered. The participant pool consisted entirely of male soldiers. This means the findings may not apply to women or the broader civilian population. Additionally, the study was observational. It identified statistical links between genes and performance but cannot prove that these genes directly caused the differences. The associations were also specific to certain racial and ethnic groups, reinforcing the need for diversity in genetic research.
Despite these caveats, the findings offer a rare glimpse into the biology of human endurance. Most genetic studies on stress focus on individuals with psychiatric disorders or those who have experienced severe trauma. This research demonstrates that the same genetic factors are relevant in healthy, high-performing individuals. The genes that influence susceptibility to depression or anxiety also appear to shape the resilience phenotype under very difficult circumstances.
These findings suggest that the genetic basis for resilience is preserved even under the most severe conditions. Future research could explore how these genetic markers might be used to optimize training. Understanding these biological factors could eventually lead to new strategies to help individuals recover from extreme stress. This could have applications not just for the military, but for anyone facing challenging life experiences.
The study, “Genetic markers of stress, resilience and success at an elite military selection course,” was authored by Martha Petrovick, Jessie Hendricks, Emily K. Farina, Lauren A. Thompson, Joseph J. Knapik, Stefan M. Pasiakos, James P. McClung, and Harris R. Lieberman.
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