In 2 million BCE, a Paleolithic hunter-gatherer searched for food in the African savannah. In a moment, something feels wrong to her. Her muscles stiffen, her heart rate increases, and she goes silent. Her eyes scan the tall grass, looking for the slightest movement. She spots the tiger crouching in hiding and enters fight or flight. She dashes back to the safety of the pack. In 2024 AD, her descendent pours over his emails, convinced his coworkers to hate him. Like her, he’s frozen. His muscles are tight and his heart is pounding. He continues to scan his email inbox, looking for danger. Through the evolution of anxiety, that same impulse that kept his ancestor alive is the one threatening his job performance.
Evolution of Anxiety
In both of the above examples, the humans in question have experienced a release of adrenaline. Adrenaline is a hormone the body releases when we perceive danger. One can think of adrenaline as granting very modest superpowers. Your heart beats faster, pushing more blood to the muscles and brain, giving a boost in strength and alertness. Your breathing rate increases, delivering more oxygen throughout the body. You begin to sweat, which cools the body in case it needs to begin running or fighting. Your pain tolerance increases. Energy spent on temporarily non-essential activities like digestion is suppressed. In such a moment, the body becomes most capable of engaging in fight or flight. These effects make up what we know to be the symptoms of anxiety.
Understanding these effects of adrenaline may allow us to understand the evolution of anxiety. The foundation of evolution is natural selection, in which those best suited for their environment survive and pass on their genes, while those less suited die more frequently and fail to reproduce. Early humans that had strong adrenal responses could run faster and fight harder than those that didn’t, and would ultimately survive more encounters. However, this account only accounts for the fear response, which is distinct from anxiety. Anxiety is attuned to the possibility of future threats.
Take our hunter-gatherer from earlier for example. She did not have to wait for the tiger to jump out before her adrenal response began. She was already primed to be vigilant and speedy. Evolutionary anxiety also helped guide decision-making. An early human that had less attunement to future risk may waltz into a cave or happily take a bite out of an unidentified mushroom. These humans did not survive as well as those who exercised higher degrees of anxious caution.
Anxiety in the Modern World
Fortunately, most humans no longer exist in the eat-or-be-eaten world of the hunter-gatherer. The comforts of modern industrial society have significantly lowered our exposure to predation. This development, one that has taken several millennia, is a minuscule amount of time from an evolutionary standpoint. Our brains are still wired to the lifestyle of our paleolithic ancestors, which creates a disconnect between how our brains have evolved to behave and the conditions in which we live. Essentially, society developed faster than our brains could evolve. As a result, we are still primed for fight or flight danger in a world where such an impulse is not only unnecessary but oftentimes counterproductive.
Take the examples of the hunter-gatherer and office worker given earlier. The office worker is experiencing the same adrenal response as his ancestor, the very adrenal response that saved her life and allowed her to pass on her genes to him. However, no tiger is hiding in his office. His brain is forced to search for the source of this anxiety or to invent reasons. The adrenal effect we know to be anxiety symptoms, which were meant to keep him alive in the presence of danger, can only get in the way of his job performance. The conditions which once made anxiety favorable can now render anxiety counterproductive and harmful.
Neuroplasticity and Anxiety Treatment
So where does that leave us? Are those of us with overactive fight-or-flight adrenal responses doomed to permanently suffer with a biologically outdated brain, one ill-suited for the comforts and challenges of modern life? Fortunately, the same environmental context that gave rise to anxiety also allowed the mechanism by which we can teach our brains to understand when we are safe.
Imagine our hunter-gatherer who comes across a strange mushroom and wisely feels anxious about the prospect of eating it. Food is scarce, so she takes a minuscule bite and waits a day. She feels fine and takes a slightly larger bite the next day. Slowly she eats more until she recognizes the mushroom is edible and she now has a dependable source of food. Just as her anxiety was evolutionarily protective, so was her brain’s ability to adapt to new information. It lessened anxiety around known safe situations. This ability for the brain to adapt to new information and experiences is known as neuroplasticity, which is foundational in humans’ evolved ability to think consciously and plan.
This evolved capacity for the brain to alter its fight or flight response as the result of new experiences is the mechanism by which we can treat anxiety. Exposure therapy, in which one exposes oneself gradually to the source of their anxiety, works with this dynamic. As catastrophe fails to manifest in the presence of the anxiety source, the brain rewires to view the situation as safe. Other means of treatment, such as cognitive reframing or grounding oneself in the reality of the situation, also serve to provide new information and experiences for the brain to adjust to and alleviate the adrenal response.
Our office worker, for example, may avoid interacting with his coworkers as it causes him anxiety. If he gradually exposes himself to interaction with them and experiences that his perceived threats do not come true, his brain will gradually mitigate his anxious thoughts and feelings. His brain comes to understand that there is no tiger present, and adrenal fight or flight preparations are not necessary.
Rewiring Anxiety for Today
While anxiety may have once been an adaptive response that helped our ancestors survive in a world full of predators and other threats, the same biological mechanisms can sometimes hinder our well-being in the modern world. The disconnect between our evolved responses and contemporary life means that our brains can overreact to situations that no longer carry the same dangers. However, thanks to evolved neuroplasticity, we can reshape our responses over time. By gradually confronting our anxieties and challenging our brain’s outdated survival instincts, we can rewire our thought patterns and diminish the fight-or-flight response, allowing us to navigate the complexities of modern life. The same capacity that once helped us survive in the face of real danger can now help us adapt to the challenges of a world where tigers are no longer lurking in the grass, but new anxieties still arise.
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Have you found yourself experiencing fight or flight from everyday circumstances in modern life? How have you coped with this evolutionary response? Join the conversation in the comments below!
- The Evolution of Anxiety: How 2 Million Years Shaped Your Mind - March 26, 2025
