The Evolution of Modern Anxiety: Why our Brain Fears Uncertainty

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Written by Alex Bergholt ‘27

Edited by Andrew Ni ‘26

We live in an age defined by uncertainty. From political instability to climate change to the constant stream of breaking news, it can feel like the world is spinning faster than we can keep up.  It seems that all we have to do is turn on the radio to be blasted by a slew of unknowns. However, this constant unpredictability doesn’t just shape our society, it directly affects our biology. Science shows that even mild anxiety can activate the same brain circuits that respond to fear. In fact, our brain is hardwired to treat uncertainty as a threat to our survival.  

At the center of this response is a small, almond-shaped body located deep in the temporal lobes of the brain. It plays a key role in processing emotions, and it is the alarm system that detects danger and triggers our fight-or-flight reaction. When a threatening stimulus is perceived by the brain, the amygdala identifies this stimulus and initiates a physical and physiological cascade [2]. Evolutionarily, it made sense for the brain to develop such a programmed physiological response to uncertainty. However, as our environment has rapidly changed, our own wiring and biology hasn’t, and such a response now fuels our modern day anxiety.

A recent study by Herry et al. (2007) investigated this phenomenon, whether unpredictability itself, without any associated threat or reward, was enough to activate the amygdala and induce anxiety-like behavior in both mice and humans [2]. In the study, when the mice were exposed to temporal unpredictability using a series of sound pulses in an otherwise neutral sensory environment, the researchers found that unpredictable sound pulses increased the expression of the gene c-fos and prevented rapid habituation of single neuron activity in the basolateral amygdala. For context, c-fos is a gene that gets “turned on” in active neurons, a “neural activity marker,” per se. As neurons fire, c-fos levels rise. Thus, increased gene expression of c-fos in the amygdala indicated strong neuronal activation due to these unpredictable sounds. “Rapid habituation” occurs when neurons are exposed to the same stimulus over and over, and refers to their weakened response over this duration. In this case, however, the neurons within the basolateral amygdala did not habituate, and continued to fire strongly. This indicates that unpredictability blocks the brain’s ability to, in essence, calm down. In other words, unpredictable, but not predictable, auditory stimulation induced avoidance and anxiety-like behavior in the mice. When tested on humans, the same pattern emerged with temporal unpredictability also causing sustained neural activity in the amygdala and similar anxiety-like behaviors [3].

But why are we wired this way? To begin, we must understand how the brain processes fear and the physiological responses it elicits. At the onset of a stressful event, the amygdala sends a distress signal to the hypothalamus, which functions like a command center. The hypothalamus communicates with the rest of the body through the nervous system, activating both sympathetic and parasympathetic responses [4]. In this case, after the stress signal arrives from the amygdala, the hypothalamus activates the sympathetic response. Signals are relayed to the adrenal glands, which pump the hormone epinephrine into the bloodstream [4].

This epinephrine, or adrenaline as you may have heard it referred to, elicits a series of physiological responses so that the body can react adequately to the perceived stimulus. The heart beats faster, pushing more blood to the muscles, heart, and other vital organs; pulse rate and blood pressure increase, as does breath rate; and, finally as the initial surge of epinephrine subsides, the hypothalamus activates the second component of the stress response system: the HPA axis. This axis keeps the sympathetic nervous system, the “gas pedal”, pressed down. A variety of cascades prompt the release of cortisol from the adrenal glands keeping the body “revved up” and on high alert. Only when the perceived threat passes, cortisol levels fall and the parasympathetic nervous system dampens the stress response [4].

Evolutionarily, it makes sense why we are wired this way, and why our body elicits such a large response to uncertainty or fear. To ensure our safety, our brain functions as a “prediction machine,” constantly on the lookout for patterns in order to anticipate events. If you were a caveman picking berries and you heard an unordinary rustle in the bushes, it paid off to activate your fear response. Yes that rustling could’ve just been the wind, but it also could’ve been a saber-toothed tiger [5]. Shift to modern times, however, and the math is not so simple. Whether it be a grade uploaded to Canvas from a professor, an update regarding polls for the upcoming election, or a text from an ex, we seem to be constantly “under threat.” This activates the same biological mechanism as a predator did years ago, but now there is no need for such a response. Instead, we inadvertently become stuck in a hypervigilant state, and our nervous systems are running on fumes. In cases of chronic anxiety, the amygdala may be overactive, or its threat assessment system may become dysregulated.

Awareness, however, could prove to be an antidote. In fact, one study found that when people are exposed to fear signals they can’t consciously perceive, the amygdala response is stronger and longer-lasting than when they consciously perceive said signal [5]. In other words, when we bring the unconscious into consciousness, our amygdala quiets down, allowing the more rational part of our brain to take over. In a world that thrives on uncertainty, we can’t control every variable. But since you’ve already read this article, maybe the next time uncertainty hits, you’ll remember, it’s just your brain trying to keep you safe.

References:

1. University of California, Davis Health. “The Roots of Fear: Understanding the Amygdala.” October 1, 2024. https://health.ucdavis.edu/news/headlines/the-roots-of-fear-understanding-the-amygdala/2024/10

2. Herry, Cyril, et al. “Processing of Temporal Unpredictability in Human and Animal Amygdala.” The Journal of Neuroscience : The Official Journal of the Society for Neuroscience, U.S. National Library of Medicine, 30 May 2007, pmc.ncbi.nlm.nih.gov/articles/PMC6672268/ 

3. Professional, Cleveland Clinic medical. “The Amygdala: A Small Part of Your Brain’s Biggest

4. Dharma Lab, et al. “Fear, Uncertainty, and the Narrowing of the Mind.” Fear, Uncertainty, and the Narrowing of the Mind, Dharma Lab, 10 Sept. 2025, dharmalabco.substack.com/p/fear-uncertainty-and-the-narrowing. 

5. Dharma Lab, et al. “Fear, Uncertainty, and the Narrowing of the Mind.” Fear, Uncertainty, and the Narrowing of the Mind, Dharma Lab, 10 Sept. 2025, dharmalabco.substack.com/p/fear-uncertainty-and-the-narrowing. 

6. Abilities.”  Cleveland Clinic, 19 Mar. 2025, my.clevelandclinic.org/health/body/24894-amygdala. 

7. “Understanding the Stress Response.” Harvard Health, 3 Apr. 2024, www.health.harvard.edu/staying-healthy/understanding-the-stress-response.