Our Brain Responds to City Noise as if Under a Predator Attack

Over millennia, the human brain has learned to detect danger signals around it. A noise in the leaves, a low rumble or a shape between the trees was enough. This immediately triggered intense vigilance, which disappeared as soon as the threat seemed to have passed. Today, predators have disappeared from cities, but noise, density and incessant stimulation continue to activate the same defense circuits. It is in this confusion between reality and perception that chronic stress sets in, day after day.

An archaic alert designed to survive, not endure

For most of human history, stress was rare and occasional. It prepared the body to flee or defend itself in the face of real danger. In natural environments, the sound of wind, insects or wild animals did not trigger lasting physiological distress. According to ScienceAlert, our nervous system was calibrated to react to a direct threat like a lion, then return to balance once the danger has passed.
Journalist Barbara Simpson, from the University of Zurich, recounts an experiment carried out in the forest, where participants, after just a few hours in contact with the trees, felt a measurable drop in their heart rate, emotional calming and a reduction in stress markers.

In a study published in the journal Biological Reviews, anthropologists Daniel Longman and Colin Shaw explain that our biological adaptation was built in environments rich in vegetation, natural light and low human density. They emphasize that the rapid transformation of habitats caused by industrialization is creating an unprecedented environmental disruption. According to them, cities concentrate stress factors such as noise, air pollution, night light or microplastics, and these factors disrupt hormonal and immune regulation.

Living in the city continually triggers chronic stress

Chronic stress appears when ancestral mechanisms of vigilance are triggered too often, without returning to balance. Our body reacts as if we are constantly confronting predators, with a continuous influx of adrenaline and cortisol, but without any recovery phase. Experiments conducted by the Human Evolutionary EcoPhysiology group at the University of Zurich show that participants exposed to a noisy urban environment had higher blood pressure, faster breathing and impaired immune responses, even in the absence of real danger. The researchers measured these effects after just three hours of exposure.

Longman and Shaw highlight that industrialization introduced biological pressures that could alter fertility, cognition, immunity, and fitness. They explain that noise and light pollution disrupts sleep, that contaminated air affects the brain and that the absence of natural microbiota weakens immune regulation. According to them, the accumulation of these factors triggers a prolonged state of vigilance, characteristic of chronic stress.

Should we rethink urban planning as a public health issue?

Researchers do not seek to revive the past. Rather, they propose to reconnect our body to its environment. Vegetation promotes the production of immune cells. It also helps regulate the heart rate and concentrate better. Even simple images of nature are enough to lower cortisol levels.

According to them, nature can no longer be considered a luxury, but an indispensable component of human health. They invite decision-makers to integrate physiological data into urban planning and to design cities that respect the biological limits of the human body. They imagine urban spaces where greenery is not limited to isolated parks, but is included in schools, hospitals, offices and transport. A city that soothes instead of keeping the body in permanent vigilance. A city where our nervous system would no longer seek to flee every noise as if it announced a vital danger.