In 2016, neuroscientists examined Alex Honnold’s brain in an fMRI scanner. Honnold climbs rock faces without a rope. If he falls, he dies. Researcher Jane Joseph showed him 200 fear-inducing, disturbing images. These stimuli activate the amygdala in normal people—the area of the brain that detects danger and sounds the alarm. In Honnold, nothing happened. Through years of exposure to real danger, his brain has learned to no longer process simulated threats as such. Honnold himself puts it this way: “There’s no adrenaline rush. If I feel one, something has gone terribly wrong.” It’s not as clear as it seems who the exception is in this story. Joseph’s findings suggest that Honnold’s brain functions exactly as a human brain should when it gets what it was built for. More risk makes him calmer, not less so. This raises an uncomfortable question: What happens to a person who lives in constant safety?

299,850 Years of Practice

Homo sapiens has existed for about 300,000 years. For 299,850 of those years, physical danger was not the exception: predators, hunger, tribal conflicts. Evolution shaped the human nervous system for precisely this environment. An organism whose stress response didn’t kick in immediately didn’t survive long enough to produce offspring. Evolutionary biologist Boyd Eaton wrote in 1988: “Genetically speaking, we are Stone Age people who have been transplanted into the present.”

Civilized humans today live more safely than any generation before them. The nervous system doesn’t know that. It keeps running, calibrated for lions that no longer attack, ready for dangers that are no longer there. The amygdala doesn’t interpret situations; it interprets signals: heart rate, cortisol, muscle tension. For millennia, these signals meant danger. Today, a deadline, a full inbox, or an unpleasant conversation trigger the same signals. The amygdala is doing its job: it sounds the alarm. The world around it has changed, but the system has not. A nervous system in a constant state of alarm, without ever having to cope with real danger—that has consequences.

Too little dopamine, too much everyday life

Not everyone reacts the same way to this constant alarm. Psychologist Marvin Zuckerman measured this in the 1960s: About ten percent of the population needs more—more stimulation, more intensity, more risk. They are disproportionately represented in emergency services, special forces, and on single-track trails. People with high sensation-seeking tendencies have measurably lower dopamine levels at rest. In everyday life, their system is active, but everyday stimuli aren’t enough to calm it down. Ashley Parr demonstrated this in a 2026 study: “Risk-taking behavior could be a way to kick-start the system when dopamine levels are too low at rest.”

Not every rider seeks thrills for their own sake. Some need it because their dopamine system receives too little stimulation in everyday life. The amygdala fires anyway—in response to deadlines, conflicts, or even meaningless noise. Risk is a basic biological need, just like sleep, exercise, and social bonding. Those who consistently avoid this stimulus pay a price.

When the amygdala fires in response to a lion, action follows: flight or fight—the body discharges its energy. That’s how it was for 300,000 years. Today, the alarm goes off, but the discharge doesn’t happen. The body remains in a state of emergency: cortisol in the blood, muscles tense, heart rate elevated. People with high sensation-seeking tendencies who can’t find balance compensate through substance abuse, risky driving, or criminal behavior. The same nervous system that drives some people toward extreme sports finds its way out, whether constructively or not. The drive is identical; the outlet is different. 

When the brain stops ruminating

In 2012, researchers led by Billy Sperlich studied elite downhill riders before their races. Cortisol levels were twice as high as at rest; the body is preparing: Adrenaline constricts the pupils, draws blood to the extremities, and sharpens the senses. Cortisol makes the brain hypersensitive. The release follows as soon as the rider starts riding. At that moment, the brain does something unexpected: the default mode network shuts down. That part of the brain that never stops in everyday life—brooding, anxiety about the future, inner monologue. At 50 kilometers per hour between trees, there’s no capacity left for that. Monday’s deadline no longer exists, nor does the packed calendar. All that remains is the line ahead of him. The mountain biker is in the flow.

Every mountain biker knows this stillness after the descent. The mind is empty, the body exhausted—no brooding, no inner noise. For a few minutes, the nervous system is where it has belonged for 300,000 years. Perhaps that is the real question—not whether a life is safe enough, but whether it is alive enough.