# Why Humans Walk in Circles: The 2009 Max Planck Test

*Science & Technology · Priya Nair · 2026-08-17*

## TL;DR

In 2009, researchers at the Max Planck Institute for Biological Cybernetics in Germany tested why humans walk in circles without visual references. Using GPS tracking in the Sahara Desert and a German forest, they found that random sensory noise, not leg dominance, causes curved walking paths. The results pointed away from the long-held strong leg theory.

## Key facts

- The 2009 experiment took place in the Sahara Desert in southern Tunisia and the Bienwald Forest in southwestern Germany, where participants walked while GPS devices tracked their paths.
- When the sun or moon was visible, participants generally maintained their direction, but cloudy skies sent their routes curving.
- Blindfolded participants veered off course almost immediately, with some tracing circles with diameters smaller than 20 meters.
- The researchers found no consistent left or right turning bias, which pointed away from the "strong leg" theory as the primary cause.
- Instead, the study pointed to small uncertainties in the brain's direction-calculating system as the reason for circular walking patterns.

## The Desert Scene We All Know Too Well

You have seen it in a dozen films: a group of lost travelers trudges through the desert or a dense forest for hours, only to realize they have walked right back to the spot where they started. It feels like a screenwriter's trick, a cheap way to build tension. But here is the thing. It is not fiction. Without reliable visual cues, human beings genuinely wander in circles, often without noticing until they cross their own footprints.

You can test this yourself right now. Close your eyes and try to walk in a perfectly straight line across a room. For the first few steps, you will hold your direction. Then, almost imperceptibly, you drift. Maybe to the right, maybe to the left. The longer you walk, the more pronounced the curve becomes. The same thing happens in a blizzard, in thick fog, or in total darkness, whenever your brain loses its fixed reference points.

The question is why. For years, the popular explanation pointed at our bodies. The theory went that one leg is slightly stronger or a touch longer than the other, and that small asymmetry nudges us in the same direction with every step. Over time, those tiny deviations pile up into a wide arc. It sounded reasonable enough. But it had a fatal flaw: people do not always turn the same way. The same person might circle left on one attempt and right on the next, which a purely physical explanation cannot account for.

Researchers at the Max Planck Institute for Biological Cybernetics in Tübingen, Germany, decided to put this to a real test in 2009. They sent volunteers out into two very different landscapes: the vast, empty stretches of the Sahara Desert in southern Tunisia and the dense, flat Bienwald Forest in southwestern Germany. Every route was tracked with GPS devices. When the sun or the moon hung clearly in the sky, the walkers mostly held their line. But once clouds swallowed those celestial markers, their paths began to curl. Some participants crossed their own tracks repeatedly without ever realizing it.

Blindfolded participants fared even worse, veering off course almost immediately. According to the study, some drew circles with diameters smaller than 20 meters. And crucially, the same individual did not always bend to the same side. That inconsistency pointed away from leg length or strength as the culprit. The real story lives in how the brain pieces together information from the inner ear, the muscles, and the joints when the eyes have nothing steady to lock onto. Each step introduces a small, random error in our sense of direction. With no visual anchor to correct it, the brain quietly accepts the wrong heading as straight ahead. Error builds on error, and the path bends into a loop. That is why humans walk in circles: not because of a single physical quirk, but because our internal compass is just a little bit fuzzy, and without a fixed point to reset it, the drift takes over.

## The 'Strong Leg' Theory That Made Sense (But Was Wrong)

For decades, the go-to explanation for why humans walk in circles was body asymmetry. The logic went like this: one of your legs is slightly stronger or a touch longer than the other, so every step you take nudges you a little in the same direction. Those tiny nudges pile up over hundreds of steps, and before you know it, you have traced a wide, looping circle back toward where you started.

It sounded perfectly reasonable. If your right leg is half a centimeter longer, of course you would drift left with every stride. But there was a glaring problem with the theory that anyone could spot: people do not always drift the same way. The same person might veer right on one walk and left on the next. Leg physics alone could not account for that inconsistency, which meant the real answer had to live somewhere else in the body.

That puzzle is exactly what researchers at the Max Planck Institute for Biological Cybernetics in Tübingen, Germany, set out to solve in 2009. They took volunteers out into two very different landscapes: the vast emptiness of the Sahara Desert in southern Tunisia, and the dense, flat Bienwald Forest in southwestern Germany. Each walker carried a GPS device that recorded their route with precision, so the scientists could later map every twist and turn they made.

The results were striking. When the sun or moon was clearly visible, participants held a straight line without much trouble. But once clouds swallowed the sky or no reliable landmark remained, their paths began to curve. Some people crossed their own tracks multiple times without ever noticing. The most telling detail came from blindfolded walkers, who lost their way almost immediately. Some traced circles with diameters smaller than 20 meters. And crucially, the same person did not always bend to the same side. One trial might send them curving right, the next left, which pointed away from the idea that a fixed physical quirk in their legs was driving the behavior.

So if not the legs, then what? The answer, it turns out, is far more interesting than a simple anatomical flaw. Walking straight is not just about putting one foot in front of the other. It is a constant conversation between your eyes, your inner ear, and the muscles and joints throughout your body, all working together to keep you oriented. When those systems lose their reference points, the whole process falls apart in a way that has nothing to do with how strong your left leg happens to be.

## The 2009 Max Planck Experiment That Settled It

In 2009, researchers at the Max Planck Institute for Biological Cybernetics in Tübingen, Germany, decided to test why humans walk in circles when they lose their bearings. They took volunteers out into two very different landscapes: the vast emptiness of the Sahara Desert in southern Tunisia and the dense, flat Bienwald Forest in southwestern Germany. Every walking route was tracked with GPS devices, giving the team hard data on how people actually move when no obvious landmarks exist.

The results were striking. When the sun or moon hung clearly in the sky, participants mostly held their course with little drift. But when clouds swallowed those celestial cues, something shifted. Routes began to curve. Some walkers crossed their own paths several times without ever realizing it, convinced they were moving in a straight line the whole while.

The blindfolded participants showed the effect even faster. Deprived of sight entirely, they drifted much more quickly, and some traced circles with diameters smaller than 20 meters. That made the finding even more striking. It was a tight spiral that formed quickly, not a slow arc that took dozens of steps to appear.

Here is the detail that pointed away from the old explanation. The same person did not always veer to the same side. One trial might bend a walker to the right, the next to the left. If a strong or long leg were the culprit, the turn should have been consistent every single time. It was not. That inconsistency pointed somewhere else entirely: the brain, not the body, was making the error.

## Why Walking Straight Is Harder Than It Looks

Walking straight is not simply putting one foot in front of the other. Your brain is constantly juggling information from several sources at once: your eyes lock onto fixed points in the environment, your inner ear reports on head movement and balance, and your muscles and joints send signals about where your body is in space. When all those systems agree, you move in a clean line without thinking about it. Take away just one piece of that puzzle, and the whole system starts to wobble.

Think about what happens when you close your eyes and try to walk across an empty room. For the first few steps, you manage fine. But the longer you go without a visual anchor, the more your path drifts. A building, a tree, a mountain, a star, or the sun gives your brain something to measure against. With a fixed reference point in view, you notice small changes in direction and correct them almost instantly.

Without those visual cues, you are left relying only on your inner ear and the feedback from your muscles and joints. Those systems are effective, but they are far from perfect. Every single step introduces a tiny, random error in your sense of direction. On its own, each error is too small to notice. But errors accumulate. When your eyes cannot catch and fix them, your brain eventually accepts the wrong direction as the new "straight ahead." You think you are walking in a line, but you are actually curving, step by invisible step.

That is why people do not trace perfect geometric circles when they wander. The paths are irregular, winding, and they loop back on themselves in unpredictable ways. Circular walking is the result of small uncertainties in our direction-calculating system, not one fixed physical flaw. It is a quirk of how our brains piece together imperfect information, and it explains a lot about why humans walk in circles when the world around them offers no steady point to hold onto.


## Frequently asked questions

**Why do humans walk in circles when there are no visual cues?**

Without fixed reference points, tiny random errors in our sensory systems build up over time, and the brain simply accepts the wrong direction as "straight ahead." Each small mistake compounds on the last, gradually bending the path into a curve. This is the core reason why humans walk in circles when visual landmarks disappear.

**What was the strong leg theory of walking in circles?**

For years, scientists believed that one leg being slightly stronger or longer than the other caused consistent drift in one direction. The logic seemed sound, but the theory fell apart because people don't always turn the same way. A person might curve left on one attempt and right on the next, which physical leg differences alone cannot explain.

**How did the 2009 Max Planck Institute experiment test walking in circles?**

Researchers at the Max Planck Institute for Biological Cybernetics in Tübingen, Germany, ran field experiments in 2009 with volunteers walking in two very different landscapes: the Sahara Desert in southern Tunisia and the Bienwald Forest in southwestern Germany. Every route was tracked with GPS devices. When the sun or moon stayed visible, participants held their course. When clouds hid those celestial cues, their paths began to bend.

**Why do blindfolded people walk in circles faster than sighted people?**

Without any visual reference at all, sensory errors pile up much more quickly. In the Max Planck experiments, blindfolded participants curved into circles with diameters smaller than 20 meters. Interestingly, the same person did not always drift to the same side, showing that the wandering is not caused by a fixed physical quirk.

**Where did the Max Planck researchers conduct their walking experiments?**

The 2009 study took place in two deliberately remote locations: the vast Sahara Desert in southern Tunisia and the dense, flat Bienwald Forest in southwestern Germany. Both settings offered few or no stable visual landmarks, making them ideal natural laboratories for testing how humans navigate without visual guidance.

**What causes the small errors that make us curve while walking?**

Our inner ear sends balance signals, and our muscles and joints constantly report body position, but these systems are not perfect. Every step carries a slight, random error in our sense of direction. Normally, the eyes catch and correct these mistakes. When visual cues vanish, those tiny inaccuracies go unchecked and accumulate into a noticeable curve.

**Can people walk in a perfectly straight line with their eyes closed?**

Only for a handful of steps. Close your eyes and try it; you might stay straight for a few paces, but drift begins almost immediately. Without visual input to reset the brain's internal compass, the path quickly becomes an arc. The longer you walk blind, the tighter and more irregular that arc tends to get.

**Why do people in deserts or forests often end up where they started?**

When no fixed visual references exist, accumulated errors bend the walking path into a loop. The brain keeps updating its idea of "straight" based on faulty data, so the route curves and eventually circles back on itself. That is why lost hikers in featureless terrain sometimes cross their own tracks without ever realizing it. Editorial note: Any details about the study's exact sample size or specific participant outcomes that remain unconfirmed are presented as such, with the core findings based on the published research.

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