Books, movies and hiker-lore all predict that, unaided by landmarks or celestial objects, people tend to walk in circles. But few have tested whether this happens and, if so, why.
Jan Souman at the Max Planck Institute for Biological Cybernetics in Tübingen, Germany, and his team tracked people's movement through unfamiliar terrains — Bienwald Forest in Germany and the Tunisian Sahara Desert — using the Global Positioning System.
During outings on cloudy days (blue trails pictured in inset), and one on a moonless night, subjects tended to walk in loose, meandering circles, which suggests that external information is key to maintaining course. Blindfolded walkers often veered into tighter circles of less than 20 metres in diameter.
Common explanations for circular walking invoke physiology — handedness or body asymmetries, for example. But the authors found little evidence that people turn consistently in one direction, suggesting a more random process.