Fly moves: insects buzz about in organized abandon.

Flies aren't deep thinkers. Yet these humble creatures display a penchant for spontaneous behavior that represents an evolutionary building block of voluntary choice, also known as free will, a controversial new study suggests.

By mathematically analyzing flight maneuvers, a team of scientists showed for the first time that fruit flies move in a way that is neither wholly random nor predetermined. An evolved brain mechanism in the fly must generate spontaneous, unpredictable flight shifts to aid in vital tasks such as avoiding predators and tracking potential mates, conclude neuroscientist Bjorn Brembs of the Free University of Berlin and his colleagues.

"Our results provide strong evidence that the exact prediction of an individual [fly]'s behavior is impossible," Brembs says. This finding dovetails with other evidence that people must have a neural ability to generate spontaneous behavior. Without such an ability, "it's hard to imagine people having access to free will," he adds.

The researchers reject the traditional assumption that flies and other animals search for food and engage in other critical behaviors primarily by using their senses to glean clues from their surroundings. Instead, the new results suggest that circuitous foraging routes and other behavioral signatures of flies arise spontaneously, although sensory clues may also play a role. Brembs' team describes its findings in the May PLoS ONE.

The researchers placed a drop of glue between the head and thorax of a fly to attach it to a hook inside an experimental chamber. Each of the 13 flies tethered in this way could still beat its wings and move its body. Uniformly white surroundings offered no visual feedback to the animal. A special device recorded the timing and magnitude of each fly's movements.

In this barren environment, the flies rarely stayed still and frequently changed direction. Mathematical methods developed by study coauthors George Sugihara and Chih-hao Hsieh, both of the University of California, San Diego, indicated that flies' spontaneous flight maneuvers were neither totally random nor completely regular or repetitive. Instead, they had a structured variability that mathematicians describe as fractal order.

Brembs plans to identify brain areas responsible for flies' spontaneous movements.

At least part of the so-called default network in people's brains generates spontaneous behavior according to rules similar to those operating in flies, Brembs speculates. The default network exhibits spontaneous activity in people at rest (SN: 5/5/07, p. 276).

Neuroscientist Randolf Menzel, a bee researcher also based at the Free University of Berlin, suspects that the brain stimulates spontaneous behavior in flies and other insects as one way of producing decision options from which the animal automatically makes a choice. Brembs' results bear no relation to the concept of free will, Menzel holds.

Psychologist David L. Gilden of the University of Texas at Austin also sees no reason to connect Brembs' results to free will. Flies' spontaneous behavior resembles the fractal structure of many biological and physical systems poised between stability and chaos, Gilden notes. These systems include traffic flow, quasar emissions, and people's memory for time and spatial intervals.

Fractal organization endows a system with the flexibility to change and adapt to new circumstances, Gilden theorizes. "This issue goes way beyond biology,' he says.