Scientists sometimes struggle to understand why certain animals act as they do, especially social animals. A school of fish or a flock of birds, for example, behaves in many ways like a single creature. Yet exactly how the individuals organize themselves into a "superorganism" is still very much a mystery.

But believe it or not, these days insights into such self-organizing communities seem to come more often from computer hackers than from field biologists. Many programmers are creating on their desktops virtual environments populated with simulated animals. The nature of these artificial life-forms (or "a-life," for short) usually hinges on a special data string, which is analogous to the DNA blueprint of a living organism. This digital code defines how an a-organism interacts with its cybersurroundings and determines the likelihood that the simulated creature will reproduce.

Image Credit--DANIELS & DANIELS Although each virtual creature follows only a few simple rules, when a group of them encounters an obstacle (top), the individuals split up (center) and later rejoin (bottom), mimicking a flock of real birds.

To mimic real DNA, the cybercode is programmed to experience random mutations, which can alter the fitness of the artificial animal. So by tracking many generations of these byte-size beasties, you can in several minutes watch their digital DNA evolve in ways that might take nature millions of years to accomplish with a real genetic code. With much of this software available online (consult the premier a-life Web site, www.alife.org, or see www. aridolan.com/ad/adb/adib.html for an index of sites where you can download Java scripts), any interested amateur can now plumb the depths of evolution, at least in these virtual worlds.

If you take up this challenge, you'll be joining the ranks of people such as Craig Reynolds, now with Sony Computer Entertainment, who in 1986 developed an impressive model of flocking birds. Reynolds speculated that each bird in a flock acts on a simple set of directives. So he programmed his a-life creations, which he whimsically dubbed "boids," to follow just three rules. first, don't get too close to anything, including other boids. Second, try to match your velocity to that of the other boids around you. And third, always move toward the center of the pack of nearby boids.

The results of his simulation are remarkable. (Check out www.red3d.com/ cwr/boids/ for an eye-popping animation.) No matter how the boids are initially scattered, they quickly form a flock. When the group encounters an obstacle in cyberspace, it splits into two groups and reassembles on the far side.

Image Credit--DANIELS & DANIELS JAVA APPLET allows interested Web surfers to simulate carnivorous boids, called ¿floys¿.

Reynolds's boids seem to support the fascinating theory of emergent behavior, which describes how complex social interactions can arise when individuals obey a few rudimentary but very special rules. Reynolds's code contains no reference to flocking, much less any instructions for how a flock should navigate obstacles. And whereas most programs can't deal with situations that the programmer does not anticipate, in this simulation the boids execute a surprising array of sensible responses to unforeseen challenges. Reynolds remains a leading pioneer on the virtual frontier: his applications of computer animation to motion pictures won him an Academy Award in 1998.

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