Mark Pagel

“One of the earliest and most pleasing demonstrations of complex behaviors emerging from agents following local rules was Craig Reynolds’s simulation of the motions of flocks of birds as they fly around in the evening sky feeding on insects. The fluid and flowing motions of these flocks wheeling around the sky, sometimes separating and then coming back together, avoiding collisions with each other, looks to be a supreme act of purposeful cooperation on the wing. But Reynolds achieved a surprisingly realistic simulation by assigning the individual birds just three simple rules: one is to stay near to and steer in the same direction as your nearest neighbor; the second is to follow the main heading of the group; and the third is to avoid crowding. Add to these rules a small amount of randomness to individuals’ behaviors, and flocks of “boids,” as Reynolds called them, elegantly and sublimely fly around computer screens. No one bird is directing the flock and the birds are not actively cooperating to produce it. It emerges from the simple rules.”
― Mark Pagel, Wired for Culture: Origins of the Human Social Mind