All together now
It is not only the scientific literature that documents the unexpected "doughnut" pattern in swarms ("The Mind of the Swarm," SN: 11/25/06, p. 347). Italo Calvino's fictional Mr. Palomar observed (rather more lyrically) about the flocking of Roman starlings, "Finally a form emerges from the confused flutter of wings, advances, condenses: it is a circular shape, like a sphere, a bubble, the balloon-speech of someone who is thinking of a sky full of birds ... " (Mr. Palomar, 1985, Harcourt Brace).
The article argues that reaching a consensus for movement is more complicated in humans than in animals, requiring "fancy cognitive skills." However, in an airport or on a busy sidewalk, simple rules linked to crowd density and speed of walking may emerge to influence behavior in a rather mindless way.