Michael Macy: Artificial worlds unlock secrets of human interaction

Macy

By Roger Segelken

What do flocks of birds, traffic jams, fads, drinking games, forest fires and residential segregation have in common? The answer could come from a new computational research method called agent-based modeling.

Michael Macy, a sociologist at Cornell, is using this powerful new tool to look for elementary principles of self-organization that might shed new light on long-standing puzzles about how humans interact. A professor and chair of Cornell's Department of Sociology, Macy spoke Feb. 14 at the annual meeting of the American Association for the Advancement of Science in Denver in a symposium, "Artificial Agent Societies: A Computational Future for the Social Sciences."

He began his lecture with a flock of computer-generated birds wheeling synchronously through aerobatic maneuvers. He credits Craig Reynolds, a pioneer of agent modeling and three-dimensional computer animation, for the 1987 discovery that the complex choreography of a flock requires that each bird (or "boid," as Reynolds called them) follows just three simple rules: head toward the center of your neighbors, match their speed and trajectory and avoid collisions. "Reynolds didn't model the flock as a unitary collective nor did he model isolated birds; he modeled their interactions at the relational level," Macy said. "That's agent-based modeling."

Traditionally, sociologists have tried to understand social life as a structured system of institutions and norms that shape individual behavior from the top down, Macy noted. In contrast, agent modelers suspect that much of social life emerges from the bottom up, more like improvisational jazz than a symphony.

In collaboration with his Cornell colleague David Strang, Macy has used agent-based models to study lemminglike fads among the corporate managers pilloried by Scott Adams in his "Dilbert" comic strip. Contrary to Adams' portrayals, top managers are highly intelligent and are paid huge salaries to get it right, Macy observed. The Cornell researchers' work, which won the theory prize from the Academy of Management, shows how fads that appear to reflect mindless conformity can be generated by the very opposite -- a single-minded preoccupation with performance and success.

Macy recently was awarded a grant from the National Science Foundation to tackle another familiar puzzle -- peer enforcement of norms that even the enforcers privately question. In collaboration with two Cornell graduate students, Robb Willer and Damon Centola, Macy is using an agent-based model to see how the diffusion and stability of unpopular norms might depend on the size and geometry of peer networks.

The father of teenagers, Macy ponders the curious appeal of self-destructive behaviors -- smoking, drinking, drug use, reckless driving, body-piercing and the like. For example, studies of college drinking find that students feel peer pressure to participate in drinking rituals that celebrate intoxication as a symbol of group identity.

"Yet it turns out that students' private beliefs deviate sharply from their perception of the social norm," Macy noted. "Contrary to campus legend, most students are actually uncomfortable about excessive drinking, at least when they are sober. They do not think drink
ing games are cool, but they think (incorrectly) that others believe this, and when they join in to secure social approval, their apparent enthusiasm reinforces the illusion that motivates the behavior in others."

When Macy's team tried to generate this dynamic on a computer, the agents always escaped the trap. But then the researchers remembered a lesson taught by Reynolds' "boids." "The boids only know about the behavior of their immediate neighbors, and that turns out to be the key to
the puzzle," Macy said. "Agents get trapped into enforcing a norm that most of them dislike when their normative expectations are mainly influenced by a small circle of friends."