It’s hard to imagine getting two-dozen strangers to agree on almost anything. But in a study by Penn’s Damon Centola, groups of 24 people reliably came to consensus, provided the interactions between them were structured just so.

Centola, an associate professor in the Annenberg School for Communication and the School of Engineering and Applied Science and director of the Network Dynamics Group, is interested in how behaviors and ideas spread through social networks.

In a study published in the journal Proceedings of the National Academy of Sciences, he partnered with physicist Andrea Baronchelli, an assistant professor at City University London, to design an online experiment, dubbed the “Name Game,” that would track how the structure of a social network might influence how and whether a population came to agreement.

The researchers recruited participants online and grouped them in games of 24 players each. Each player was assigned a particular position within an online “social network,” though they weren’t aware of their position or even how many other players were in the game.

In each round of the game, participants were paired, shown a photograph of a human face, and asked to give it a name. If both players provided the same name, they won a small amount of money. If they failed, they lost a small amount and saw their partner’s name suggestion. The game continued with new partners for as many as 40 rounds.

The researchers tested three different network structures. In two of the networks, players repeatedly interacted with the same four partners. These groups never reached agreement on a single name.

But in the third network, in which participants partnered with a player selected at random from around the network in each new round, the result was different.

“Consensus spontaneously emerged from nothing,” Centola says. “At first it was chaos—everyone was saying different things and no one could coordinate—and then all of a sudden people who had never interacted with each other were all using the same words.”

The researchers found that the results scaled up, with games of 48 or even 96 players reaching consensus spontaneously. Centola says these findings help explain how social conventions can take hold in populations, even in those as large as a nation.

“Our study explains how certain ideas and behaviors can gain a foothold and, all of a sudden, emerge as big winners,” Centola says.