Everyone knows that you want skinny jeans tucked into your boots. Ten years ago everyone knew that you wanted boot cut jeans to go over your boots. But how does everyone know these things? How does one option out of all the possible alternatives get chosen as the standard and then reach universal acceptance?

The origin and emergence of social conventions has long beguiled cognitive scientists, sociologists, linguists, and philosophers. Prominent ideas have assumed that institutionalized mechanisms—like a centralized authority or incentives for collective agreement—are required for shared conventions to become prevalent. Newer social evolutionary ideas, by contrast, have suggested that networks of locally interacting individuals can spontaneously and unintentionally self-organize to produce global coordination, even in the absence of formal institutions.

This sort of self-organization has been very difficult to demonstrate, especially on any meaningful scale. Now, a mathematician and a sociologist have teamed up to show that global social conventions can in fact emerge spontaneously from local interactions, even though the people involved have no idea that they are coordinating anything. There's just one condition: the people have to be hyperconnected.

The researchers recruited people from the Internet to play The Name Game. Participants were seated in front of a computer screen and shown a photo of a blond woman, and they had to give her a name within twenty seconds. They were paired with a partner about whom they had no knowledge. If the two partners agreed on a name for the woman on their screens, they each got fifty cents; if they didn't, they were each docked a quarter. Then they went on to a new round with a new partner. Although they were rewarded for coordinating locally, they had no incentives for—or information about—any sort of global consensus. A standard game was thirty rounds.

Three types of social networks were tested. One was a spatial network, in which partners were chosen only from neighbors or next-nearest neighbors; another was a random network, in which partners were not restricted spatially but were limited to the same four degrees of separation as the spatial network; the last was a homogenous network in which all bets were off—anyone could be partners with anyone else. Participants knew nothing about the structure of the network they were in.

Participants in the spatial and random networks formed groups of agreement early on, but the results were limited. By the end of the game, the most popular name was used by at most forty-five percent of participants, while a maximum of seventy-five percent of partners reached agreement.

Success was slower to come to the homogeneously mixed network, but when it arrived it was more robust. Since people in this network were less likely to interact with the same partner repeatedly, insular "neighborhoods" that used a particular name couldn't form. This local failure only served to spur global coordination; one name always became universally accepted in this network, usually by round twenty-two. Partners who had never even interacted by this point were still able to get it. And this result held true, on the same time scale, when this network size was doubled to ninety-six participants.

The authors think that their results "will be of interest to researchers investigating the effects of online connectedness on the emergence of new political, social, and economic behaviors" and think it will be interesting "to explore the practical implications of the unintended effects of increasing social connectedness on the homogenization of behaviors and beliefs among large numbers of individuals who do not even know that they are implicitly coordinating with one another."

And that's how we'll know which style of jeans to buy next year.

PNAS, 2014. DOI: 10.1073/pnas.1418838112 (About DOIs).