According to MIT researchers, Twitter relied on an ancient form of viral growth to reach 300 million users worldwide – word of mouth.

“Even on the Internet where we may think the world is flat, it’s not,” says Marta González, assistant professor of civil and environmental engineering and engineering systems at MIT, who is co-author of a paper appearing this month in the journal PLoS ONE.

“The big question for people in industry is ‘How do we find the right person or hub to adopt our new app so that it will go viral?’ But we found that the lone tech-savvy person can’t do it; this also requires word of mouth. The social network needs geographical proximity. … In the U.S. anyway, space and similarity matter.”

Researchers looked at the growth of Twitter in 16,000 U.S. cities from 2006 to 2009, focusing on the 408 with the highest number of Twitter users, and found the site’s growth in the United States relied primarily on media attention and traditional social networks based on geographic proximity and socioeconomic similarity.

The growth of Twitter initially spread via young, tech-savvy innovators, hence the birthplace in San Francisco and eventually the greater Boston area, according to the paper.

From there Twitter took a more traditional route of traveling only short distances, implying face-to-face interactions, reaching Somerville, Mass., and Berkeley, Calif. early on.

Traditional media coverage from the likes of Ashton Kutcher and Oprah then catapulted Twitter into the mainstream.