Tom Standage is the digital editor at The Economist and the author of the forthcoming book “Writing on the Wall: Social Media — The First 2,000 Years.”

LONDON — SOCIAL networks stand accused of being enemies of productivity. According to one popular (if questionable) infographic circulating online, the use of Facebook, Twitter and other such sites at work costs the American economy $650 billion each year. Our attention spans are atrophying, our test scores declining, all because of these “weapons of mass distraction.”

Yet such worries have arisen before. In England in the late 1600s, very similar concerns were expressed about another new media-sharing environment, the allure of which seemed to be undermining young people’s ability to concentrate on their studies or their work: the coffeehouse. It was the social-networking site of its day.

Like coffee itself, coffeehouses were an import from the Arab world. England’s first coffeehouse opened in Oxford in the early 1650s, and hundreds of similar establishments sprang up in London and other cities in the following years. People went to coffeehouses not just to drink coffee, but to read and discuss the latest pamphlets and news-sheets and to catch up on rumor and gossip....