Other papers by Dr. Hampton argue that the internet and social media can facilitate offline social connections. One states that “internet use may be associated with higher levels of participation in traditional settings that support the formation of diverse networks,” such as visiting public spaces or knowing more people in the neighborhood. Another suggests that frequent Facebook users have more close and more diverse social ties than the average American — though roughly the same number of overall connections.

Wedding and Funeral Guests

These findings jibe with the research of Robin Dunbar, a professor of evolutionary psychology at Oxford. He has theorized that “group size” of both humans and nonhuman primates — the number of people (or, say, chimpanzees) one can maintain social cohesion with — correlates to “relative neocortical volume,” or the ratio of the neocortex to the rest of the brain.

The oft-cited “Dunbar’s number” is an average of 150 casual friends for humans (really, a range of 100 to 200). These are the people who might come to your wedding or funeral.

Within this roster, there are embedded layers of intimacy that grow smaller by a factor of three: 50 of these make the next cut to buddies, about 15 are good friends, around five confidants form our circle of trust, and finally we have an average of 1.5 people we deem our closest relationships. (Conversely, we can keep track of roughly 500 acquaintances and 1,500 faces we can match to names.)

One may presume that boasting thousands of social media friends or followers would inflate Dunbar’s number, but Dr. Dunbar said that is “absolutely not at all” the case. In a recent paper analyzing Facebook and Twitter data, and another one looking at mobile phone calls, his team determined that people still “showed the same frequencies of interaction as in face-to-face relationships” for the corresponding layers of intimacy, he said.

However, digital media channels “don’t distinguish between quality of relationships,” he said. “They allow you to maintain relationships that would otherwise decay. Our data shows that if you don’t meet people at the requisite frequencies, you’ll drop down through the layers until eventually you drop out of the 150 and become ‘somebody you once knew.’ What we think is happening is that, if you don’t meet sometime face to face, social media is slowing down the rate of decay.”