Is it possible to have more than five very close friends? A miscellany of modern research reveals the life-saving power of our relationships

“There is nothing to which nature seems so much to have inclined us, as to society,” wrote Montaigne in “Of Friendship”, an essay celebrating and mourning his BFF, Etienne de La Boétie. According to research cited by the evolutionary psychologist Robin Dunbar, however, men are much less likely to have a “best friend forever” than women, who are more socially skilled in general. This finding might have surprised Montaigne, who supposed women lacked the “constancy of mind” even to be adequate friends to their husbands.

Dunbar belongs in the rarefied ranks, along with Avogadro and Euler, of those who have had a number named after them. His own is 150, which represents a rough cognitive limit to the number of people we can have a stable social relationship with, and so is more or less the natural human group size. In this pleasantly chatty book, a miscellany of modern research on sociableness, he rehearses this argument and his other famous idea – that language evolved so that gossip could replace time-consuming mutual grooming – as well as citing lots of other social-science experiments. Some, to be sure, will not amaze anyone who is not a literal extraterrestrial: “We gain a surprising amount of information from the nonverbal cues that we wrap around our words when we speak,” for example, though it’s not surprising at all. Others are more interesting: the fact, for example, that people who sing together in choirs subsequently enjoy an increased pain threshold, or that conversations involving more than four people are unstable and will usually split into two.