How many friends do you have? Science says it’s less than 150

This week’s entry: Dunbar’s number

What it’s about: At some point in the 1990s, British anthropologist Robin Dunbar posited that people can only maintain 150 stable social relationships. He very scientifically qualifies that as “the number of people you would not feel embarrassed about joining uninvited for a drink if you happened to bump into them in a bar,” and since then, Dunbar’s number has been widely accepted in social science. Dunbar also determined that we devote 40% of our “social time” to the five people closest to us, and another 20% to the next closest 10.

Strangest fact: Dunbar drew his conclusions from the objectively best branch of science: monkey science. Social cohesion is important to primates of all kinds (humans included), and Dunbar noticed a correlation between the size of primates’ brains and the size of their social groups. The more brain cells, the more social relationships they (and we) can track. Based on the size of the human brain, he predicted an average human social network size of 148 (which he then rounded up). His research found that the same magic number applied to the estimated size of neolithic farming villages, the average Hutterite settlement (Anabaptist communes that split in two after growing too big), and army units from Roman times to the present.

Thing we were happiest to learn: People took Dunbar’s research seriously. W. L. Gore And Associates, the company that produces Gore-Tex and other polymer-related products, limits the size of their offices to 150 employees. Rather than expand any branch of the company beyond that number, Gore opens another office, even if it’s close to an existing branch. The Swedish tax authority also planned to organize around similar principles in 2007. But did they? Wikipedia doesn’t say. Don’t keep us in suspense, Swedish tax authority!

Thing we were unhappiest to learn: Not everyone agrees with Dunbar. Brown University cognitive scientist Philip Lieberman attacks the number from both sides. On one hand, he argues, prehistoric humans couldn’t have supported social groups as large as 150 before the advent of agriculture, so it doesn’t make sense that we’d evolve to have a larger social circle than a hunting group. (We would counter-argue that evolution is rarely so precise, and traits don’t have to be advantageous to be part of our makeup; they just have to not be a disadvantage.) Lieberman’s other, stronger argument is that animals with tiny brains still manage large social circles. Paper wasps, for instance, have social hierarchies of up to 80 insects.

Also noteworthy: John Dies At The End author David Wong explained Dunbar’s number (without mentioning Dunbar) in a 2007 piece for Cracked called “What Is The Monkeysphere?” His analogy was, if you had one pet monkey, you’d give that monkey a name and have affection for it. Same with four or five monkeys. But confronted with a million monkeys, you wouldn’t give them names or care much if a few of them died. He used this to lead into the simian research that informed Dunbar’s work. He also addressed Dunbar’s number in his 2012 novel, The Book Is Full Of Spiders, in which a character claims Dunbar’s number explains xenophobia and why some people are incapable of empathy for those outside their immediate circle.

Best link to elsewhere on Wikipedia: Another interesting bit of social biology is dual inheritance theory, which answers the age-old “nature vs. nurture” question with the “why not both?” meme. DIT suggests that both genetics and culture evolve over time, each influencing the other. For example, we evolved to have different-shaped teeth and smaller stomachs than apes because we learned to cook our food, which requires less chewing and stomach acid to break down than raw food. (Apparently, chimps spend six hours a day chewing; American children spend less than two.)

Further down the Wormhole: Whether it’s modern army companies being the same size as those in Roman legions, or high-speed rail being the same width apart as the ruts made by Roman chariots, the unconscious influence of Ancient Rome is everywhere. The two pivotal figures in Rome’s transition from republic to empire, Julius Caesar, and his general, Mark Antony, each had an affair (and fathered children) with Cleopatra, the last pharaoh to rule Egypt before that empire was subsumed into Rome’s. Cleopatra has been the subject of countless works of art, among them The Triumph Of Cleopatra, William Etty’s 1821 painting that made him famous, and scandalized England for its many nude figures. Etty atoned for his frequent use of nudes by painting The Destroying Angel And Daemons Of Evil Interrupting The Orgies Of The Vicious And Intemperate. We’ll take a look at Etty’s moralizing painting and its catchy title next week.