(Extracted from The Economist 25 Jan 2020; Bartley column titled The Number of the Best)
Dunbar observes that humans tend to have five intimate friends, 15 or so good friends, around 50 social friends and 150-odd acquaintances.
A Roman centurion oversaw 100. The modern American army company has 180 members. Britain’s equivalent numbers 120. The Special Air Service, Britain’s elite fighting unit, has four-man patrols; when your life depends on it, you need to have absolute trust in your colleagues.
“If you want a committee to decide something, limit it to four to five people,” says Mr Dunbar. “But to brainstorm in a meeting, you need 12-15.”