Dunbar's number: can we really only juggle about 150 relationships?

In the 1990s, anthropologist Robin Dunbar noticed that across primate species, bigger brains — specifically a larger neocortex — went with bigger social groups. Extrapolating to humans, he proposed a natural limit of about 150 stable relationships: people whose name, face and connection to others you can genuinely keep track of. It became known as Dunbar’s number.

Dunbar argues these relationships nest in layers: roughly 5 intimate ties, 15 close friends, 50 friends and 150 meaningful contacts — with up to ~1,500 faces you merely recognize. He says the same layered pattern shows up in other social mammals.

But the number is disputed. A 2021 re-analysis concluded the primate data can’t pin down any single human figure — estimates ranged from the teens to over a hundred, with confidence intervals so wide that “a cognitive limit on human group size cannot be derived in this manner.”

Dunbar counters that the critics used a statistical method that understates the true value.

A neat idea, then — robustly debated rather than robustly proven.