"The figure of 150 seems to represent the maximum number of individuals with whom we can have a genuinely social relationship, the kind of relationship that goes with knowing who they are and how they relate to us,” Dunbar has written. “Putting it another way, it’s 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.”

Whereas baboons bond by taking turns picking each others’ nits, we have rhetoric and gossip and half-time speeches, not to mention singing and storytelling and jokes, to bring and hold us together. Language, he says, is how humans used their big brains to get to 150. And until something as revolutionary as that comes along, 150 is where he thinks we’ll stay.