Your Brain Can Handle About 150 People You Know
The limit came from linking brain size to troop size in monkeys and apes, then applying the same math to people.
Half as Interesting · Why You Can Only Have 150 Friends (According to Science)Your social world has a predicted capacity of about 150 people you know well enough to greet and keep track of. That number did not come from counting human contacts. It came from measuring brain anatomy across many primate species and then extending the pattern to people.
The starting puzzle is why primates, the animal group that includes monkeys, apes, and humans, have unusually large brains for their body size. One set of explanations points to nutrition and digestion. Evolutionary psychologist Robin Dunbar favored a different proposal, called the Machiavellian intelligence hypothesis, which proposes that primates developed larger brains because skill at complex social strategies helped animals achieve greater reproductive success.
In 1992, Dunbar tested that proposal with anatomy. For different primate species, he calculated the size of the neocortex, the wrinkled outer layer involved in thinking and social judgment, relative to total brain volume. He then compared that ratio with the size of each species' typical social group, and found a clear correlation. The larger the neocortex share, the larger the group.
Dunbar then extrapolated that primate relationship to the human brain. The formula predicted an average human group of 148, which he rounded to 150. In Dunbar's argument, that figure reflects how much social calculation a human brain evolved to manage.
Questions people ask
Is 150 a strict limit for everyone?
No, it is an average prediction, not a personal cap. Some people maintain fewer close relationships and some maintain more, depending on age, personality, time, and culture. Researchers treat 150 as the center of a range where keeping track of who is who starts to get hard.
What exactly is the neocortex?
It is the thin, wrinkled outer layer of the mammalian brain that handles perception, language, planning, and social judgment. In primates, and especially in humans, it takes up an unusually large share of the brain. Dunbar used its share of total brain volume as a proxy for computing power for social life.
Do Facebook and phones let us get past 150?
They let people contact more people, but studies of phone records, social media interaction, and Christmas card lists generally find the active core still clusters around 150. Technology makes it easier to stay in touch, but it does not clearly expand how many relationships a person actively manages.