Dunbar's Number

The cognitive limits of friendship and what they mean for how you invest social time

What is Dunbar's number and what does it mean for your friendships?

Robin Dunbar's research proposes that the human neocortex supports a stable social group of roughly 150 people, with nested layers of closer relationships (5, 15, 50) requiring progressively more time investment to maintain. The 150-person figure has observational support across hunter-gatherer societies, historical military units, and company sizes; the nested-layer model is more contested. The practical implication is that meaningful relationships are a limited resource that require deliberate allocation.

Most people have more acquaintances than they can actively maintain and fewer close friends than they would like. Robin Dunbar's research suggests this is not a personal failing but a cognitive constraint: the social brain can only track and maintain so many relationships at the complexity required for genuine friendship. Understanding Dunbar's number re-frames social life from a popularity contest into a portfolio management problem — one where the goal is deliberate investment, not maximum reach.

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