Dunbar's Number

Discussion

In the very long and relatively stable history of human evolution, people lived in loose communities in which they knew everyone. The Social Brain Hypothesis (originally the Machiavellian Intelligence Hypothesis) suggests that the human brain is larger because it allows us to live in socially complex societies. This is noted particularly in the size of the frontal lobe of the neocortex where social juggling takes place.

This is one reason why small communities and companies thrive well up to around Dunbar's number. After that, they go through a barrier beyond which not everyone knows everyone that well and the social dynamics change.

Dunbar is an anthropologist who studied the size of groups (as well as the development of language and brain size). By correlating group size and brain size across a range of 36 types of primate, he interpolated the human 'mean group size' as 147.8. Given natural variation, 150 is a reasonable round number.

Dunbar also concluded that, in order for a group of this size to remain together, 42% of its members' time should be spent in social grooming, building trust and social capital. A key point about this is that grooming time steadily increases with group size, and that there is a natural crossover point where a larger group would result in conflict in time spent between grooming and other sustaining activities.

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Dunbar's Number

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