Dunbar number

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Cranium size

• Robin Dunbar (2003) found a correlation between the average social group size in mammals and their cranium size.
• By using the average human brain size and extrapolating from the results of primates, he proposed that humans can comfortably maintain 150 stable relationships.
  • "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".
• Dunbar suggests:
  • "this limit is a direct function of relative neocortex size, and that this in turn limits group size ... the limit imposed by neocortical processing capacity is simply on the number of individuals with whom a stable inter-personal relationship can be maintained".
• He also claims that humans devote around two-thirds of their time to only 15 people and that we work with an inner core of about 5 people (40 percent of available social time) plus 10 more to whom we devote another 20 percent. 

Further Reading

• Hill, R.A. and Dunbar, R.I., 2003. Social network size in humans. Human nature, 14(1), pp.53-72.