Dunbar's number

Dunbar's number is an estimate of about 150 stable social relationships that a person can maintain, based on limits on human social cognition.

Social brain hypothesis: The hypothesis that managing social relationships helped drive the evolution of large brains in primates. It supplies the evolutionary explanation linking cognitive capacity to the proposed group-size limit.
Neocortex ratio: The proportion of a brain's volume occupied by the neocortex relative to the rest of the brain. Dunbar used this measure to model primate group size.
Hutterites: A communal Anabaptist Christian people whose settlements organize social life around shared property and work. Reported settlement sizes have been compared with Dunbar's proposed stable-group scale.
Robin Dunbar: A British anthropologist and evolutionary psychologist known for research on primate sociality and human relationships. He proposed the estimate and developed the evidence connecting brain size to group size.
Replication crisis: A concern that findings in several research fields often fail to reproduce in later studies. The estimate's empirical foundations depend on results that must withstand independent tests.
Neocortex: The outer layer of the mammalian brain involved in perception, cognition, and higher-order processing. Dunbar related neocortex size to the size of primate social groups.
Primate social group: A set of primates that regularly interact and maintain social bonds. Observed group sizes were the outcome predicted from neocortex measures.
Company size: The number of people employed by an organization or business. Research has examined whether organizational groups cluster around the proposed limit.
Metcalfe's law: A heuristic that a network's value grows roughly with the square of its number of users. It concerns network value rather than the cognitive limit on maintaining relationships.
Social network analysis: Methods for studying relationships and patterns of connection among social entities. Different network measures can yield different counts of a person's meaningful ties.

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