For a group of this size to remain cohesive, Dunbar speculated that as much as 42% of the group's time would have to be devoted to social grooming. ĭunbar has argued that 150 would be the mean group size only for communities with a very high incentive to remain together.
FRIENDS AND FAMILY 1 WORKBOOK PROFESSIONAL
ĭunbar's surveys of village and tribe sizes also appeared to approximate this predicted value, including 150 as the estimated size of a Neolithic farming village 150 as the splitting point of Hutterite settlements 200 as the upper bound on the number of academics in a discipline's sub-specialisation 150 as the basic unit size of professional armies in Roman antiquity and in modern times since the 16th century and notions of appropriate company size. Dunbar noted that the groups fell into three categories-small, medium and large, equivalent to bands, cultural lineage groups and tribes-with respective size ranges of 30–50, 100–200 and 500–2500 members each. Beginning with the assumption that the current mean size of the human neocortex had developed about 250,000 years ago, during the Pleistocene, Dunbar searched the anthropological and ethnographical literature for census-like group size information for various hunter–gatherer societies, the closest existing approximations to how anthropology reconstructs the Pleistocene societies. ĭunbar then compared this prediction with observable group sizes for humans. Using a regression equation on data for 38 primate genera, Dunbar predicted a human "mean group size" of 148 (casually rounded to 150), a result he considered exploratory because of the large error measure (a 95% confidence interval of 100 to 230). In 1992, Dunbar used the correlation observed for non-human primates to predict a social group size for humans. This suggests that there is a species-specific index of the social group size, computable from the species' mean neocortical volume. The number of social group members a primate can track appears to be limited by the volume of the neocortex. Such social groups function as protective cliques within the physical groups in which the primates live. Primatologists have noted that, owing to their highly social nature, primates must maintain personal contact with the other members of their social group, usually through social grooming.
Ī replication of Dunbar's analysis with a larger data set and updated comparative statistical methods has challenged Dunbar's number by revealing that the 95% confidence interval around the estimate of maximum human group size is much too large (4–520 and 2–336, respectively) to specify any cognitive limit. It has been proposed to lie between 100 and 250, with a commonly used value of 150. Proponents assert that numbers larger than this generally require more restrictive rules, laws, and enforced norms to maintain a stable, cohesive group. On the periphery, the number also includes past colleagues, such as high school friends, with whom a person would want to reacquaint themselves if they met again. Dunbar explained it informally as "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 theorised that "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". There is some evidence that brain structure predicts the number of friends one has, though causality remains to be seen. By using the average human brain size and extrapolating from the results of primates, he proposed that humans can comfortably maintain 150 stable relationships. This number was first proposed in the 1990s by British anthropologist Robin Dunbar, who found a correlation between primate brain size and average social group size. Dunbar's number is a suggested cognitive limit to the number of people with whom one can maintain stable social relationships-relationships in which an individual knows who each person is and how each person relates to every other person.
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