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The Dunbar number (the 150)

The number 150 has a special feature, according to anthropologist Robin Dunbar, this is the number of individuals that a person can maintain a relationship stable.


Robin Dunbar

Dunbar theorizes that this value is related to the size of the neocortex. This related, according to him, with the ability to process this. Source


primatologists (those who study the behavior of primates) in their research, they noted that since to their highly social nature, non-human primates have to maintain personal contact with other members of their social group.
The number of group members a primate can still appears to be limited by the volume of the neocortex. This suggests that there is an index of social group size depending on the species, distinguishable by the volume of the neocortex.

In 1992, Dunbar used the correlation observed in nonhuman primates to predict the size of human social group. Dunbar predicted a group size of 147.8 (usually represented as 150), a result which Dunbar not consider accurate.


The mysterious number 150
Dunbar
compare this prediction with observable group of humans. Beginning with the assumption that the human neocortex development around 250,000 years ago, looked into the anthropological and ethnographic literature for a kind of census sizes of social groups in nomadic societies. Dunbar noted that the groups fell into three categories, 30-50, 100-200, and 500-2500 individuals.

Dunbar's research on the sizes of tribes and villages also appeared to approximate this predicted value, including 150 as the estimated size of a village farmer from the Neolithic era, 150 as the turning point and separation the Hutterite, 200 as the maximum number of scholars in the sub-specialization in a discipline; 150 as the basic size of a professional military unit in ancient Rome and in modern times since the 16th century. Dunbar

theorize that a group with a size of 150 people should have a high incentive to stay together. For a group this size holds that cohesion, Dunbar speculated that at least 42% of the time the group had to be devoted to socialization.


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Correspondingly, only groups under intense pressure to survive, as towns subsistence, nomadic tribes and military groups could, on average, reach the number of 150 members. What's more, Dunbar noticed that such groups are almost always physically close, this would be so because of proximity, as a dispersed group would have fewer ties, to meet less often. Therefore the 150-member groups only occur due to an absolute necessity, for example, an aggressive economic pressure. Dunbar

also suggests that language may have created as an easy way to socialize, since without language humans have had to occupy almost half of their time socializing, which would have made any effort at cooperation production was almost impossible. Language may have allowed societies to remain cohesive, reducing the need for physical and social intimacy.

The Dunbar number then became a topic of interest within anthropology, sociology, statistics and business administration. Like many theoretical values, usually abuse it like a magic number. References


The Dunbar number (English wikipedia)