The number of Dunbar (Dunbar's number) is a theoretical limit cognitive ability to determine the approximate number of people that individuals can maintain a stable social relationships. These relationships are those that a person can know who each person making up a network of social relations. Although the value determined at 150, is not entirely accurate, being commonly cited as a consistent approach.
This theory was proposed by British anthropologist Robin Dunbar, research professor of evolutionary anthropology at Oxford University. Dunbar, in 1992, observed a correlation was used to nonhuman primates in order to determine the size of social groups of humans, where predicted a group of 147.8, usually represented as 150. Still, Robin Dunbar was not considered accurate because it is related to the volume of brain Neocortex. Also suggests a difference in the rate of social group size according to species, established by the differential volume of neocortex.
From this experience, made a comparison with observable human groups. Looking into the anthropological and ethnographic literature, conducted a census on the size of social groups within nomadic societies where it determined that the groups were classified into three categories, 30 to 50, 100 to 200 and 500 to 2500 . His research on the social dimension of the tribes seem closer to the prediction, where the size was a Neolithic settlement is approximately 150 people. 150 also sets the point of excision of a settlement huterita. In the military context, establishes the basic size of a professional military unit in ancient Rome and on the contemporaneous times since the sixteenth century. As approximation, 200 members are the maximum allowed in an sub-specialization of academic discipline. Dunbar theorized about this vision that a group size of 150 people, he needed a very high incentive to maintain the union, speculating that at least 42% of the time the group was engaged in sociability, where the language is primarily developed to limit the amount of time. Moreover, argues that the language is an effective device for maintaining social relations, as animals generate more physical activity to keep them, against the social productivity, and that not only is the limit of stable relationships that a person be maintained, but may indicate the limit of people who can become an organic group without a stable pyramidal structure of authority. In the words of Dunbar:
"… there is a cognitive limit to the number of individuals with whom any one person can maintain stable relationships, that this limit is a direct function of relative neocortex size, and that this in turn limits group size"
Dunbar, R. I. M. (1993). Coevolution of neocortical size, group size and language in humans. Behavioral and Brain Sciences 16 (4): 681-735.
Wherefore now an application in the management of social policies, such as socialism, fascism and other centralized ideologies, they can operate properly on a small scale, but the when grown index of population, the social cohesion problems arise because of the difficulty maintain adequately controlled relationships between individuals.
The number of Dunbar's theory is applicable to problems of overpopulation, due to the remoteness of the social group average of 150 hypothetical system in any delimited, for example a city, increasing the likelihood of emergence of conflict, which would nowadays, environmental pollution, disorder public, discrimination or criminal acts or criminal. The number of Dunbar has been studied by anthropologists as a hot topic, to applying theories in marketing and social networking, to study groups of people in virtual worlds and social spaces created electronically. A clear example is social networks like Facebook, Tuenti or other similar characteristics, which provides a significant increase in the number of Dunbar that breaks the direct relationship and the physical process of interaction.
Cameron Barlow, a sociologist who researches on relations within Facebook, confirms the theory of number Dunbar in their application to social networks, which states that Facebook users communicate regularly with only a small core of your friends list . Robin Dunbar himself was revised his theory by applying it on Facebook, in a study to be published later this year where he compared the traffic of thousands of people who are friends with others who have hundreds or less without find a substantial difference between them, thereby confirming his theory, with Barlow, that the brain can not expand their capacity to have meaningful relationships with more people, even within the virtual world. The results of Durban showed a clear diference by gender, where women were better than men to maintain virtual relationships. For them easier to maintain a relationship just talking with friends, while men show a greater need for physical interaction.