Dunbar's number

See also: Dunbar (disambiguation)

Dunbar's number, which is 150, represents a theoretical maximum number of individuals with whom a set of people can maintain a social relationship, the kind of relationship that goes with knowing who each person is and how each person relates socially to every other person. Group sizes larger than this generally require more restricted rules, laws, and enforced policies and regulations to maintain a stable cohesion. Dunbar's number is a significant value in sociology and anthropology. Proposed by British anthropologist Robin Dunbar, it indicates the "cognitive limit to the number of individuals with whom any one person can maintain stable relationships". Dunbar theorizes 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." On the periphery, the number 150 also includes old colleagues and old high school friends that you meet again years later and reacquaint with each other's history,

"You would probably have to do a lot of catching up, but they know you fit into their social world and you know they fit into yours. You have a history."—Robin Dunbar

This will be my final edit. The wikipedia people will now ban me. goodbye fools......... bye...

Research background

Primatologists have noted that, due to their highly social nature, non-human primates have to maintain personal contact with the other members of their social group, usually through grooming. Such social groups function as protective cliques within the physical groups in which the primates live. The number of social group members a primate can track appears to be limited by the volume of the neocortex region of their brain. This suggests that there is a species-specific index of the social group size, computable from the species' mean neocortex volume.

In a 1992 article, Dunbar used the correlation observed for non-human primates to predict a social group size for humans. Using a regression equation on data for 38 primate genera, Dunbar predicted a human "mean group size" of 147.8 (casually represented as 150), a result he considered exploratory due to the large error measure (a 95% confidence interval of 100 to 230).

Dunbar then compared this prediction with observable group sizes for humans. Beginning with the assumption that the current mean size of the human neocortex had developed about 250,000 years BCE, i.e. 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. 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.

Dunbar'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-specialization; 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 has theorized that 150 would be the mean group size only for communities with a very high incentive to remain together. 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. Correspondingly, only groups under intense survival pressure, such as subsistence villages, nomadic tribes, and historical military groupings have, on average, achieved the 150-member mark. Moreover, Dunbar noted that such groups are almost always physically close: "... we might expect the upper limit on group size to depend on the degree of social dispersal. In dispersed societies, individuals will meet less often and will thus be less familiar with each, so group sizes should be smaller in consequence." Thus, the 150-member group would only occur because of absolute necessity, i.e. due to intense environmental and economic pressures.

Dunbar, author of Grooming, Gossip, and the Evolution of Language, proposes furthermore that language may have arisen as a "cheap" means of social grooming, allowing early humans to efficiently maintain social cohesion. Without language, Dunbar speculates, humans would have to expend nearly half their time on social grooming, which would have made productive, cooperative effort nearly impossible. Language may have allowed societies to remain cohesive, while reducing the need for physical and social intimacy.

Dunbar's number has since become a major interest in anthropology, sociology, evolutionary psychology, statistics, and business management.

Popularization

• Dunbar's number has been most popularized by Malcolm Gladwell's The Tipping Point, where it plays a central role in Gladwell's arguments about the dynamics of social groups.

• In a 1985 paper titled "Psychology, Ideology, Utopia, & the Commons," psychologist Dennis Fox proposed the same concept as it is applied to anarchy, politics, and the tragedy of the commons.

• It has also been popularized as the monkeysphere, a neologism coined by David Wong in an article, Inside the Monkeysphere, which introduces this concept in a humorous manner.

• Neo-Tribalists have also used it to support their critiques of modern society.

• Recently, the number has been used in the study of Internet communities, especially MMORPGs such as Ultima Online, and social networking websites such as Facebook and MySpace.

"It's perfectly possible that the technology will increase your memory capacity."—Robin Dunbar

Further reading

• Dunbar, R.I.M. (1992) Neocortex size as a constraint on group size in primates, Journal of Human Evolution 22: 469-493.

• Dunbar, R.I.M. (1993), Coevolution of neocortical size, group size and language in humans, Behavioral and Brain Sciences 16 (4): 681-735.

• Edney, J. J. (1981a). Paradoxes on the commons: Scarcity and the problem of equality. Journal of Community Psychology, 9, 3-34.

• Sawaguchi, T., & Kudo, H. (1990), Neocortical development and social structure in primates, Primates 31: 283-290.

External links

• A pre-publication version of Coevolution of neocortical size, group size and language in humans. (See also Bibliography section there.)
• University of Liverpool Research Intelligence No. 17, August 2003 - "The ultimate brain teaser" - an article on Dunbar's research.
• Inside the Monkeysphere by David Wong - a humorous introduction to the notion of the monkeysphere.
• Some speculations about a correlation between the monkeysphere and guild size in online multiplayer role playing games.
• Detailed article about Dunbar's number and its application to online gaming
• Mospos blog entry - Communities of practice and Dunbar's number
• Life With Alacrity blog entry - A blog on social software, collaboration, trust, security, privacy, and internet tools, by Christopher Allen.