Dunbar's number (also known as the Dunbar number or the Monkeysphere) is a value significant in sociology and anthropology. Proposed by British anthropologist Robin Dunbar, it measures 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." Social interactions of people and their consequences are the subject of sociology studies. ... Anthropology (from the Greek word άνθρωπος, human or person) consists of the study of humanity (see genus Homo). ... Robin Dunbar is an evolutionary biologist, specialising in primate behaviour. ... The neocortex (Latin for new bark or new rind) is a part of the brain of mammals. ...

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. Primatology is the study of primates. ... Families 15, See classification A primate (L. prima, first) is any member of the biological order Primates, the group that contains all the species commonly related to the lemurs, monkeys, and apes, with the latter category including humans. ...

In a 1993 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 36 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). Trinomial name Homo sapiens sapiens Linnaeus, 1758 Humans, or human beings, are bipedal primates belonging to the mammalian species Homo sapiens (Latin for wise man or knowing man) under the family Hominidae (the great apes). ...

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. The Common Era (CE or C.E.), sometimes known as the Current Era or Christian Era, is the period of measured time beginning with the year 1 (the traditional birthdate of Jesus) to the present. ... The Pleistocene epoch (pronounced like ply-stow-seen) is part of the geologic timescale. ... Anthropology (from the Greek word άνθρωπος, human or person) consists of the study of humanity (see genus Homo). ... Ethnography (from the Greek ethnos = nation and graphein = writing) refers to the qualitative description of human social phenomena, based on fieldwork. ... In anthropology, the hunter-gatherer way of life is that led by certain societies of the Neolithic Era based on the exploitation of wild plants and animals. ... A Band Society is the simplest form of human society. ... A tribe, viewed historically or developmentally, consists of a social group existing before the development of, or outside of, states, though some modern theorists hold that contemporary tribes can only be understood in terms of their relationship to states. ...

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. A village is a human residential settlement commonly found in rural areas. ... An array of Neolithic artefacts, including bracelets, axe heads, chisels, and polishing tools Excavated dwellings at Skara Brae Scotland, Europes most complete Neolithic village. ... Hutterite women at work Hutterites are a communal branch of Anabaptists who, like the Amish and Mennonites, trace their roots to the Radical Reformation of the 16th century. ... Army (from French armée) can, in some countries, refer to any armed force. ... The Roman Forum was the central area around which ancient Rome developed. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

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. Like most farmers in Sub-Saharan Africa, this Cameroonian man cultivates at the subsistence level. ... Kazakh nomads in the steppes of the Russian Empire, ca. ...

Dunbar 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 meme of interest in anthropology, sociology, statistics, and business management. As with many theoretical values, it has occasionally been abused and mistaken as a "magic number". The term meme (IPA: ), coined in 1976 by Richard Dawkins, refers to a replicator of cultural information that one mind transmits (verbally or by demonstration) to another mind. ... A graph of a bell curve in a normal distribution showing statistics used in educational assessment, comparing various grading methods. ... Management (from Old French ménagement the art of conducting, directing, from Latin manu agere to lead by the hand) characterises the process of leading and directing all or part of an organization, often a business, through the deployment and manipulation of resources (human, financial, material, intellectual or intangible). ...

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. Malcolm Gladwell Malcolm Gladwell (born September 1, 1963) is a United Kingdom-born, Canadian-raised journalist now based in New York City who has been a staff writer for The New Yorker since 1996. ... The Tipping Point (ISBN 0316316962) is a book by Malcolm Gladwell, first published by Little Brown in 2000. ... from, pak wan punk bkt mertajam penang Anarchy (Greek: αναρχία) is the anarchist society, the stateless society of free people. ... Politics is a process by which decisions are made within groups. ... The tragedy of the commons is a phrase used to refer to a class of phenomena that involve a conflict for resources between individual interests and the common good. ...

It has also been popularized as the monkeysphere, a neologism coined by David Wong in an article which introduces this concept in a humorous manner. A neologism is a word, term, or phrase which has been recently created (coined) — often to apply to new concepts, or to reshape older terms in newer language form. ...

In its popularization, the research of Dunbar and others is taken as an upper bound of the number of fellow humans that an individual can view as being "truly human". In this form, the "monkeysphere" functions as a reductionistic and biologistic explanation for why humans can treat some humans with consideration and other humans indifferently or even inhumanely. Descartes held that, unlike humans, animals could be reductively explained as automata – De homines 1622) Reductionism in philosophy is a theory that asserts that the nature of complex things can always be reduced to (explained by) simpler or more fundamental things. ...

Some example explanations using the notion of a monkeysphere are:

• "Whenever you make new close personal friends, you have to drop some old personal friends to make room for them in your monkeysphere."
• "The reason that the people in village X don't mind doing Y to the people in village Z is because the people in village Z are not in the monkeysphere of people in village X."
• "Because the number of people in that department exceeded 150, which is the size of the human monkeysphere, they had to split the department into two."

Recently, the number has been used in the study of Internet communities, especially MMORPGs such as Ultima Online. Neo-Tribalists have also used it to support their critiques of modern society. A virtual community is a group whose members are connected by means of information technologies, typically the Internet. ... Players interacting in Ultima Online. ... Released on September 30, 1997, by Origin Systems, Ultima Online (UO) is a popular graphical massively multiplayer online role-playing game that was instrumental to the development of the genre, and is still running today. ... Neo-Tribalism is the ideology that human beings have evolved to live in a tribal, as opposed to a modern, society, and thus cannot achieve genuine happiness until some semblance of archaic lifestyles has been re-created or re-embraced. ...

References

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. (404)
• 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.