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.^[1] 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." This article or section does not adequately cite its references or sources. ... Anthropology (from Greek: ἀνθρωπος, anthropos, human being; and λόγος, logos, knowledge) is the comparative study of the physical and social characteristics of humanity through the examination of historical and present geographical distribution, cultural history, acculturation, and cultural relationships. ... 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 non-human primates. ... Families 15, See classification A primate 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 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). Trinomial name Homo sapiens sapiens Linnaeus, 1758 Humans, or human beings, are bipedal primates belonging to the mammalian species Homo sapiens (Latin: wise man or knowing man) in 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. “Era Vulgaris” redirects here. ... The Pleistocene epoch (IPA: ) is part of the geologic timescale. ... Anthropology (from Greek: ἀνθρωπος, anthropos, human being; and λόγος, logos, knowledge) is the comparative study of the physical and social characteristics of humanity through the examination of historical and present geographical distribution, cultural history, acculturation, and cultural relationships. ... Ethnography (from the Greek ethnos = people and graphein = writing) refers to the genre of writing that presents varying degrees of qualitative and quantitative descriptions 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. ... http://www. ...

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. Masouleh village, Gilan Province, Iran. ... An array of Neolithic artifacts, including bracelets, axe heads, chisels, and polishing tools. ... 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. ... This article or section is in need of attention from an expert on the subject. ... Ancient Rome was a civilization that grew from a small agricultural community founded on the Italian Peninsula circa the 9th century BC to a massive empire straddling the Mediterranean Sea. ... 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 interest in anthropology, sociology, statistics, and business management. A graph of a Normal bell curve showing statistics used in educational assessment and 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. 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. ...

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. Anarchy (from Greek: anarchía, no authority) has a popular meaning of disorder[1]. However it has a more precise meaning in political philosophy to describe any human society which exists without a state. ... The Politics series Politics Portal This box:      Politics is defined as a group of people who are influenced to change laws and other such things to make the world a better place the process by which groups of people make decisions. ... It has been suggested that Tyranny of the Commons be merged into this article or section. ...

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. This article cites very few or no references or sources. ...

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 non-human animals could be reductively explained as automata — De homines 1622. ...

Some sample 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. ... An image from World of Warcraft, one of the largest commercial MMORPGs as of 2004, based on active subscriptions. ... Ultima Online (UO) is a popular graphical massively multiplayer online role-playing game (MMORPG), released on September 25, 1997, by Origin Systems. ... 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 tribal lifestyles has been re-created or re-embraced. ...

References

1. ^ Gladwell, Malcolm (2000). The Tipping Point - How Little Things Make a Big Difference. Little, Brown and Company. ISBN 0-316-34662-4. 

Further reading

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.