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(???) Dunbar's number =
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(???) Introduction
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(???) unbar's number is a suggested cognitive limit to the number of people
(???) ith whom one can maintain stable social relationships—relationships
n which an individual knows who each person is and how each person
(???) elates to every other person.
(TN3) his number was first proposed in the 1990s by British anthropologist
(???) obin Dunbar, who found a correlation between primate brain size and
(???) verage social group size. By using the average human brain size and
(???) xtrapolating from the results of primates, he proposed that humans
(???) an comfortably maintain 150 stable relationships. There is some
(???) vidence that brain structure predicts the number of friends one has,
(???) hough causality remains to be seen.
(???) unbar explained the principle informally as "the number of people you
(???) ould not feel embarrassed about joining uninvited for a drink if you
(HTM) appened to bump into them in a bar." Dunbar theorised that "this
(???) imit is a direct function of relative neocortex size, and that this,
n turn, limits group size [...] the limit imposed by neocortical
(PNG) rocessing capacity is simply on the number of individuals with whom a
(SND) table inter-personal relationship can be maintained". On the
(PNG) eriphery, the number also includes past colleagues, such as high
(SND) chool friends, with whom a person would want to reacquaint themselves
f they met again. Proponents assert that numbers larger than this
(GIF) enerally require more restrictive rules, laws, and enforced norms to
(???) aintain a stable, cohesive group. It has been proposed to lie between
(DIR) 00 and 250, with a commonly used value of 150.
(???) Research background
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(???) rimatologists have noted that, owing to their highly social nature,
(PNG) rimates must maintain personal contact with the other members of
(???) heir social group, usually through social grooming. Such social
(GIF) roups function as protective cliques within the physical groups in
(???) hich the primates live. The number of social group members a primate
(???) an track appears to be limited by the volume of the neocortex. This
(SND) uggests that there is a species-specific index of the social group
(SND) ize, computable from the species' mean neocortical volume.
(IMG) n 1992, Dunbar used the correlation observed for non-human primates
(???) o predict a social group size for humans. Using a regression equation
(???) n data for 38 primate genera, Dunbar predicted a human "mean group
(SND) ize" of 148 (casually rounded to 150), a result he considered
(???) xploratory because of the large error measure (a 95% confidence
nterval of 100 to 230).
(???) unbar then compared this prediction with observable group sizes for
(HTM) umans. Beginning with the assumption that the current mean size of
(???) he human neocortex had developed about 250,000 years ago, during the
(???) leistocene, Dunbar searched the anthropological and ethnographical
(???) iterature for census-like group size information for various
(HTM) unter-gatherer societies, the closest existing approximations to how
(???) nthropology reconstructs the Pleistocene societies. Dunbar noted that
(???) he groups fell into three categories—small, medium and large,
(???) quivalent to bands, cultural lineage groups and tribes—with
(???) espective size ranges of 30-50, 100-200 and 500-2500 members each.
(???) unbar's surveys of village and tribe sizes also appeared to
(???) pproximate this predicted value, including 150 as the estimated size
(???) f a Neolithic farming village; 150 as the splitting point of
(???) utterite settlements; 200 as the upper bound on the number of
(???) cademics in a discipline's sub-specialisation; 150 as the basic unit
(SND) ize of professional armies in Roman antiquity and in modern times
(SND) ince the 16th century, as well as notions of appropriate company
(SND) ize.
(???) unbar has argued that 150 would be the mean group size only for
(???) ommunities with a very high incentive to remain together. For a group
(???) f this size to remain cohesive, Dunbar speculated that as much as 42%
(???) f the group's time would have to be devoted to social grooming.
(???) orrespondingly, only groups under intense survival pressure, such as
(SND) ubsistence villages, nomadic tribes, and historical military
(GIF) roupings, have, on average, achieved the 150-member mark. Moreover,
(???) unbar noted that such groups are almost always physically close:
(???) [...] we might expect the upper limit on group size to depend on the
(DOC) egree of social dispersal. In dispersed societies, individuals will
(???) eet less often and will thus be less familiar with each other, so
(GIF) roup sizes should be smaller in consequence." Thus, the 150-member
(GIF) roup would occur only because of absolute necessity—because of
ntense environmental and economic pressures.
(???) unbar, in 'Grooming, Gossip, and the Evolution of Language', proposes
(???) urthermore that language may have arisen as a "cheap" means of social
(GIF) rooming, allowing early humans to maintain social cohesion
(???) fficiently. Without language, Dunbar speculates, humans would have to
(???) xpend nearly half their time on social grooming, which would have
(???) ade productive, cooperative effort nearly impossible. Language may
(HTM) ave allowed societies to remain cohesive, while reducing the need for
(PNG) hysical and social intimacy. This result is confirmed by the
(???) athematical formulation of the social brain hypothesis, that showed
(???) hat it is unlikely that increased brain size would have led to large
(GIF) roups without the kind of complex communication that only language
(???) llows.
(???) Applications
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(???) unbar's number has become of interest in anthropology, evolutionary
(PNG) sychology, statistics, and business management. For example,
(DOC) evelopers of social software are interested in it, as they need to
(???) now the size of social networks their software needs to take into
(???) ccount; and in the modern military, operational psychologists seek
(SND) uch data to support or refute policies related to maintaining or
mproving unit cohesion and morale. A recent study has suggested that
(???) unbar's number is applicable to online social networks and
(???) ommunication networks (mobile phone). Participants of the European
(???) areer-oriented online social network XING who have about 157 contacts
(???) eported the highest level of job offer success, which also supports
(???) unbar's number of about 150.
(TN3) here are discussions in articles and books, of the possible
(???) pplication of using Dunbar's number for analyzing distributed,
(DOC) ynamic terrorist networks, cybercrime networks, or networks preaching
(???) riminal ideology.
(???) Alternative numbers
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(???) nthropologist H. Russell Bernard, Peter Killworth and associates have
(DOC) one a variety of field studies in the United States that came up with
(???) n estimated mean number of ties, 290, which is roughly double
(???) unbar's estimate. The Bernard-Killworth median of 231 is lower,
(???) ecause of an upward skew in the distribution, but still appreciably
(???) arger than Dunbar's estimate. The Bernard-Killworth estimate of the
(???) aximum likelihood of the size of a person's social network is based
(???) n a number of field studies using different methods in various
(PNG) opulations. It is not an average of study averages but a repeated
(???) inding. Nevertheless, the Bernard-Killworth number has not been
(PNG) opularized as widely as Dunbar's.
(???) Criticism
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(???) replication of Dunbar's analysis on updated complementary datasets
(???) sing different comparative phylogenetic methods yielded wildly
(DOC) ifferent numbers. Bayesian and generalized least-squares phylogenetic
(???) ethods generated approximations of average group sizes between 69-109
(???) nd 16-42, respectively. However, enormous 95% confidence intervals
(???) 4-520 and 2-336, respectively) implied that specifying any one number
s futile. The researchers drew the conclusion that a cognitive limit
(???) n human group size cannot be derived in this manner. The researchers
(???) lso criticised the theory behind Dunbar's number because other
(PNG) rimates' brains do not handle information exactly as human brains do,
(???) ecause primate sociality is primarily explained by other factors than
(???) he brain, such as what they eat and who their predators are, and
(???) ecause humans have a large variation in the size of their social
(???) etworks. Dunbar commented the choice of data for this study, however,
(???) ow stating that his number should not be calculated from data on
(PNG) rimates or anthropoids, as in his original study, but on apes. This
(???) ould mean that his cognitive limit would be based on 16 pair-living
(GIF) ibbon species, three solitary orangutans, and only four group living
(GIF) reat apes (chimpanzees, bonobos and two gorilla species), which would
(???) ot be sufficient for statistical analyses.
(???) hilip Lieberman argues that since band societies of approximately
(ERR) 0-50 people are bounded by nutritional limitations to what group
(SND) izes can be fed without at least rudimentary agriculture, big human
(???) rains consuming more nutrients than ape brains, group sizes of
(???) pproximately 150 cannot have been selected for in paleolithic humans.
(???) rains much smaller than human or even mammalian brains are also known
(???) o be able to support social relationships, including social insects
(???) ith hierarchies where each individual "knows" its place (such as the
(PNG) aper wasp with its societies of approximately 80 individuals) and
(???) omputer-simulated virtual autonomous agents with simple reaction
(PNG) rogramming emulating what is referred to in primatology as "ape
(PNG) olitics".
(???) omparisons of primate species show that what appears to be a link
(???) etween group size and brain size, and also what species do not fit
(SND) uch a correlation, is explainable by diet. Many primates that eat
(SND) pecialized diets that rely on scarce food have evolved small brains
(???) o conserve nutrients and are limited to living in small groups or
(???) ven alone, and they lower average brain size for solitary or small
(GIF) roup primates. Small-brained species of primate that are living in
(???) arge groups are successfully predicted by diet theory to be the
(SND) pecies that eat food that is abundant but not very nutritious. Along
(???) ith the existence of complex deception in small-brained primates in
(???) arge groups with the opportunity (both abundant food eaters in their
(???) atural environments and originally solitary species that adopted
(SND) ocial lifestyles under artificial food abundances), this is cited as
(???) vidence against the model of social groups selecting for large brains
(???) nd/or intelligence.
(???) Popularisation
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(???) Malcolm Gladwell discusses the Dunbar number in his 2000 book 'The
(TN3) ipping Point'. Gladwell describes the company W. L. Gore and
(???) ssociates, now known for the Gore-Tex brand. By trial and error, the
(???) eadership in the company discovered that if more than 150 employees
(???) ere working together in one building, different social problems could
(???) ccur. The company started building company buildings with a limit of
(DIR) 50 employees and only 150 parking spaces. When the parking spaces
(???) ere filled, the company would build another 150-employee building.
(???) ometimes these buildings would be placed only short distances apart.
(???) The number has been used in the study of virtual communities,
(???) specially MMORPGs, such as 'Ultima Online', and social networking
(???) ebsites, such as Facebook (Dunbar himself did a study on Facebook in
(PHO) 010) and MySpace.
(???) The Swedish Tax Agency planned to reorganise its functions in 2007
(???) ith a maximum 150 employees per office, referring to Dunbar's
(???) esearch.
(???) In 2007, Cracked.com editor David Wong wrote a humour piece titled
(???) What is the Monkeysphere?" explaining Dunbar's number and its
mplications. In his 2012 novel 'This Book Is Full of Spiders', the
(???) haracter Marconi explains to David the effect Dunbar's number has on
(HTM) uman society. In Marconi's explanation, the limit Dunbar's number
mposes on the individual explains phenomena such as racism and
(???) enophobia, as well as apathy towards the suffering of peoples outside
(???) f an individual's community.
(???) In a piece for the 'Financial Times' (10 August 2018) titled "Why
(DOC) rink is the secret to humanity's success", Dunbar mentioned two more
(???) umbers: an inner core of about 5 people to whom we devote about 40
(PNG) ercent of our available social time and 10 more people to whom we
(DOC) evote another 20 percent. All in all, we devote about two-thirds of
(???) ur time to just 15 people.
(???) In episode 103 of the podcast 'Hello Internet' (31 May 2018) Brady
(???) aran and CGP Grey discuss the reasons the number may be limited to
(DIR) 50, including the ability to keep track of political relationships in
(???) arge groups of people and the amount of time that people have to
(DOC) evote towards developing and maintaining friendships.
(???) See also
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(???) Size of groups, organizations, and communities
(???) External links
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(???)
(???) https://web.archive.org/web/20051211031726/http://www.liv.ac.uk/researchintelligence/issue17/brainteaser.html
(???) The ultimate brain teaser"] - an article on Dunbar's research at
(???) niversity of Liverpool Research Intelligence
(???) [http://www.lifewithalacrity.com/2004/03/the_dunbar_numb.html The
(???) unbar Number as a Limit to Group Sizes] by Christopher Allen -
(???) pplying Dunbar's number to on-line gaming, social software,
(???) ollaboration, trust, security, privacy, and internet tools, by
(???) hristopher Allen
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(???) https://web.archive.org/web/20141202004603/http://fora.tv/2010/02/18/Robin_Dunbar_How_Many_Friends_Does_One_Person_Need
(???) obin Dunbar: How Many Friends Does One Person Need?] Fora.TV talk at
(???) he RSA
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(???) riginal Article: http://en.wikipedia.org/wiki/Dunbar's_number