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Media & PsychologySocial Psychology

150 — Dunbar’s Number

The science of brains and relationships.

Jerry Silfwer
by Jerry Silfwer

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“150” is often referred to as Dunbar’s Number.

Dunbar’s num­ber has been observed in vari­ous aspects of human soci­ety. The group size sug­gests a cog­nit­ive lim­it for relationships.

The num­ber 150 emerged from stud­ies of social group sizes in vari­ous soci­et­ies, as well as in non-human prim­ates, and from the ratio of neo­cor­tic­al volume to the total brain size. 1Dunbar, R. I. M. (1992). Neocortex size as a con­straint on group size in prim­ates. Journal of Human Evolution, 22(6), 469 – 493.

For instance, mil­it­ary units have often been organ­ized around this size, and some busi­nesses have used it as a guide for struc­tur­ing their organizations.

Here we go:

Dunbar’s Number: 150 Relationships

Robin Dunbar - Social Group Sizes - The PR Blog - Doctor Spin
Robin Ian MacDonald Dunbar is a British anthro­po­lo­gist, evol­u­tion­ary psy­cho­lo­gist, and spe­cial­ist in prim­ate behaviour.
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150 — Dunbar’s Number

Robin Dunbar, a British anthro­po­lo­gist and evol­u­tion­ary psy­cho­lo­gist, pro­posed what’s known as “Dunbar’s Number” — a the­ory sug­gest­ing that humans can only com­fort­ably main­tain about 150 stable rela­tion­ships. 2Dunbar, R. I. M. (1998). The social brain hypo­thes­is. Evolutionary Anthropology: Issues, News, and Reviews, 6(5), 178 – 190.

This includes fam­ily, friends, col­leagues, and oth­ers with whom a per­son can keep mean­ing­ful con­tact. Beyond this num­ber, the qual­ity of rela­tion­ships can dimin­ish due to the lim­it­a­tions in our men­tal band­width. 3Silfwer, J. (2012, April 14). Social Group Sizes (The Social Brain Hypothesis). Doctor Spin | the PR Blog. https://​doc​tor​spin​.net/​g​r​o​u​p​-​s​i​z​es/

“Dunbar’s num­ber is a sug­ges­ted cog­nit­ive lim­it to the num­ber of people with whom one can main­tain stable social rela­tion­ships. […] No pre­cise value has been pro­posed for Dunbar’s num­ber. It has been pro­posed to lie between 100 and 230, with a com­monly used value of 150. Dunbar’s num­ber states the num­ber of people one knows and keeps social con­tact with, and it does not include the num­ber of people known per­son­ally with a ceased social rela­tion­ship, nor people just gen­er­ally known with a lack of per­sist­ent social rela­tion­ship, a num­ber which might be much high­er and likely depends on long-term memory size.”
Source: Wikipedia 4Dunbar’s num­ber. (2023, May 29). In Wikipedia. https://en.wikipedia.org/wiki/Dunbar%27s_number

According to Dunbar, this lim­it is a dir­ect func­tion of rel­at­ive neo­cor­tex size, which con­strains our abil­ity to keep track of com­plex social rela­tion­ships. 5It’s worth not­ing that the concept of Dunbar’s Number has been debated and scru­tin­ised with­in the sci­entif­ic com­munity.

Learn more: 150 — Dunbar’s Number

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Group Size Examples

The concept of Dunbar’s num­ber, around 150, has been observed in vari­ous social and organ­iz­a­tion­al contexts. 

Here are some examples:

  • Hutterites. The Hutterites are a com­mun­al branch of Anabaptists who, like the Amish and Mennonites, trace their roots to the Radical Reformation of the 16th cen­tury. They inten­tion­ally split their colon­ies once they grew bey­ond 150 mem­bers to ensure every­one with­in the com­munity knew each other.
  • Military units. Traditionally, the “Company,” a stand­ard unit in mil­it­ary organ­iz­a­tion, tends to hov­er around the Dunbar num­ber. For instance, the basic fight­ing unit in the Roman Army, the Century, was made up of 80 men, close to Dunbar’s number.
  • Businesses. Some mod­ern busi­nesses, such as the Gore-Tex com­pany (known for its innov­at­ive work cul­ture), lim­it the size of their offices to 150 employ­ees. This main­tains a more intim­ate, dir­ect, and effi­cient com­mu­nic­a­tion struc­ture among all office members.
  • Neolithic farm­ing vil­lages. Archaeological evid­ence sug­gests that many Neolithic farm­ing vil­lages had a pop­u­la­tion of 120 to 150 individuals.
  • Hunter-gather­er soci­et­ies: Anthropological research indic­ates that tra­di­tion­al hunter-gather­er soci­et­ies typ­ic­ally had a core group size of about 100 – 150 individuals.

These are only approx­im­ate val­ues; the actu­al “Dunbar’s Number” can vary from per­son to per­son or from con­text to con­text. However, they sug­gest a gen­er­al human propensity to form and main­tain stable social rela­tion­ships up to this number.

Typical Social Group Sizes

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Typical Social Group Sizes

How many social con­nec­tions you you com­fort­ably sus­tain? According to the social brain hypo­thes­is, lim­its exist. 6Zhou WX, Sornette D, Hill RA, Dunbar RI. Discrete hier­arch­ic­al organ­iz­a­tion of social group sizes. Proc Biol Sci. 2005 Feb 22;272(1561):439 – 44.

“The ‘social brain hypo­thes­is’ for the evol­u­tion of large brains in prim­ates has led to evid­ence for the coe­volu­tion of neo­cor­tic­al size and social group sizes, sug­gest­ing that there is a cog­nit­ive con­straint on group size that depends, in some way, on the volume of neur­al mater­i­al avail­able for pro­cessing and syn­thes­iz­ing inform­a­tion on social rela­tion­ships.”
Source: Proceedings of the Royal Society B: Biological Sciences 7Zhou, X., Sornette, D., Hill, R. A., & M. Dunbar, R. I. (2005). Discrete hier­arch­ic­al organ­iz­a­tion of social group sizes. Proceedings of the Royal Society B: Biological Sciences, 272(1561), … Continue read­ing

Scientific evid­ence sug­gests that people tend to organ­ise them­selves not in an even dis­tri­bu­tion of group sizes but in dis­crete hier­arch­ic­al social groups of more par­tic­u­lar sizes:

Alas, there seems to be a dis­crete stat­ist­ic­al order in the com­plex chaos of human relationships:

  • Support clique (3 – 5 people)
  • Sympathy group (12 – 20 people)
  • Band (30 – 50 people)
  • Clan (150 people)
  • Megaband (500 people)
  • Tribe (1,000 – 2,000 people)

“Such dis­crete scale invari­ance could be related to that iden­ti­fied in sig­na­tures of herd­ing beha­viour in fin­an­cial mar­kets and might reflect a hier­arch­ic­al pro­cessing of social near­ness by human brains.“
Source: Proceedings of the Royal Society B: Biological Sciences 8Zhou, X., Sornette, D., Hill, R. A., & M. Dunbar, R. I. (2005). Discrete hier­arch­ic­al organ­iz­a­tion of social group sizes. Proceedings of the Royal Society B: Biological Sciences, 272(1561), … Continue read­ing

Read also: Group Sizes (The Social Brain Hypothesis)

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ANNOTATIONS
ANNOTATIONS
1 Dunbar, R. I. M. (1992). Neocortex size as a con­straint on group size in prim­ates. Journal of Human Evolution, 22(6), 469 – 493.
2 Dunbar, R. I. M. (1998). The social brain hypo­thes­is. Evolutionary Anthropology: Issues, News, and Reviews, 6(5), 178 – 190.
3 Silfwer, J. (2012, April 14). Social Group Sizes (The Social Brain Hypothesis). Doctor Spin | the PR Blog. https://​doc​tor​spin​.net/​g​r​o​u​p​-​s​i​z​es/
4 Dunbar’s num­ber. (2023, May 29). In Wikipedia. https://en.wikipedia.org/wiki/Dunbar%27s_number
5 It’s worth not­ing that the concept of Dunbar’s Number has been debated and scru­tin­ised with­in the sci­entif­ic community.
6 Zhou WX, Sornette D, Hill RA, Dunbar RI. Discrete hier­arch­ic­al organ­iz­a­tion of social group sizes. Proc Biol Sci. 2005 Feb 22;272(1561):439 – 44.
7, 8 Zhou, X., Sornette, D., Hill, R. A., & M. Dunbar, R. I. (2005). Discrete hier­arch­ic­al organ­iz­a­tion of social group sizes. Proceedings of the Royal Society B: Biological Sciences, 272(1561), 439 – 444. https://​doi​.org/​1​0​.​1​0​9​8​/​r​s​p​b​.​2​0​0​4​.​2​970
Jerry Silfwer
Jerry Silfwerhttps://doctorspin.net/
Jerry Silfwer, alias Doctor Spin, is an awarded senior adviser specialising in public relations and digital strategy. Currently CEO at Spin Factory and KIX Communication Index. Before that, he worked at Kaufmann, Whispr Group, Springtime PR, and Spotlight PR. Based in Stockholm, Sweden.
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