150 — Dunbar’s Number

“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:

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

Group Size Examples

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

Here are some examples:

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.

Social Group Sizes (For Social Brains)

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:

“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)

THANKS FOR READING.
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