Social Group Sizes (The Social Brain Hypothesis)

Humans tend to organ­ise them­selves in stable group sizes.

What used to be dic­tated by phys­ic­al prox­im­ity is now com­pletely rid of any such restrictions. 

The inter­net allows us to find many dif­fer­ent types of tribes and many dif­fer­ent types of people to “include” in our groups.

Today, we live in a wired world where you can main­tain mean­ing­ful rela­tion­ships with indi­vidu­als without geo­graph­ic­al con­nec­tions. But how large can such groups be?

Here we go:

Dunbar’s Number

The most fam­ous group size is prob­ably Dunbar’s number:

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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. ¹Dunbar, 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. ²Silfwer, 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 ³Dunbar’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. ⁴It’s worth not­ing that the concept of Dunbar’s Number has been debated and scru­tin­ised with­in the sci­entif­ic com­munity.

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From Support Cliques to Tribes

But there are oth­er not­able group sizes apart from Dunbar’s num­ber. These stable group sizes range from sup­port cliques (3−5 people) to tribes (1,000−2,000 people).

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Typical Social Group Sizes

How many social con­nec­tions you you com­fort­ably sus­tain? According to the social brain hypo­thes­is, lim­its exist. ⁵Zhou 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 ⁶Zhou, 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 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

Read also: Group Sizes (The Social Brain Hypothesis)

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Online Identities and Interest Groups 

I would say I do know 150 people that I’ve spent time with over the years. 

But I also know 150 col­leagues that I’ve had. I also know 150 people from the pub­lic rela­tions industry, for sure. And I know at least 150 social media nat­ur­als, and so on. 

How does group form­a­tion scale in social media? 

I appre­ci­ate this mod­el by Viil Lid, PhD can­did­ate in Communication & Information Sciences at the University of Hawaii:

When I’m asked what makes the “social media revolu­tion” so spe­cial, I always say that nev­er before in human his­tory have we seen human groups form­ing at such speeds, almost inde­pend­ent of demo­graph­ic factors. 

It amp­li­fies Dunbar’s num­ber at the interest group level — not due to any sud­den increase in our cap­ab­il­ity to sus­tain more than 150 relationships.

Group Sizes of Sustainable Relationships

The effects of digit­al spread are likened to vir­al infec­tions because bound­ary span­ners and indi­vidu­al nodes have rela­tion­ships in sev­er­al dif­fer­ent types of interest networks. 

For each of these net­works, Liid once again shows us a mod­el that I’ve been using in sev­er­al of the sem­inars I’ve given:

How many “Dunbar, num­ber interest tribes” can a single indi­vidu­al main­tain? If we dig deep­er into this ques­tion, we must also determ­ine the strength of the indi­vidu­al bind­ings. Interestingly enough, we see Dunbar’s num­ber in action once again:

Building trust is a jour­ney from the peri­phery to the centre. You start any rela­tion­ship with an indi­vidu­al or a brand by being a stranger. 

PR pro­fes­sion­als should explore the digit­al space, not for clicks, memes, or vir­als but to build and main­tain rela­tion­ships using online social psy­cho­logy. Social media does­n’t scale lin­early, but tap­ping into dif­fer­ent and pre-exist­ing interest groups does.

The Engagement Pyramid

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The Engagement Pyramid

The 1% rule of online engage­ment was mainly an urb­an legend on the inter­net. However, a peer-reviewed paper from 2014 con­firmed the 1% rule of thumb. ⁸Trevor van Mierlo. (2014). The 1% Rule in Four Digital Health Social Networks: An Observational Study. Journal of Medical Internet Research, 16(2), e33 – e33. … Continue read­ing

Active pub­lics dis­trib­ute them­selves in a way proven sci­en­tific­ally by soci­olo­gists — long before the inter­net and social media emerged. 

The Engagement Pyramid divides pub­lics into three dis­tinct groups:

• Creators (1%)
• Contributors (9%)
• Lurkers (90%)

When study­ing inter­net for­ums spe­cific­ally, it’s not uncom­mon to find that 90% of users have nev­er pos­ted (lurk­ers), 9% are adding only to exist­ing top­ics and threads (con­trib­ut­ors), and 1% are act­ively start­ing new sub­jects and threads (cre­at­ors).

The Engagement Pyramid is some­times called the 1% rule or the 90−9−1 principle.

“The 90−9−1 prin­ciple and Zipf’s Law both effect­ively clas­si­fy mem­bers in online sup­port groups, with the Zipf dis­tri­bu­tion account­ing for 98.6% of the vari­ance.”
Source: Internet Interventions ⁹Carron-Arthur, B., Cunningham, J., & Griffiths, K. (2014). Describing the dis­tri­bu­tion of engage­ment in an Internet sup­port group by post fre­quency: A com­par­is­on of the 90−9−1 Principle and … Continue read­ing

Learn more: The Engagement Pyramid (The 90−9−1 Principle)

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PR Resource: Psychology

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Doctor Spin’s PR School: Free Psychology PR Course

Join this free Psychology PR Course to learn essen­tial skills tailored for pub­lic rela­tions pro­fes­sion­als. Start now and amp­li­fy your impact on soci­ety today.

• 58 Logical Fallacies and Cognitive Biases
• Social Group Sizes (The Social Brain Hypothesis)
• The Pitfalls of Groupthink: Decision-Making in Organisations
• Cognitive Dissonance: Mental Harmony Above All Else
• Survivorship Bias — Abraham Wald and the WWII Airplanes
• The Engagement Pyramid (The 90−9−1 Principle)
• 150 — Dunbar’s Number
• Theory of Mind: A Superpower for PR Professionals
• The Amplification Hypothesis: Counter Extreme Arguments
• The Baader-Meinhof Phenomenon: Heard About It Before?
• The Halo Effect: Why Attractiveness Matters in PR
• The Paradox of Prominence
• Parkinson’s Law & The Law of Triviality (Bike Shed Effect)
• Diffusion of Innovations

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