The PR BlogMedia & PsychologyBehavioural PsychologySocial Group Sizes (The Social brain Hypothesis)

Social Group Sizes (The Social brain Hypothesis)

The science of in-groups in a wired world.

Cover photo: @jerrysilfwer

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?

Let’s take a closer look:

Dunbar’s Number

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

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.

150 — Dunbar’s Number

Most of you know Dunbar’s Number. It’s based on the idea that every one of us has lim­ited social bandwidth.

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

Read also: Group Sizes (From Support Cliques to Tribes)

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).

Typical Social Group Sizes

Have you ever heard of the social brain hypo­thes­is? 1Zhou WX, Sornette D, Hill RA, Dunbar RI. Discrete hier­arch­ic­al organ­iz­a­tion of social group sizes. Proc Biol Sci. 2005 Feb 22;272(1561):439 – 44. doi: 10.1098/rspb.2004.2970. PMID: 15734699; PMCID: … Continue read­ing

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: Discrete Hierarchical Organization of Social Group Sizes

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: Discrete Hierarchical Organization of Social Group Sizes

Read also: Group Sizes (From Support Cliques to Tribes)

It’s the sci­ence of in-groups in a wired world.

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:

How to scale social media marketing.
How we as indi­vidu­als shift between roles and communities.

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’s the amp­li­fic­a­tion of 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:

Group Sizes | Behavioural Psychology | Doctor Spin
We can sus­tain more extens­ive net­works as ties weaken.

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:

  • Inner core (3−5 people)
  • Semi-private lay­er (<150 people)
  • Superficial lay­er (>150 people)

The Engagement Pyramid

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.

When cre­at­ing a cam­paign, it’s essen­tial to cater to the inner circles, but don’t for­get the dif­fer­ent lay­ers of the engage­ment pyramid. 

The Engagement Pyramid

The 1% rule of online engage­ment was mainly an urb­an legend on the inter­net. Still, a peer-reviewed paper from 2014 entitled The 1% Rule in Four Digital Health Social Networks: An Observational Study con­firmed the 1% rule of thumb.

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 1−9−90 rule.

Read also: The Engagement Pyramid

1 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. doi: 10.1098/rspb.2004.2970. PMID: 15734699; PMCID: PMC1634986.
Jerry Silfwer
Jerry Silfwer
Jerry Silfwer, alias Doctor Spin, is an awarded senior adviser specialising in public relations and digital strategy. Currently CEO at KIX Index and Spin Factory. Before that, he worked at Kaufmann, Whispr Group, Springtime PR, and Spotlight PR. Based in Stockholm, Sweden.

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