Primates are animals that form stable, social groups and the size of these groups is thought to have a direct relation to the size of the neocortex of the species concerned. In the 1990s the British anthropologist Robin Dunbar argued that the size of the human neocortex should enable us to maintain cohesive social groups of around 150 members. This became known as ‘Dunbar’s number’.
To maintain this size, human groups would need a clear incentive to remain together and would need to devote a good proportion of their time to some form of social grooming. However, according to Dunbar  a common language obviates the need for regular physical intimacy and allows social groups to remain cohesive through such instruments as gossip, story-telling and so on.
Certain companies have discovered that social problems begin when more than 150 people are working in the same building. W.L. Gore and Associates famously designed all their buildings with a capacity for 150 employees.
What about the language teaching business? Does Dunbar’s number have any validity here? Some of the evidence suggests that it does:
How many Accredited Members does EAQUALS currently have? According to their website the answer is 141.
What about IALC? According to their website, they have 161 members, although that number may include some temporary summer centres.
Also, coincidentally or not, the International House World Organisation has had around 150 affiliate members for as long as anyone can remember. New affiliates join, others leave, but the total remains more or less the same.
At the latest IHWO conference in Catania, Italy, I suggested that we should try to disprove that we are being held back by the size of our neocortex and actively recruit enough new affiliates to push the net total up to 170. Of course if we succeed, we may be risking the social cohesion of the organisation. But perhaps the neocortex of IH affiliates will demonstrate its ability to cope.
If you would like more information on how to become an affiliate of IHWO you can click here: https://ihworld.com/join-ih/
Or you can write to me at firstname.lastname@example.org 6�
 Grooming, Gossip and the Evolution of Language – Harvard University Press, 1996