Robin Dunbar: Social Brain Hypothesis (SBH)

Social networks seem to suggest that suddenly due to the internet we can have many friends; more friends means more support. Research suggests the opposite.

Anthropologist Robin Dunbar’s Social Brain Hypothesis (SBH) establishes a “quantitative relationship between group size and brain size”. In other words, our cognitive architecture (brain, body, heart, pores, etc…) limits the number of deep friendships (3-15 people) we can develop simultaneously. We are evolutionary creatures adapted for small clusters (villages of 150-200) immersed in an augmented networked situation.

In 1996, Dunbar wrote an excellent readable book Grooming Gossip and the Evolution of Language which argued that human language was actually a tool for power dynamics between tribe members, thus an aspect of social hierarchy; and that human community sizes are regulated by neocortex size. In 2016 his recently-published research concerns friendships in the era of Facebook; his results confirm his contention that:

…there is a cognitive constraint on the size of social networks that even the communication advantages of online media are unable to overcome…

This limit is thought to arise from a combination of a cognitive constraint (the product of the relationship with neocortex size known as the social brain hypothesis (SBH) [18,23]) and a time constraint associated with the costs of servicing relationships [24,25].

Who would support you in crisis? For many years sociologists have referred to a core support group as a grief/bereavement network; it follows a network typology/topology (which means it has the shape and form of a physical network and obeys similar dynamics). Dunbar distinguishes between “support clique (friends on whom you would depend for emotional/social support in times of crisis) and sympathy group (close friends).” Average is 4.1 for support clique and 13.6 for sympathy group. Dunbar’s research also finds that women have more friends than men, young people have more online friends, and teenagers have much smaller offline communities than adults.

His primary conclusion:

We can only interact coherently with a very small number of other people (about three, in fact) at any one time [40,41]. It seems that even in an online environment, the focus of our attention is still limited in this way.


Dunbar, Prof. Robin. 1997. Grooming, Gossip, and the Evolution of Language. Harvard University Press.

Dunbar, R. I. M. 2009. “The Social Brain Hypothesis and Its Implications for Social Evolution.” Annals of Human Biology 36 (5): 562–72. doi:10.1080/03014460902960289. http://rsos.royalsocietypublishing.org/content/3/1/150292

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