Sunday, March 08, 2009

The Dunbar Number and Limits of Our Social Networks

THE SOCIAL MEDIA AND WEB 2.0 (though both are considered synonymous by some) provided the netizens with amazing new possibilities, like a new universe opening up with everyone mingling with everyone else. While the web (no pun intended) of these collaboration network, social in nature, kept increasing in complexity and continued expanding, there was no measure for if it were to follow the same yo-yo model of the actual Universe (try here). In other words, it was very difficult to ascertain if the motion was inward or outward, for there were no clear boundaries defined or known.
The size of the neocortex of the brain allows humans to have stable networks of about 150. This is known as "the Dunbar number".
With the help of Dr. Robin Dunbar’s research, perhaps we now have the first indications toward the limitations of Web 2.0 vis-a-vis human psychology and behaviour. Dr. Dunbar is an anthropologist currently with the Oxford University and has studied primates and humans and their social behaviour.

Many of the activities and exchanges on the online social networks are considered "grooming". In the wild, grooming is time-consuming: keeping track of who to groom —and why— demands quite a bit of mental computation. One needs to remember who is allied with, hostile to, or lusts after whom, and act accordingly.

On the web, social 'networking' algorithms and computations power help with these calculations. Yet, the cognitive power of the human brain limits the size of the social network that an individual of any given species can develop. Dr. Dunbar suggested that the size of the neocortex of the human brain allows for having stable networks of about 148 connections (or 150 in round figures). This is known as "the Dunbar number", and recent sampling of Facebook users network gives an average of about 120, which seems consistent with this hypothesis. The research continues further as follows:

Many institutions, from Neolithic villages to the maniples of the Roman army, seem to be organised around the Dunbar number.

[In the modern era] An average man —one with 120 friends— generally responds to the postings of only seven of those friends by leaving comments on the posting individual's photos, status messages or "wall". An average woman is slightly more sociable, responding to ten. When it comes to two-way communication such as e-mails or chats, the average man interacts with only four people and the average woman with six. Among those Facebook users with 500 friends, these numbers are somewhat higher, but not hugely so. Men leave comments for 17 friends, women for 26. Men communicate with ten, women with 16.

Humans may be advertising themselves more efficiently. But they still have the same small circles of intimacy as ever.
This also goes on to say that if you are "in touch" with that person fairly regularly with whom you are perhaps yet to work out a one-on-one, you are better off treasuring those interactions, for you have gotten into the "core" within the Dunbar circle. At the same time, in his 2005 book —The Human Story— Dunbar quotes Bob Marley's Redemption Song (try here), suggesting not to fall pray to the omnipresent temptations of 'grooming'.

(More to read and write on the Attention Economy in the coming posts.)
  • See also:
  • Go here for the relevant research paper [PDF] by Dr. Dunbar titled "The Social Brain Hypothesis" at the University of Liverpool website
  • Go here for The Economist article: "The size of social network".
  • Go here for a video lecture by Dr. Dunbar titled "What Makes Us Human?" at


  1. Very intereting !
    Surely it makes a lot of sense!

  2. Something that rings the "true" bell about it, isn't it?

    It appears however that the Dunbar Number for the "offline" social network of real life (for a neutral-overt) would be even smaller than 150, don't you think?

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