Systems & complexity

Can online social media overcome the cognitive constraint on the size of social networks?

The social brain hypothesis1 suggests that there is a characteristic size for human social networks. This is around 150 people, and called “Dunbar’s Number” after social brain hypothesis researcher Robin Dunbar, Professor of Evolutionary Psychology at University of Oxford.

The internet has revolutionised our social world, allowing us to meet new people more efficiently and from a much wider area than is possible through face-to-face communication. But has this online social networking enabled us to overcome Dunbar’s Number?

Robin Dunbar puts this to the test in a new study2:

This study tests the claim that online social environments allow us to significantly increase the size of our social networks using two large structured random samples of the UK population and the number of friends listed on Facebook as the test metric. These data constitute the first attempt to determine the natural limit on network size using unbiased, randomized, stratified sampling of a national population. As such, this study is the first real attempt to test whether online social media do allow us to increase the size of our social networks.

The data collected has enabled the drawing of two conclusions:

First, they confirm, using two separate, large, nationally stratified random samples, that the typical egocentric network size for adult humans is similar to that predicted by the SBH [social brain hypothesis].

The second main finding is that the two samples provide a direct test of whether online SNSs [internet-based social networking sites] allow individuals to have larger social networks than is possible offline because SNSs allow one or more of the constraints that limit offline social network size to be circumvented. The results clearly suggest that they do not.

The study concludes with these observations:

The fact that people do not seem to use social media to increase the size of their social circles suggests that social media may function mainly to prevent friendships decaying over time in the absence of opportunities for face-to-face contact. Given that people generally find interactions via digital media (including the phone as well as instant messaging and other text-based social media) less satisfying than face-to-face interactions, it may be that face-to-face meetings are required from time to time to prevent friendships, in particular, sliding down through the network layers and eventually slipping over the edge of the 150 layer into the category of acquaintances (the 500 layer) beyond. Friendships, in particular, have a natural decay rate in the absence of contact, and social media may well function to slow down the rate of decay. However, that alone may not be sufficient to prevent friendships eventually dying naturally if they are not occasionally reinforced by face-to-face interaction.


  1. Dunbar, R.I.M. (1998). The social brain hypothesis. Evolutionary Anthropology, 6, 178–190.
  2. Dunbar, R. I. M. (2016). Do online social media cut through the constraints that limit the size of offline social networks? Royal Society Open Science, 3, .
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Bruce Boyes

Bruce Boyes ( is a knowledge management (KM), environmental management, and education professional with over 30 years of experience in Australia and China. His work has received high-level acclaim and been recognised through a number of significant awards. He is currently a PhD candidate in the Knowledge, Technology and Innovation Group at Wageningen University and Research, and holds a Master of Environmental Management with Distinction. He is also the editor, lead writer, and a director of the award-winning RealKM Magazine (, and teaches in the Beijing Foreign Studies University (BFSU) Certified High-school Program (CHP).

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