Social Network Layers

What it is

An innermost group of one or two people, then a support group, then a sympathy group, then a wider set. The structure is the part of Dunbar's account that was never derived from primate brains, which means it could be tested directly on people, and was.

In effect

Dunbar with Valerio Arnaboldi, Marco Conti and Andrea Passarella used the frequency of posts running in both directions to define real relationships, across two Facebook datasets and a Twitter dataset covering more than 185,000 people. Four layers appeared in the Facebook data and five in the Twitter data, with sizes and contact frequencies closely matching offline face-to-face networks, plus an innermost layer at about one and a half people that had previously only been hypothesised.

Layer sizes vary between people. Thomas Pollet, Sam Roberts and Dunbar found extraverts with larger networks at every layer, with associations modest in size.

What it does not say

It does not say the layers are cognitive furniture. Clustering a smoothly decaying distribution of contact frequencies will tend to produce discrete-looking groups whether or not any exist, and measuring humans instead of primates does not answer that objection.

It also does not rescue any specific figure by itself. What it does is put the outermost layer at roughly the familiar number by a route that has nothing to do with neocortex ratios.

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