A new study supports the old theory that the human social circle is divided into layers, each with different numbers and categories of people. Their paper is available online here.
Researchers from University of Oxford, UK, and the Aalto University School of Science, Finland, put their brains together to understand human behaviour pertaining to their social circle. As per the social brain hypothesis, humans will have around 150 relationships at any one time which fit into different layers of the circle. The closest layer (characterising relationships with the most emotional closeness) will have fewer people, while the further the layer is, the more people it will accommodate.
With this aim in mind, the team, led by Robin Dunbar, went through cell phone records to spot the layers of friends as per the number of times the person has interacted with so and so on the phone.
The researchers analysed the call frequency, and with the help of clustering algorithms, they were able to categorise the call frequency into clusters. They were thus able to compare each cluster with the layer size. Their results show that the occurrence of the layers is indeed real, as they tally with their hypothesis.
The team had initially theorised that there were 4 layers which would cumulatively have 5, 15, 50, and 150 individuals respectively. The findings are very close to this trend: the average number of people in the layers based on the call frequency were 4.1, 11, 29.8, and 128.9. The apparent discrepancy with the hypothesised figures would be the result of natural variation, suggest the team. Others would deviate from this trend, though. Dunbar write that individuals who are clearly extroverts or introverts might be having an extra layer.
It is to be noted that phone calls not falling into the social circle category were not included; for instance, business calls were disregarded as well as other casual phone calls that had nothing to do with maintaining social contact.