In recent years, Dunbar has taken his idea further by taking into account the emotional closeness between individuals. This has led him to the idea of Dunbar layers: that an individual’s group of 150 contacts is layered according to the strength of emotional ties.

Individuals, he says, generally have up to five people in the closest layer. The next closest layer contains an additional 10, the one beyond that an extra 35, and the final group another 100. So cumulatively, the layers contain five, 15, 50, and 150 people.