Robin Dunbar: We can have about 150 friends
This number is limited by the size of the neocortex area in the frontal lobe of our brain.
This does not only apply to people, as the size of animal groups is also surprisingly dependent on the size of the same brain area Maintaining relationships with other members of the species is a complicated matter that requires a lot of brain work.
The majority of people have 100–200 friends on Facebook. The impression that people usually have hundreds of friends is a myth that is not true. If there are more people in the networks, the relationships are not generally bi-directional in nature.
The same number comes up consistently in different materials. Studying the e-mails of researchers has also indicated that a person can usually carry out bi-directional e-mail traffic with approximately 100–200 other people. The activities of organisations generally become more difficult when the threshold of 150 people is exceeded.
Friends and acquaintances are divided into friends on different levels. The number of closest friends is usually approximately five. People usually give these friends some 40% of the time they spend with friends. The best ways of connecting people are laughter, discussion in small groups and singing.
Watch Dunbar's talk here.