The Dunbar number is a measure of the cognitive limit to the number of individuals with whom a person can maintain stable relationships. The concept has intrigued sociologists and anthropologists since it was first recognized as the correlation between brain capacity and group size in primates. In this talk, social software observer Christopher Allen discusses the interesting implications the Dunbar number theory has for the gathering of humans on line in the digital age.

The number of social groups a primate can track appears to be limited by the volume of the neocortex. This observation led British primatologist Robin Dunbar to suggest that there is a species-specific index of social group size, with humans falling about midway in the range. Since then, the concept of a biological basis for effective social group size has been taken up by pundits and business observers, most notably Malcolm Gladwell in The Tipping Point. Popularization has obscured some subtleties which Allen engages in his exploration of internet communitiies and social software. He compares the factors favoring small, medium and large groupings, and the interplay between people and software on the web in the form of games, blogs, wikis and chat.

On line games such as Ultima On-line and World of Warcraft provide massive amounts of data for measuring the gathering and communication of humans for various purposes. Through social network analysis, Allen hypothesizes that different group sizes impact a group's behavior and their choice of processes and tools. Three nodal sizes emerge, each with pros and cons. Small groups form easily, but are in danger of group-think and echo chamber effects. Larger groups are noisier and require a lot of time and energy in order to maintain reputations and social trust.

Designers of social software have not always been aware of the Dunbar number, yet some tools have hit the sweet spot for intimate or large scale group formation. Allen closes with an interesting comparison of features seen in blogs, wikis and sites such as Slashdot, LiveJournal and MySpace.