The Dunbar Constant is named for anthropologist Robin Dunbar, who wrote the book Grooming, Gossip and the Evolution of Language. He theorizes that 150 is the upper range of people any one person can personally maintain relationships with.
The term came up when Ross compared groupware to social software:
A fascinating article - now I need to read Dunbar's book!...these tools have the ability to support social scale that groupware could not. Most of the prior generations had decreasing returns to scale at about 150 users. With wikipedia you have milions trusting one another, creating a common resource, and a core community that has formed to steward collaborative intelligence (differs from collective intelligence).
