We often think of communities as organic creatures, which come into existence and grow on their own. However, the truth is they are fragile blossoms. Although many communities surely germinate and bloom on their own, purposefully creating communities can take a tremendous amount of hard work, and one factor their success ultimately depends upon is their numbers. If a community is too small you'll often have insufficient critical mass to sustain it.

Last May I did an abbreviated version of my Dunbar Number talk at MeshForum 2006. A MP3 podcast of that talk is now available at IT Conversations  or can be downloaded here (10mb). If you'd like to follow along, here is a pdf copy of my presentation sides (10mb). Biggest addition to what I've written about before is some discussion about different kinds of social software and what what size groups they seem to be appropriate for.

Lately I've been noticing the spread of a meme regarding "Dunbar's Number" of 150 that I believe is misunderstanding of his ideas. The Science of Dunbar's Number Dunbar is an anthropologist at the University College of London, who wrote a paper on Co-Evolution Of Neocortex Size, Group Size And Language In Humans where he hypothesizes: ... there is a cognitive limit to the number of individuals with whom any one person can maintain stable relationships, that this limit is a direct function of relative neocortex size, and that this in turn limits group size .