Robin Dunbar on his Number
Video via http://www.youtube.com/watch?v=ppLFce5uZ3I&feature=player_embedded
Description
"humans have only a finite capacity for maintaining emotional relationships. There have been quite a few studies on this, from those looking at the average size of tribes, to those looking at networks of schoolchildren. Out of these, a value has emerged, called the Dunbar Number. Named for Robin Dunbar, a british anthropologist who investigated this number using a tribal survey technique, the Dunbar number is approximately 150 (though he points out that this statistic has a 95% confidence interval between 100 and 230). This number describes the historical tendency of human tribes to form up in groups of around 150 people. He asserts that this tendency is a reflection of some innate limitation of the emotional part of our brains -- which after all, are finite." (http://www.humblefacture.com/2010/10/importance-of-human-scale.html)