This American Life had a great segment introducing this: http://www.thisamericanlife.org/radio-archives/episode/491/tribes?act=2#play http://www.thisamericanlif

This American Life had a great segment introducing this: http://www.thisamericanlife.org/radio-archives/episode/491/tribes?act=2#play http://www.thisamericanlife.org/radio-archives/episode/491/t...