The evoluation of social media as captured by http://marketing.wtwhmedia.com from 1970 to 2009.
Compare that to a more comprehensive graphic by copyblogger
No doubt the evolution of social media sites is not just interesting, but it has also showed how human needs for online socialization has given birth to very specific platforms that addresses either professional or social needs of people. As much as human needs for online socialization is growing, and various platforms are needed to meet this need, not all platforms have succeeded in appealing to consumers' taste for online socialization. Moreover, the competition is so high that some have to drop. Below are some of the platforms that are no longer existing.
Avatars United, Bahu, Bolt, Capazoo, Ecademy, eConozco, FitFinder, Formspring, Hyves, Mugshot, PlanetAll, Pownce, Regeit, Sixdegrees.com, Surfbook, Windows Live Spaces, Yahoo! 360°, Yahoo! Kickstart, IslamTag, Yahoo! Mash, Friendster