In the last edition of John Brockman's always-provoctaive EDGE, Harvard MD and sociologist Nicholas Christakis talked about social networks. But instead of delving into well-trodden social network phenomena like viral videos, Christakis studies a variety of unexpected things that can spread through social networks, such as obesity, happiness, altruism, and, oddly, the taste for privacy. From the essay:
For me, social networks are like the eye. They are incredibly complex and beautiful, and looking at them begs the question of why they exist, and why they come to pass. Do we need a kind of just-so story to explain them? Do they just happen to be there, for no particular reason? Or do they serve some purpose — some ontological and also pragmatic purpose?
Along with my collaborator James Fowler, I have been wrestling with the questions of where social networks come from, what purpose they serve, what rules they follow, and what they mean for our lives. The amazing thing about social networks, unlike other networks that are almost as interesting — networks of neurons or genes or stars or computers or all kinds of other things one can imagine — is that the nodes of a social network — the entities, the components — are themselves sentient, acting individuals who can respond to the network and actually form it themselves. Link 
As EDGE is a conversation, the new edition includes two insightful responses to Christakis's essay, from Douglas Rushkoff and Alan Alda (yes, that Alan Alda), and, finally, Christakis's response to them. Also in this EDGE edition, photos  from the annual EDGE Dinner where big thinkers meet, eat, and somehow avoid being suffocated by the massive amount of smarts in the room. Link