Most people have heard of the 'six degrees of separation' theory, in which Stanley Milgram seemingly discovered that everyone is only six handshakes away from everyone else on the globe. What is even more astonishing is that other scientists have turned up profoundly similar structures to this social network in everything ranging from the world wide web to the food webs of any ecosystem, business links of any economy, connected neurons in the brain, and the network of interacting molecules in the human cell.