Ideas are rarely solitary events. They don’t behave like so many bricks laid down in orderly rows - more like spores tossed into the air, catching on wind currents, landing where they will. Sometimes they germinate. Sometimes they rot. Richard Dawkins gave us the term "meme" in 1976 to describe the smallest unit of cultural transmission, analogous to the gene. Since then, we've struggled to find the right metaphor to explain the erratic, unpredictable, wildly nonlinear dynamics of idea propag...