From biology to culture to the new new economy, the buzzword on everyone's lips is 'meme.' How do animals learn things? How does human culture evolve? How does viral marketing work? The answer to these disparate questions and even to what is the nature of thought itself is, simply, the meme. For decades researchers have been convinced that memes were The Next Big Thing for the understanding of society and ourselves. But no one has so far been able to define what they are. Until now. Here, for the first time, Robert Aunger outlines what a meme physically is, how memes originated, how they developed, and how they have made our brains into their survival systems. They are thoughts. They are parasites. They are in control. A meme is a distinct pattern of electrical charges in a node in our brains that reproduces a thousand times faster than a bacterium. Memes have found ways to leap from one brain to another. A number of them are being replicated in your brain as you read this paragraph.