As an evolutionary biologist, Richard Dawkins has broadened our understanding of the genetic origin of our species; as a popular author, he has helped lay readers understand complex scientific concepts. He's best-known for the ideas laid out in his landmark book The Selfish Gene and fleshed out in The Extended Phenotype: the rather radical notion that Darwinian selection happens not at the level of the individual, but at the level of our DNA. The implication: We evolved for only one purpose — to serve our genes. Of perhaps equal importance is Dawkins' concept of the meme, which he defines as a self-replicating unit of culture -- an idea, a chain letter, a catchy tune, an urban legend -- which is passed person-to-person, its longevity based on its ability to lodge in the brain and inspire transmission to others. Introduced in The Selfish Gene in 1976, the concept of memes has itself proven highly contagious, inspiring countless accounts and explanations of idea propagation in the information age.