With The Selfish Gene , Dawkins offered scientists a conceptual bridge between the reductionist imperatives of molecular biology and the taxonomies of zoology, psychology, and sociology. In other words, the metaphor of the selfish gene not only created an important context to explain human and animal behavior - it also created a framework for molecular biologists to examine the organic interactions of genes. The metaphor scaled from double helices to human interactions. But looking at the richness and complexity of life on Earth, Dawkins freely acknowledged that an ethology of the gene alone was simply not robust enough to explain evolution. So he applied a Darwinian view of culture, as well.
Memes are to cultural inheritance what genes are to biological heredity.
A meme for, say, astrology, could parasitize a mind just as surely as a hookworm could infest someone's bowels. They, too, are operated on by natural selection. Human evolution, Dawkins postulates, is a function of a co-evolution between genes and memes. Even that was not enough. Dawkins's intellectual adventure went well beyond the ethology of genes and memes to explore an even more radical insight into the nature of evolutionary dynamics.