Memetics is a theory of the evolution of culture based on Darwinian principles with the meme as the unit of culture. The term "meme" was coined by biologist Richard Dawkins in his 1976 book The Selfish Gene, to illustrate the principle that he later called "Universal Darwinism". All evolutionary processes depend on information being copied, varied, and selected, a process also known as variation with selective retention. The conveyor of the information being copied is known as the replicator, with the gene functioning as the replicator in biological evolution. Dawkins proposed that the same process drives cultural evolution, and he called this second replicator the "meme," citing examples such as musical tunes, catchphrases, fashions, and technologies. Like genes, memes are selfish replicators and have causal efficacy; in other words, their properties influence their chances of being copied and passed on. Some succeed because they are valuable or useful to their human hosts while others are more like viruses.
Just as genes can work together to form co-adapted gene complexes, so form groups of memes acting together co-adapted meme complexes or memeplexes. Memeplexes include (among many other things) languages, traditions, scientific theories, financial institutions, and religions. Dawkins famously referred to religions as "viruses of the mind".