The word meme originated with Richard Dawkins’ 1976 book The Selfish Gene. Dawkins cites as inspiration the work of geneticist L. L. Cavalli-Sforza, anthropologist F. T. Cloak[16] and ethologist J. M. Cullen.[17] Dawkins wrote that evolution depended not on the particular chemical basis of genetics, but only on the existence of a self-replicating unit of transmission—in the case of biological evolution, the gene. For Dawkins, the meme exemplified another self-replicating unit with potential significance in explaining human behavior and cultural evolution. Although Dawkins invented the term ‘meme’ and developed meme theory, the possibility that ideas were subject to the same pressures of evolution as were biological attributes was discussed in Darwin’s time. T. H. Huxley claimed that ‘The struggle for existence holds as much in the intellectual as in the physical world. A theory is a species of thinking, and its right to exist is coextensive with its power of resisting extinction by its rivals.'[18]