Dawkins cites as inspiration the work of geneticist L. L. Cavalli-Sforza, anthropologist F. T. Cloak, and ethologist J. M. Cullen. 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.
"Kilroy was here" was a graffito that became popular in the 1940s, and existed under various names in different countries, illustrating how a meme can be modified through replication. This is seen as one of the first widespread memes in the world
Dawkins used the term to refer to any cultural entity that an observer might consider a replicator. He hypothesized that one could view many cultural entities as replicators, and pointed to melodies, fashions and learned skills as examples. Memes generally replicate through exposure to humans, who have evolved as efficient copiers of information and behavior. Because humans do not always copy memes perfectly, and because they may refine, combine or otherwise modify them with other memes to create new memes, they can change over time. Dawkins likened the process by which memes survive and change through the evolution of culture to the natural selection of genes in biological evolution.
Dawkins defined the meme as a unit of cultural transmission, or a unit of imitation and replication, but later definitions would vary. The lack of a consistent, rigorous, and precise understanding of what typically makes up one unit of cultural transmission remains a problem in debates about memetics. In contrast, the concept of genetics gained concrete evidence with the discovery of the biological functions of DNA. Meme transmission requires a physical medium, such as photons, sound waves, touch, taste, or smell because memes can be transmitted only through the senses.