It has been claimed, notably by Dawkins and Dennett, that there are units of cultural evolution, called ‘memes’, whose survival is explicable in terms of Darwin's theory of evolution by natural selection. They also play an important part in Dennett's theory of consciousness. Memes are distinct memorable units, not atoms, which have vehicles, and whose success depends on the ability of those vehicles to multiply. We argue that even if the theory of memes is structurally isomorphic with the theory of natural selection, it has a very different ontology calling for novel accounts of variation, replication and fitness. We question whether such accounts are plausible, and conclude that memes and their tokenings cannot assume the causal roles they would have to to obey the ‘laws’ of the theory of evolution by natural selection.