Just as biological evolution can be affected, not only by competition at the level of interactors, natural selection, and also competition for the most effective reproduction at the level of replicators, for example molecular or mutation drive, cultural evolution can also be very greatly affected by memetic drives, i.e. deterministic processes occurring at the level of replicators – e.g. at the level of a spoken language. The development of an orally transmitted story depends not only on how much the versions are liked by the individual story tellers and listeners and the probability with which they will pass on a particular variant, but also by the words that occur in the story and the errors occurring in the transmission of the story as a consequence of acoustic similarity of the words employed. Words that are difficult to pronounce or little known can, for example, be frequently replaced by other words, which can gradually change even the content of the story or song (Dawkins 1976).