Under conditions where the exchange of information is largely unrestricted, one measure of a story or genre’s popularity is its pervasiveness, which may be assessed cross-culturally (e.g., how widespread the story is across societies) or intra-culturally (e.g., the percentage of group members who know the story). This definition embraces a host of motivations for telling or listening to a story (e.g., instruction, manipulation, curiosity, entertainment), many of which are subsumed by the criterion of relevance: when people have an interest in telling and/or listening to a given story, we may say that the story has relevance for them. Story relevance is likely rooted in local ecology: stories that address problems the audience may experience in real life may be expected to attract widespread interest because the information they contain is potentially useful. Conversely, stories that do not address such problems may attract less interest because they have no practical application. This essay develops the hypothesis that relevance affects story pervasiveness by examining two popular story genres from two very different socio-economic systems: the transformer tale and the bedtime story. The former is widespread across forager groups but absent in modern industrialized societies, while the latter is widespread across modern societies but glaringly absent from forager oral tradition. The principle of relevance would predict that each story addresses a problem that is specific to the ecology in which it is current. As we will see, this is the case: the problem addressed by the transformer is absent from modern industrialized societies, and the problem addressed by the bedtime story is absent from forager societies.