In folklore, this game is not only played vertically across generations, but horizontally across space as tales spread from society to society, with some—like Little Red Riding Hood—spreading globally. Over time, these so-called “international tale types” evolve into locally distinctive forms (known as oikotypes) as they adapt to different cultural and ecological contexts. This process is directly analogous to the emergence of new species in biological evolution and, I argue, can be studied using the same kinds of tools.

The idea is to use a biologist’s tool, like phylogenetic analysis which looks at genetic relationships among species, to investigate the evolution of folktales. This is because folktales not only evolve through similar processes as biological species (variation, selection and inheritance), but the problems of reconstructing them are also comparable. Just as the fossil record bears witness to a tiny proportion of extinct ancestral species, the literary record provides scarce textual evidence about early forms of folktales because they have been mainly transmitted through oral means. Phylogenetics can fill these gaps by using information about the past that has been preserved through the mechanism of inheritance.

Take the example of the long-running debate about the relationship between Little Red Riding Hood and similar tales from other regions of the world. These include East Asian tales in which a group of sisters are home alone when they hear a knock at the door. It is a tiger (or leopard, or some other predator) disguised as their grandmother. Despite her suspicious appearance (“Granny, why are your eyes so big?!”) they let her in. That night they share a bed, and the tiger eats the youngest girl to the horror of her sisters, who manage to escape.

Another tale, from central and southern Africa, involves a young girl who is tricked by an ogre pretending to be her brother. When her brother finds out he tracks down the ogre, kills him and cuts her out of the villain’s belly. Both these tales bear a clear resemblance to Little Red Riding Hood. But they are also similar to another well-known international type tale: “The Wolf and the Kids”, in which a group of goat kids are devoured by a wolf who gets into their house by impersonating their mother.

By analyzing variables in the plots and characters of 58 folktales using three methods of phylogenetic analysis, I was able to establish, in a paper just published in PLOS ONE, that the African tales are clearly more closely related to “The Wolf and the Kids” than they are to Little Red Riding Hood. The East Asian tales evolved by blending together elements from both these tales and from local folktales.

Previous writers have suggested, based on resemblances, that the East Asian tales were the source of the Western tales. My findings turn that theory on its head, suggesting that the Asian tales are in fact derived from a Western source, not vice versa. The kind of approach I have used promises new insights into the origins and relationships among story-telling traditions from different countries around the world. But ultimately I believe it can deliver more than that.