There are two points about this paper that are just fantastic.
First, Dr. Tehrani applies phylogenetic methods to identify both inheritance and diffusion processes. To accomplish this, he supplements his phylogenetic analysis with some network algorithms (neighbornet) and with detailed ethnographic knowledge of these fairy tale variants. The results are a wonderful illustration of how applying phylogenetic methods does not lock the researcher into the assumption that culture evolves by inheritance rather than by diffusion. Instead, the phylogenetic results actively support a reasonable ethnographic argument that cultural diffusion of the story elements was extensive in China, while the story elements were conserved and thus inherited in Europe. Papers like Dr. Tehrani’s move us well beyond the now sterile debate about whether culture is inherited or diffused (folks, sometimes it’s one, and sometimes it’s the other, and sometimes it’s a mix, so deal with it). I think studies like this one are a clear model for the future growth of quantitative cross-cultural analysis.
I would also point out a prior paper by Dr. Tehrani, myself, and others, that showed how phylogenetic methods could also detect other types of cultural diffusion – specifically when different functionally or socially linked blocks of cultural traits move together from one population to another.
To understand the basic point of this paper, think of the way new languages or religions can be adopted wholesale by a population, whether by choice or conquest. Such events result in cultural diffusion from the viewpoint of the population of people (they adopted a new set of traits) but from the viewpoint of the cultural elements the process is one of inheritance of a ‘cultural core’ because conversion can occur without blending of the elements within the core, i.e. the story elements of a single fairly tale, or the ritual elements of a religious denomination. This is why whole populations can be converted and languages or religions moved about across the globe, and yet the process of change in characteristics of these same languages or religions can still, at least sometimes, evolve through tree like inheritance. Our paper provides a method to detect and model such circumstances.
The second fantastic point about Dr. Tehrani’s paper is it shows the power of phylogenetic and network methods to construct empirically rigorous but quantitative models for global-scale cultural phenomenon. In the past I have often thought of language and religion as the two systems of human culture that are ubiquitous, variable, and ancient, but Dr. Tehrani’s paper makes a strong case that traditions of folklore and fairy tale may also fit these criteria. With the analytical methods we now have available, it is just a matter of motivation and funding for all of us to have quantitative global maps of the lineages (inheritance pathways) and linkages (diffusion pathways) among languages, religions, and folktales. Indeed, it is just such a quantified and global model of the landscape of human culture that I believe was the original, pre-Boasian, mandate of anthropology.