My daughters will occasionally relate some bit of culture from their school, such as a joke or prank, that I recognize from my youth four decades ago. It is amazing to think that these memes have persisted in “kiddy culture” largely unchanged over decades, transmitted largely from older to younger children, though siblings or perhaps schoolmates. Of course, some of these memes were already old when I was a child. How far back do they go, I wonder?

Forget slightly crude jokes, what about classic fairy tales? Many of these tales were first recorded in the 19th century by the Brothers Grimm, but they were German academics who were just collecting folktales, not authoring them. Those folktales existed in oral tradition for a long time prior to being written down, but again, how long?

A recent study published in the Royal Society Open Science seeks to answer that question. The authors, Sara Graça da Silva and Jamshid J. Tehrani, took an evolutionary approach to the question.

They analyzed the language of different versions of folktales in different languages and cultures looking for statistical evidence that those versions shared a common ancestor through vertical, rather than horizontal, transmission. Vertical transmission means transmission from a parent to an offspring generation. Horizontal transmission would be from one culture over to another.

The idea is that if two cultures shared a folktale, and both cultures received that folktale only through vertical transmission, then the folktale must be at least as old and the last common ancestor between those two cultures. If those cultures split 3,000 years ago, then the folktale is older than 3,000 years. Of course, if the first culture exported the folktale to the second culture one hundred years ago, the analysis does not work.

How to distinguish vertical from horizontal transmission is the technical crux of the paper. Here is the technical description of the methods they used:

To test for signatures of vertical transmission, we measured how well the distribution of each tale could be accounted for by the populations’ linguistic relationships using Fritz and Purvis’ D statistic. D is a measure of phylogenetic signal that expresses the number of character changes in a binary trait on a tree scaled by two null distributions: one in which character states are randomly reshuffled among the tips of the tree, and one where the character evolves under a selectively neutral, Brownian model of evolution. A D of 0 indicates that the distribution of character states among the taxa is what would be expected for a neutral trait under a purely vertical mode of inheritance, while values approaching 1 approximate a phylogenetically random distribution.

I think this boils down to this – they analyzed the language in different versions of the folktale to see if they represented only random drift of details, under no selective pressure, which would be expected under pure vertical transmission. Meanwhile, a random shuffling of details could indicate horizontal transmission.

Using this method they weeded out tales that statistically matched a pattern of recent horizontal transfer, leaving 76 fairy tales that seem to have spread mainly through vertical transfer. They then did linguistic analysis to see how far back the stories would have to go in order to explain their distribution.

They found:

This approach allowed the researchers to trace certain tales, such as The Smith and the Devil, which tells the story of a blacksmith who makes a deal with the devil in exchange for unmatched smithing prowess, back thousands of years—all the way to the Proto-Indo-European people . If the analysis is correct, it would mean the oldest fairy tales still in circulation today are between 2500 and 6000 years old. Other stories seem to be much younger, appearing for the first time in more modern branches of the language tree.

That is very interesting, and not surprising. Good narratives have amazing cultural inertia. The findings do suggest the question of why some stories have survived for so long. It could just be random – an essentially random distribution of survival of ancient stories with a long tale containing a residue of a few stories that survived by chance alone. In other words, it could be down to mostly luck and chance.

It is interesting to speculate, however, about what features these stories might have that gave them such longevity. This study does not address that question, just suggests it for future research. But here is the speculation.

The authors feel it might come down to stories that have, “minimally counterintuitive narratives.” They are simple tales that are easy to understand and remember, but they have one supernatural element and one easy lesson.

I also think a huge factor is the degree to which stories resonate with basic human psychology. The ideas and emotions in the stories click comfortably into place within the common human psyche. To me, that is the most fascinating part of all this – what is it about human psychology that is drawn to these stories.

Alternatively, is it primarily cultural? Social scientists ask this question all the time – which ideas and behaviors are universal and which are cultural? If everyone culture does something, it is probably hardwired into the human brain. We can apply the same approach to narratives. I suspect there will be some common themes, but the details will be culturally driven. I also suspect that different cultures will emphasize different themes, representing their cultural character.

Conclusion

Stories are a huge part of how humans think and interface with each other and the world. Studying stories is therefore a huge window into human psychology and culture.

This latest study shows that some narrative can survive for thousands of years, through massive cultural and technological change. I look forward to seeing follow up research on this phenomenon to see what it can tell us about the human condition.