Have you heard the story of the good sister and the bad sister? When they leave home, the good sister is kind to the people and animals she meets, and is rewarded in gold. The bad sister is haughty and greedy, and is rewarded with a box of snakes.

This folk tale has hundreds of variants, and it has been passed on across Europe for centuries. But how similar your version is to mine depends not just on how far apart we live but also on how ethnically and linguistically different our cultures are, according to a new study.

If folk tales simply spread by diffusion, like ink blots in paper, one would expect to see smooth gradients in these variations as a function of distance. Instead, researchers found that language differences between cultures create significant barriers to that diffusion.

These barriers are stronger than those for the exchange of genes — a message that might be crudely expressed as: “I’ll sleep with you, but I prefer my stories to yours.”

Cultural boundaries
In the study, a team of researchers in Australia and New Zealand used the statistical tools of population genetics to investigate variations in ‘The kind and the unkind girls’ across 31 European populations, such as Armenian, Scottish, Basque and Icelandic groups. Their results appear today in the Proceedings of the Royal Society B1.

Read more at Nature.