Walnut forests walking along the Silk Road
If forests spread naturally, scientists would expect that genetic relatedness would spread in more concentric patterns. But Woeste said walnut genetics are related in long bands that spread east and west. For example, Woeste says walnuts in eastern Iran are closely related to walnuts in the Himalayas. That suggests to him that traders were carrying walnuts along the Silk Roads. And those traders had likely been keeping walnuts from the best trees, selecting for genes that gave the trees desired characteristics for nuts and wood. "Humans are always narrowing down genetic diversity to obtain a usable and more valuable crop," Woeste said. Much like crops evolve, languages also change over time. For instance, Spanish, French and Italian are considered Romance languages, having evolved from Latin. As populations split from each other, their languages changed, making those new languages children of the original. Having noticed the similarities in the word for "walnut" among several languages, Woeste and his colleagues grouped the languages currently spoken from the places where they sampled walnuts and traced the languages back to their ancestors. They found that the evolution of languages overlapped with the spread of walnut genetics. The authors of the study, published by the review pubblicata dalla rivista PLOS ONE, believe this shows that as people moved along the Silk Roads and traded, they specifically selected walnuts and traded them along their routes. Instead of having just a few domestic trees, those who obtained walnuts likely put effort into creating walnut forests that could be used for food and wood. "The factors that contribute to language being dispersed in Asia are the same as the way walnuts were dispersed," Woeste said. "It was the unique characteristics of walnut being useful for its wood and nuts that encouraged people to transport it, use it and then plant it as a forest as a long-term investment."