Sweet Potato Genes Say Polynesians, Not Europeans, Spread the Tubers Across the Pacific

Sweet potato samples preserved in centuries-old herbariums indicate that Polynesian sailors introduced the yam across Southeast Asia and the Pacific

Peruvians first domesticated the sweet potato around 8,000 years ago. And though the crop spread from there, the means by which it traveled have always remained contentious. One possibility was that Polynesian sailors first brought it home from across the ocean: The oldest carbonized sweet potato evidence in the Pacific hails back to about 1,000 A.D.—500 years before Columbus sailed to the Americas. The Polynesian word for sweet potato resembles the central Andes’ Quechua people’s word for the vegetable, too.

But the Polynesian sailor scenario was always just a hunch. Studying the plant’s genetic lineage remained tricky because Europeans often interbred Mexican, Caribbean and Polynesian varieties, sweeping away the molecular trail of crumbs. But French researchers stumbled upon a fix: sweet potato samples preserved in centuries-old herbariums assembled by some of the first European visitors to Polynesia. By analyzing the genetics of these sweet potatoes, ScienceNOW reports, researchers found evidence that Polynesian sailors, rather than Spanish or Portuguese explorers, introduced the now-ubiquitous yam across Southeast Asia and the Pacific.

The researchers compared the herbarium samples to modern sweet potatoes and older specimens and found strong evidence for prehistoric contact between Polynesia and South America. ScienceNOW:

This finding supports the so-called tripartite hypothesis, which argues that the sweet potato was introduced to the region three times: first through premodern contact between Polynesia and South America, then by Spanish traders sailing west from Mexico, and Portuguese traders coming east from the Caribbean. The Spanish and Portuguese varieties ended up in the western Pacific, while the older South American variety dominated in the east, which would explain the genetic differences the French team saw.

As widely used as it is now, the sweet potato could play an even bigger role in feeding people across the world: climate change may help the roots grow even bigger.

More from Smithsonian.com:

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