By analyzing genetic markers specific to sweet potatoes in both modern samples of the plant and older herbarium specimens, the researchers discovered significant differences between varieties found in the western Pacific versus the eastern Pacific. 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.Apart from the famous Heyerdahl voyage (which has recently become the subject of a 2012 movie), there was some other research regarding the introduction of Polynesian chickens to Chile. I have not followed the genetics of that part of the world very closely, but it's my impression that such a link between Polynesia and South America has not been found in the human populations of the two regions.
January 21, 2013
Sweet potato genome provides link between South America and Polynesia
The actual PNAS paper seems to be still under embargo, but here's a news story in Science about the new research: