08 July 2020 22:34
"The sweet potato is native to the Americas, yet it's also found on islands thousands of miles away," Ioannidis said. "On top of that, the word for sweet potato in Polynesian languages appears to be related to the word used in Indigenous American languages in the Andes." The overlap in culture made some archaeologists and historians think it was not only feasible, but likely, that the potato's arrival in Polynesia was the result of the two peoples mingling. The researchers believe that the Polynesians landed in what is now Colombia. It is also possible, though less likely due to their coastal travel norms, that one or two ships carrying Native Americans could have sailed off course and run into Polynesia, Ioannidis said. Without scientific evidence, the idea of overlap was just conjecture.
Earlier, other groups of researchers turned to the genetics of the sweet potato, hoping to show that the domesticated potatoes from South America and Polynesia were genetically one and the same. But their efforts to trace the tubers have been inconclusive, as the sweet potato's genetic origins were too complex to definitively point to human-mediated spread. Other studies have analyzed ancient DNA from bones belonging to Native Americans and native Polynesians. Ancient DNA samples, however, are often degraded, so these studies were unable to provide sufficient evidence that the two populations shared a moment in history. Carriers of history Ioannidis' team took a different, big data approach, analyzing the DNA of hundreds oIndigenous people from Polynesia, Mexico and South America. Before collecting any samples or conducting genetic analyses, the researchers visited the communities to explain the study, gauge interest in participation and ask for consent. The scientists then collected saliva samples from 807 participants on 17 Polynesian islands and 15 Native American groups along the Pacific coast of the Americas from Mexico to Chile, conducting genetic analyses to look for snippets of DNA that are characteristic of each population and for segments that are "identical by descent," meaning they are inherited from the same ancestor many generations ago. "We found identical-by-descent segments of Native American ancestry across several Polynesian islands," Ioannidis said. "It was conclusive evidence that there was a single shared contact event." In other words, Polynesians and Native Americans met at one point in history, and during that time people from the two cultures produced children with both Native American and Polynesian DNA. Statistical analyses confirmed the event occurred in the Middle Ages, around A.D. 1200, which is "around the time that these islands were originally being settled by native Polynesians," Ioannidis said. Using computational methods developed as part of Ioannidis' graduate work, the team then localized the source of the Native American DNA to modern-day Colombia. "If you think about how history is told for this time period, it's almost always a story of European conquest, and you never really hear about everybody else," Ioannidis said. "I think this work helps piece together those untold stories — and the fact that it can be brought to light through genetics is very exciting to me." Other Stanford authors of the study are graduate student Alexandra Sockell; former graduate student Julian Homburger, PhD; former postdoctoral scholar Genevieve Wojcik, PhD; and professor of biomedical data science and of genetics Carlos Bustamante, PhD. In addition to Moreno-Estrada, other researchers from the National Laboratory of Genomics for Biodiversity in Mexico, as well as researchers from the University of Oslo; the Pontifical Catholic University of Chile; the National Institute of Genomic Medicine, Mexico; University of Oxford; National Autonomous University of Mexico; University of Colorado, Denver; University of California, San Francisco; and the University of Chile, Santiago, contributed to the work. The research was supported by the George Rosenkranz Prize for Health Care Research in Developing Countries; Mexico's National Council for Science and Technology; the International Center for Genetic Engineering and Biotechnology in Chile; the American Society of Engineering Education; the National Library of Medicine; Chile's Scientific and Technological Development Support Fund, National Fund for Scientific and Technological Development and National Commission for Scientific and Technological Research; the National Institute for Health Research Oxford Biomedical Research Center; and the Wellcome Trust.