An analysis of the sweet potato genome indicates that the crop might have grown in the region long before the Americans colonized Polynesia.
A study published Thursday in the journal Current Biology reported that it is possible that sweet potatoes were dispersed to Polynesia from the Americas without the aid of humans. The research suggests that the tubers arrived in the South Pacific islands at least 100,000 years before people did.
Author Robert Scotland from the University of Oxford said that the study's main purpose is to identify the closest wild relative of sweet potato to improve its resistance to pests and diseases and to increase crop yield. The researchers then thought that they could also determine the origin and evolution of sweet potatoes in Polynesia.
"Apart from identifying its progenitor, we also discovered that sweet potato originated well before humans, at least 800,000 years ago," Scotland said. "Therefore, it is likely that the edible root already existed when humans first found this plant."
The researchers conducted a combination of genome skimming and target DNA capture of 199 samples of sweet potato and its closest relative Ipomoea trifida.
One notable specimen is the 250-year-old dried leaf sample collected by Daniel Solander and Joseph Banks in 1769. The two botanists joined Captain Cook's expedition to Polynesia.
Results of the phylogenetic DNA analysis revealed that the samples from sweet potatoes and its other relatives showed unmatched family trees. The analysis also revealed that a lineage split between the modern species and the sample from Americas happened about 100,000 years ago.
Pablo Muñoz-Rodríguez, co-author and a botanist at the University of Oxford, explained that the anomaly could have been a result of hybridization between sweet potatoes and its ancestor. After its progenitors became extinct, further hybridization occurred.
Debate Is Far From Over
Scotland said the study did not only resolve the history and origin of sweet potatoes, but it also provided an alternative method to produce crops. He explained that genetic diversity allows scientists to improve or alter a plant's properties to make them compatible with other species.
Lisa Matisoo-Smith, a molecular anthropologist from the University of Otago in New Zealand, refuted the validity of the study. She said that the researchers did not follow standard protocol for handling DNA samples. She also recommended that the tests be replicated independently.
Researchers find the results intriguing, although they echo Matisoo-Smith's concern on the handling of the specimen, particularly that of the 250-year-old dried leaves sample. Given the need for further verification, this study does not necessarily put an end to the debate on what came first, people or sweet potatoes.
"This paper shows sweet potatoes were already in Polynesia when the islands were first colonized by humans thousands of years ago," said Lars Fehren-Schmitz, a paleogeneticist at the University of California, Santa Cruz. "But it can't prove there was no contact between Polynesians and South Americans before Europeans arrived."