NEW YORK – Native South Americans and Polynesians may have had contact around 1200 AD, according to a new genomic analysis.
Based on shared cultural elements and the presence of sweet potatoes, a crop native to the Americas, in Polynesia, scientists have long suspected that there may have been early contact between Polynesian and Native South American populations. In particular, scientists have guessed there may have been contact between individuals living on the Polynesian island of Rapa Nui, also known as Easter Island, and the Americas, as it is the closest inhabited Polynesian island, but previous studies have revealed conflicting results.
By analyzing genomic variation between more than 800 individuals with Polynesian or Native American ancestry, an international team of researchers has homed in on evidence of admixture between the groups, including contact that occurred prior to European colonization. They traced the pre-European contact admixture back hundreds of years and suggested there was a single contact event between the Indigenous people of today's Colombia and eastern Polynesians, as the researchers reported Wednesday in Nature.
"Through this research, we wanted to reconstruct the ancestral roots that have shaped the diversity of these populations and answer deep, long-standing questions about the potential contact between Native Americans and Pacific Islanders, connecting two of the most understudied regions of the world," senior author Andrés Moreno-Estrada, the head of genomic services at the National Laboratory of Genomics for Biodiversity in Mexico, said in a statement.
He and his colleagues collected saliva samples from 807 individuals, from 17 Polynesian islands and 15 Native American groups from the Pacific coast. Through a global ancestry analysis of the samples using the Admixture algorithm, they uncovered genomic regions that were Polynesian, Native American, European, and African in origin.
A number of Polynesian populations had genomic segments that were of European origin, consistent with the European groups that colonized the various islands, but they also harbored two Native American ancestry components. One component appears in conjunction with a Spanish European ancestry signature and likely represents the immigration of admixed Chilean individuals to Rapa Nui, following Chile's annexation of the island in 1888.
The other Native American ancestry component, however, is older. An ancestry-specific PCA approach placed this Native American ancestry component of Pacific Islanders among the Zenu people of Colombia. This finding, the researchers noted, is consistent with linguistic and other evidence, including similarities between the Polynesian and coastal South American names for sweet potato: kumala and cumal.
The researchers timed this admixture event between Native Americans and Polynesians to about 1200 AD, which is about when the islands were being settled by Polynesians. The admixture timing estimate varied slightly from island to island, with Rapa Nui exhibiting a later introgression date of 1380, possibly due to the influence of the later Chilean-origin admixture there.
Based on their modeling and identity-by-descent analysis, the researchers suggested one contact event took place between eastern Polynesians and Native Americans. They noted, though, that where this contact took place is not yet clear — either in Polynesia or South America — but it likely was not on Rapa Nui as the contact timing predates its settlement. The mixed population likely spread from central eastern Polynesia to other parts of Polynesia, including Rapa Nui.
"These spectacular results have major implications for future discussions concerning early migrations and interactions in Polynesia," Uppsala University's Paul Wallin wrote in a related commentary, also appearing in Nature.
He further suggested that the researchers' model next be analyzed in conjunction with material-culture studies, ethno-historical records, linguistic analyses, and studies of plant and animal spread.