By Io Gilman
New research involving genetic analysis of DNA samples shows that Native American and Polynesian populations made contact and interbred around 1200 CE. The study, led by Stanford Medical School postdoctoral research fellow Alexander Ioannidis, was published recently in Nature.
Despite being separated by over 2,000 miles of open ocean, the populations reached each other. “It’s some incredible voyaging,” Ioannidis said.
Ancient Native American ancestry was found on the Polynesian Islands of Palliser, Marquesas, Mangareva and Rapa Nui. According to Ioannidis, though people suspected contact between the Rapa Nui people and the Americas, finding native American ancestry on the other islands was unexpected.
“Nobody had really been looking much at these other islands,” Ioannidis said. “The idea was maybe [contact occurred with] Easter Island because it’s the closest [to the Americas].”
According to Ioannidis, the ancient Native American DNA they found in Polynesian people likely all comes from a single ancestor, suggesting that the contact between the populations was brief.
“It looks like a single contact event on some island or by some group and then it spread out to the other islands that have this ancestry,” Ioannidis said.
To get the data for the study, 807 DNA samples were taken from many different populations. According to Ioannidis, collecting the samples required a large team of people familiar with the populations.
“If you want to understand what the issues are locally, you need people who’ve worked with them for a while,” he said.
Senior author Andrés Moreno-Estrada — who used to be a postdoctoral researcher and research associate in the Stanford Department of Genetics, and now leads the Genomics Core Facility, LANGEBIO (Mexico) — also emphasized that the researchers are “committed to community engagement with the population.” According to Moreno-Estrada, the Rapa Nui were interested in learning about their genetic profiles, but previous experiences with researchers made them hesitate to participate in the study.
“They said, ‘Are you going to be just yet another expedition that takes samples and we never hear back of what happened?’” Moreno-Estrada said.
Moreno-Estrada’s group did return a year later, though, with the personal results of each participant, which Moreno-Estrada says surprised the Rapa Nui.
“I think it was a good precedent to really keep the population informed and make them participants in the whole process,” Moreno-Estrada said. The team planned to return to Rapa Nui again this summer, but their trip was canceled due to the coronavirus pandemic; instead, they held a Zoom meeting with community members the day the paper was published to deliver the results and answer questions.
According to Moreno-Estrada, working with populations like Polynesian people, who are underrepresented in DNA databases, is also important for medical reasons.
“The predisposition or the risk to diseases can be very different from one place to the other — and if we don’t know the map of that genetic profile, we will be applying medicine blindly to populations that we don’t know how they’re going to respond to treatments or the risk of different diseases,” Moreno-Estrada said.
Once they had the samples, though, figuring out whether there was ancient Native American DNA in the Rapa Nui’s genomes was difficult.
“The question was whether we could disentangle the facts that the Native American ancestry is only the result of the recent annexation of the island [by Chile], or if the signal that we could observe of Native American ancestry could also be the result of more ancient contacts between the Pacific or Polynesian populations and Native Americans,” said Moreno-Estrada.
The research team likewise encountered difficulties in trying to determine where the Native DNA came from.
“The amount of Native American ancestry on some of these Eastern Polynesian islands is very small,” Ioannidis said. “So it’s enough to say that it’s there, but … to be able to characterize what kind of Native American it is out of all the different groups along the Pacific is not easy.”
They developed a new method where they could “combine together all the different Native American pieces of DNA from the same island, and then, with this still very small amount of DNA, identify where it came from,” Ioannidis said. They ultimately determined that the Zenu in Colombia are the most closely related Native American population to the Polynesian people.
They also dated the contact, using a method that relies on the length of the ancient Native DNA segments in the Polynesian genome. During reproduction, chromosomes exchange genetic material, creating chromosomes with mixes of the parents’ DNA. Thus sections of ancestral DNA get shorter each generation by a predictable amount — allowing researchers to determine that contact occurred approximately 800 to 850 years ago. That date is around two centuries earlier than previous estimates in other genetics studies.
People have long theorized contact between Polynesians and Native Americans. Those who support contact theories have long pointed out that the sweet potato, which was first domesticated in South or Central America, was already in Polynesia by the time Europeans arrived. In addition, the word that the Rapa Nui used for the sweet potato, kumara, is very similar to cumar and cumal, words used for sweet potato in some South American regions.
“I think a contact is the easiest way to explain [how the sweet potato got to Polynesia], and now that we find the contact coming from a region where that word was used, it really suggests that that’s what happened,” Ioannidis said.
As of now, it is unclear if Polynesian DNA is present in Native American communities. According to Ioannidis, because the Native American populations were large, “over the centuries with continued interaction between [Native] populations, that small amount of [Polynesian] ancestry would rapidly be spread in the population and become … very hard to detect — I would say impossible.”
“The only way that we would really be able to see [Polynesian DNA] is with ancient DNA, and you would have to find the bones of a person from this exact specific community near to the time of contact, which would be a really fortunate thing to find,” he added.
Ioannidis appreciates that genetics can reveal untold stories, adding that it is “just fascinating to be able to tell these stories and add genetics to the mix. There’s a lot we know from archaeology, but I think that this is a new tool we can use.”
Ioannidis said he is interested in using these methods to reveal other stories, “especially unwritten things things we couldn’t otherwise tell the story of.”
“So groups that were enslaved or had their culture and history taken away from them — they still carry that history in their own DNA,” Ioannidis said. “Those stories aren’t lost, and we can use techniques like this to trace them back.”
Contact Io Gilman at ioyehgilman ‘at’ gmail.com.