- Experts from the US and Mexico studied Polynesian and Colombian genomes
- They found that modern Polynesians contain traces of Native American DNA
- Contact between the groups occurred on the South Marquesas in 1,150 AD
- This was around the time that Polynesians arrived in the area from the west
- It finally explains why sweet potatoes come from the Americas and Oceania
Native Americans reached Polynesia 800 years ago by raft and interbred with local islanders — centuries before European explorers arrived in the Pacific.
Researchers from the US and Mexico used large-scale genetic analyses to show that modern-day Polynesian populations contain traces of Native American DNA.
Statistical analysis revealed that prehistoric Polynesian populations first met and interbred with people from what is today Colombia around the year 1,150 AD.
This event — which took place on the South Marquesas islands — occurred at roughly the same time Polynesians first arrived in the area from the west.
The finding finally confirms a long-running theory that the two groups had met — and explains why sweet potatoes from the Americas can be found in Polynesia.
Native Americas may have sailed on a raft like the Kon-Tiki — the 1947 vessel led by the explorer Thor Heyerdahl which crossed from Peru to the Polynesian Islands.
The notion that Native American and Polynesian populations underwent prehistoric interactions has long been a subject of debate for archaeologists and historians.
While some experts questioned how the two groups, separated by thousands of miles of open ocean, could have interacted, others pointed to a seemingly unlikely clue for the meeting — the sweet potato.
The starchy root vegetable was originally cultivated in Central and South America but, prior its dispersal by European colonists, could also be found in one other place — the islands of Oceania.
'The sweet potato is native to the Americas, yet it's also found on islands thousands of miles away,' said paper author Alexander Ioannidis of Stanford University.
'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 connections suggested that either Polynesians once landed in South America (most likely Colombia) and brought the potato home with them — or, alternatively, that some Native Americans and their vegetable once ended up in Polynesia.
Efforts to prove that the tubers were once exported from South America to Oceania by analysing the plant's genome, however, proved fruitless — with experts finding the sweet potato's genetic history too complex to conclusively reveal its origins.
Attempts to compare ancient DNA preserved in the bones of Native Americans and native Polynesians also proved inconclusive, with the genetic material having become too degraded to establish a link between the populations.
Dr Ioannidis and colleagues, however, took a different track — analysing DNA samples from 807 modern-day Polynesians and Colombians sourced from across 17 of the Polynesian islands and 15 Native American groups along the Pacific Coast.
In particular, the team sought out segments of DNA that are characteristic of the different populations, alongside those that are 'identical-by-descent' and could therefore be attributed to the owners having had a shared ancestor in the past.
The team's large-scale modern genetic analysis was able to prove what studies of the sweet potato itself and ancient bones were not.
'We found identical-by-descent segments of Native American ancestry across several Polynesian islands,' Dr Ioannidis said.
This, explained, provided 'conclusive evidence' for a 'shared contact event' prehistoric Polynesian and Native American peoples — one in which children with a parent from each group were born.
Further analysis of the genetic signals revealed that the event occurred around 1,150 AD — during Europe's Middle Ages — and, Dr Ioannidis said, 'around the time that these islands were originally being settled by native Polynesians.'
Alongside this, the team were also able to confirm the previous theory that the Native Americans who interacted with the Polynesians came from the region that, today, is Colombia.
'If you think about how history is told for this time period, it's almost always a story of European conquest — you never really hear about everybody else,' said Dr Ioannidis.
'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,' he added.
'Genomics is at a stage where it can really make useful contributions to answering some of these open questions.'
The full findings of the study were published in the journal Nature.