A genetic study has helped shine a light on how the Polynesian islands of the central and southern Pacific – some of which are thousands of kilometres apart – were populated over the past thousand years.
at Stanford University in California and his colleagues analysed the DNA of 430 people of Polynesian descent to map their genetic ancestry.
Polynesia is made up of around 1000 islands that span one-third of the world. It includes New Zealand, Hawaii, Easter Island (Rapa Nui) and Samoa.
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are believed to have reached Samoa, thought to be the first island in Polynesia to be inhabited, about 3000 years ago. These people – probably using double-hulled canoes – went on to populate several other islands in the Pacific.
“We’ve had a general idea of how the islands of Polynesia were populated,” says Ioannidis. “But this is the first study to give us a far more detailed picture.”
The researchers first had to figure out the order in which the islands were discovered.
They did this by taking advantage of a genetic phenomenon called the founder effect, in which there is reduced genetic variation within a population if there are few initial members. This can happen when a small number of people settle on an island. If a small subset of that population then goes on to settle on another island, a second founder effect occurs, reducing genetic diversity again in a subtle but detectable way – and so on.
By comparing the total genetic diversity in the DNA of the study’s participants across the islands, the team was able to tell which populations came from where first. The first migration across the ocean was from Samoa to the Cook Islands – a voyage of 1550 kilometres – around AD 830, according to the researchers.
The team then determined clearer dates for the migrations by comparing specific DNA sequences in the genomes of the study’s participants. If two Polynesian people on different islands have specific identical parts in their DNA, it means they share an ancestor.
“With each generation removed from that ancestor, this shared part of DNA gets smaller and smaller,” says Ioannidis. So the smaller the shared DNA, the more time has passed since that ancestor was alive, giving us a better idea for when that ancestor migrated.
The researchers discovered that Easter Island was probably one of the last to be populated, around AD 1100. Famous for its mysterious megalithic statues, the island’s population is closely related to the populations on Marquesas and Raivavae islands – which are both over 3500 kilometres from Easter Island – according to the new analysis.
All these islands or island clusters are home to striking statues that are unlike any found in the rest of Polynesia. The genetic analysis suggests the same group of people made all these megalithic structures.
The findings tie into previous research suggesting that Polynesians interacted with Native Americans around this time also.
“We still don’t know what these statues were for, but we know [they] come from this heroic voyaging culture,” says Ioannidis.
“It is very important to understand the history of eastern Polynesia because it is the last region being settled by humans,” says at the University of Tübingen in Germany. “This new study adds to a more nuanced picture on the order and direction of those initial human voyages.”
Nature
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