Ancient DNA from Papua New Guinea reveals centuries of genetic isolation

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The first ancient human genomes analyzed from Papua New Guinea reveal that some of the early groups that lived there were completely genetically isolated from their neighbors, showing there was little intermarriage at multiple points in time, a new study finds.
New Guinea is the second largest island in the world, after Greenland. It and its outlying isles were vital launch points for early seafaring journeys into the wider Pacific, culminating with the settlement of some of the last islands on Earth to be permanently inhabited, scientists noted. However, until now, much remained unknown about its ancient genetic history.
In a new study, researchers analyzed ancient DNA from the bones and teeth of 42 people who lived as long as 2,600 years ago on Papua New Guinea — the nation inhabiting the eastern half of New Guinea — and the nearby Bismarck Archipelago, northeast of the main island.
"This was a very long time in the making," study co-lead author Kathrin Nägele, an archaeogeneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, told Live Science. "DNA preservation in tropical environments is extremely challenging."
Previous research suggested that New Guinea and outlying areas were first settled more than 50,000 years ago. Much later, by about 3,300 years ago, new seafaring peoples with Asian ancestry arrived at the Bismarck Archipelago. This group, which archaeologists have dubbed the Lapita culture, is renowned for their intricate pottery and farming practices, which included raising pigs, dogs and chickens, as well as growing coconuts, bananas, yams and varieties of breadfruit.
The new findings unexpectedly revealed the earliest known inhabitants of the Bismarck Archipelago and the Lapita people did not mix genetically for centuries. However, one individual examined suggested they were the result of intermixing about 2,100 years ago.
"Despite the co-occupation, it seems the different groups didn't mix for a long time, which is quite unusual for human encounters," study co-lead author Rebecca Kinaston, an anthropologist and director of BioArch South, an archaeology and forensic anthropology consultancy in New Zealand, said in a statement.
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These findings also shed light on the ancestry of remote Oceanic islands such as Samoa, Tonga and Vanuatu. They support prior research that Papuans and the Lapita independently arrived at those distant isles and intermarried there, as opposed to mixing first at New Guinea and nearby isles and then voyaging to those remote lands.
"It suggests the Papuans were separately capable of remarkable seafaring," Nägele said. "The seafaring hunter-gatherers on Papua New Guinea have likely been underestimated, just as hunter-gatherer societies tend to be underestimated all over."
Another striking discovery occurred when the scientists analyzed two communities that inhabited the south coast of Papua New Guinea between 150 and 500 years ago. "Although these two communities only lived a few kilometers apart, they were unexpectedly genetically different," Nägele said. "Looking into the direct family relations between the two sites, we had to go six generations back to find a common ancestor, which means that for six generations, the two groups did not mix despite the close proximity and no geological barriers between them."
Both groups had a mix of Papuan-related and Southeast Asia-related ancestries. One group, buried at the site Eriama, showed more of the Papuan-related ancestry compared to the site of Nebira, where Asian ancestry was the larger component.
Why did these groups stop mixing with each other? One possibility is a climatically challenging time on New Guinea between 1,200 and 500 years ago, which may have seen increased El Niño events, such as major droughts.
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"Settlements were abandoned — people might have retreated to unknown places that were more viable," Nägele said. "We think wherever these people were, they started engaging in new trade networks. Nebira appeared to engage more with coastal groups, and Eriama more with inland groups from the highlands. This might have led to different identities, different cuisines, and other differences that led to cultural diversification."
In the future, the researchers hope to collect older genetic data, as well as samples from the highlands of New Guinea and the first Asian-related people to arrive on the coast of the island. "Papua New Guinea is such a diverse place in so many regards, that we have only just scratched the surface of what is to learn about the past of the second largest island in the world," Nägele said.
The scientists detailed their findings June 4 in the journal Nature Ecology & Evolution.