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Ancient DNA sheds light on Maori settlement

Maori arrival Ancient DNA preserved in the teeth of the first known New Zealanders, who died more than 700 years ago, is helping shed new light on the settlement of Polynesia, researchers report.

Scientists think New Zealand was the last major landmass to be permanently settled by humans, drawing to a close a dispersal process that began in Africa around 65,000 years ago.

But questions remain about the origins and genetic diversity of those first settlers, and the routes they took to New Zealand, say anthropologists Dr Lisa Matisoo-Smith and Dr Michael Knapp from the University of Otago.

The researchers addressed those questions by studying the teeth of people who had been buried at the Wairau Bar archaeological site in the north-eastern South Island of New Zealand, which dates to the period of earliest settlement of New Zealand, between 1285 and 1300 AD.

The tribal group Rangitane-ki-Wairau agreed to samples being removed for DNA analyses and other biological studies prior to the repatriation and reburial of all of the remains.

The researchers ground the teeth to a fine powder and dissolved the powder to release mitochondrial DNA. After being purified, the DNA was sequenced using a new technology that can produce tens of thousands of short sequences.

"These short DNA sequences are like puzzle pieces in a jigsaw puzzle with 50,000 pieces. Using powerful computers we can put these short reads back together in the correct order to assemble the sequence of the complete mitochondrial genome of each individual we sequenced," says Knapp.

"What we found was that each individual that we got DNA sequences from Wairau Bar was different - they had unique mutations."

Artefacts at Wairau Bar suggest the colonists came directly from East Polynesia, and the new DNA evidence is consistent with this, says Matisoo-Smith.

"Now that we have identified specific markers in the mitochondrial genome of these individuals we can start to look for these markers in East Polynesian populations and perhaps identify an island or islands where we also find these mutations."

"These are the first complete ancient mitochondrial genomes sequenced in the Pacific. They provide evidence that there is potentially enough genetic variation to allow us to finally identify the specific homelands and map the specific migration routes the ancient Polynesian voyagers took as they settled the Polynesian triangle, ultimately reaching the shores of New Zealand 700 to 750 years ago," says Knapp.

Significant genetic diversity

Palaeoecologist Janet Wilmshurst, from Landcare Research in Lincoln, New Zealand, says the study throws new light on the settlement of the eastern Pacific.

"The discovery that the Wairau Bar people retained significant genetic diversity casts serious doubt upon the idea of Polynesia having been settled via small accidental or unplanned voyages. Such a settlement pattern would have eliminated much genetic diversity," Wilmshurst says.

"Recently, our group showed that the settlement of the eastern Polynesian islands was much more rapid than previously thought. Rapid settlement of so many islands suggests large, organised migratory populations of men and women, and the results of [this study] appear to support this model. The rapidly improving techniques used in ancient DNA labs make this an exciting time for archaeological research."

The methods used in this study could be used to obtain further ancient mitochondrial DNA genomes from across Polynesia, which would help clarify the details surrounding the last major expansion of modern humans, Wilmshurst says.

"It is a tribute to these researchers and the Rangitani iwi that they took the opportunity offered by what has been, in other countries, a contentious process of repatriation and reburial of human remains, to advance science and enrich cultural understanding. How amazing that we not only know where the first Polynesian settlers of New Zealand were buried, but we also have a tantalising glimpse into what they did, who they were, and potentially where they originated from."

Emeritus Professor Atholl Anderson from the Australian National University agrees that the unexpected genetic variation within this small sample of early Polynesian colonists has important implications for thinking about the colonisation process.

"We know that [genetic evidence] in modern Maori suggests that initial colonisation involved several hundred each of males and females, and that is consistent with traditional narratives of multiple canoes landing in New Zealand about 20 generations ago," says Anderson.

"However, if it turns out - as this latest study hints - that the variation was significantly greater again amongst the ancestral Maori population then are we obliged to think of even greater numbers of people from a wider catchment of East Polynesia, and if so what caused such a substantial migration?"