Genes reveal how and when humans reached remote corners of Pacific – The Economist

Sep 25th 2021

THE COLONISATION of the Pacific Ocean was one of the great feats of human navigation. Groups of a few dozen people, travelling in canoes carved from trees, discovered and settled hundreds of tiny islands separated by vast spans of open water. They found their way using the stars, dead reckoning and study of the wind.

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Exactly when these trips occurred, and in which order, is unclear. Oral histories are richly detailed, but vague on dates. The colonisers moved too fast for linguistic analysis to yield answers. Archaeological evidence is scant. But a new paper by Alex Ioannidis of Stanford University and 26 other scholars claims to have clarified this fuzzy history using genetics, by analysing the DNA of 430 modern-day Polynesians.

Polynesian prehistory reaches back to the island now called Taiwan. From there, starting in around 2500BC, the ancestors of todays Pacific Islanders are thought to have spread through the Philippines and Indonesia to western Polynesian islands such as Samoa and Fiji. They paused there for centuries or more, before venturing on to the vast emptiness of the Pacific. The authors focus on this second expansion.

The team relied on a genetic pattern called the founder effect. Each canoe probably carried only a few dozen people, out of hundreds or thousands living on the originating island. These pioneers descendants should thus be less genetically diverse than people on the island from which their ancestors came. Every subsequent colonisation should have created a new genetic bottleneck. The authors determined the order of the voyages by finding this signature in modern genomes, while excluding confounding chunks of DNA contributed by later arrivals from Europe.

The dates are less certain than the sequence. Genomics counts time in generations, not years. However, research on other places in pre-modern time periods, such as 17th-century Iceland and rural Quebec in the 1800s, suggests an average generation length of 30 years.

The study shows that the Polynesians moved quickly once they set out into open ocean. One of the first colonisation voyages probably set off in around 830AD from Samoa to Rarotongathe largest of the Cook Islands, a 67-square-kilometre speck about 1,500km to the south-east. By 1050, explorers seem to have reached Tahiti. Just 50 years later, they had probably set foot in the Tuamotu Islands, a 1,500km-long series of tiny atolls. A heroic 2,600km journey from Mangareva to Easter Island, one of the remotest dots of land on the planet, is likely to have occurred in around 1210.

This chronology is of course inexact. However, the authors are confident in the sequence, and say that the total dating error should be only around 60 years. Moreover, their account is compatible with both archaeological records and Polynesians own oral histories. For those who know how to read it, the history of the Polynesian voyagers lives on in their descendants.

Source: Paths and timings of the peopling of Polynesia inferred from genomic networks, by A.G. Ioannidis et al., Nature, 2021

This article appeared in the Graphic detail section of the print edition under the headline "To the ends of the Earth"

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Genes reveal how and when humans reached remote corners of Pacific - The Economist