13:00 30 September 2014 by Michael Slezak
Too far east? (Image: Thomas J. Abercrombie/National Geographic Creative)
Expert navigation and advanced boat-building technology were not enough for humans to finally colonise the world’s most remote islands – shifting wind patterns also played a part.
There were no humans on Easter Island in the south-eastern Pacific until the middle ages, when expert Polynesian sailors spread from the central Pacific islands. Within a few hundred years, they colonised previously uninhabited islands all across the South Pacific. But how they did so has remained a matter of some controversy.
Today winds blow from east to west in the tropics, and in the opposite direction further south. This would have made it an epic struggle against the wind to sail eastwards to Easter Island or westwards to New Zealand, and scientists have clashed over whether Polynesian seafaring could have coped with such a task.
The Polynesians would probably have needed fixed-mast canoes to sail against the wind, which there is no evidence of, says Ian Goodwin from Macquarie University in Sydney, Australia. Instead, his research suggests that these pioneering sailors might have had the winds in their favour after all.
“All previous research that’s been done trying to understand this very rapid colonisation of the Pacific tried to grapple with the migration in terms of modern climate,” says Goodwin, who teamed up with anthropologist Atholl Andersonfrom the Australian National University in Canberra.
They wanted to see whether wind patterns could help explain the migrations. Using evidence from tree rings, lake sediments and ice cores, they tried to reconstruct ancient climates. Their work showed that, for a couple of centuries, a unique set of wind changes would have made these journeys easier.
Catching the breeze
The wind record reveals that every few decades there were dramatic shifts in wind direction, corresponding to expansions and contractions of the predominantly warm, moist climates of the tropical regions, caused by warming of the western Pacific Ocean. Many of these events explain the movements of Polynesians’ across the pacific.
From 1080 to 1100, the tropics contracted, moving the westerly winds further north. This would have created ideal sailing routes from the already colonised South Austral Islands to Easter Island – exactly when many archaeologists now think the island was colonised. Later, from 1140 to 1160, the opposite happened. The tropics expanded, and the easterly winds moved further south, allowing migration to New Zealand, which corresponds with archaeological and oral history records.
But the wind changes seem to have stopped as suddenly as they emerged – which could be why there don’t appear to have been any major voyages after 1300
Debating blows on
Terry Hunt, an anthropologist at the University of Oregon in the US, believes the timings are significant. He and his colleagues previously establishedexactly when some of the colonisations happened using radiocarbon dating. “When we wrote our paper, we were saying to ourselves ‘something must have erased distance in the rapid colonization of the remote Pacific.’ These windows may be the critical clue,” he says.
Dilys Johns from the University of Auckland, New Zealand, is more reserved about the role the wind played for the Polynesians’ rapid spread across the South Pacific. “It’s good to know they had chunks of time when it wouldn’t have been as difficult,” she says, but she still believes Polynesians were probably capable of sailing against the winds.
Hunt disagrees. “I think this is a compelling argument that an upwind capability was not necessary for long-distance voyaging, and indeed did not play a role.”
Journal Reference: PNAS, DOI: 10.1073/pnas.1408918111