The prehistoric colonization of the remote Pacific was arguably the most ambitious migration in human history. Though there is archeological data available for the colonization of many of the major islands, there is still debate about where various settlers originated and the routes they may have used to reach habitable land.

A recent study published in PNAS harnesses the power of high resolution climatic and oceanographic datasets to argue that seasonal and semiannual weather changes were influential in structuring ancient Pacific voyaging. Based on this model, Samoa was the likely staging area for the colonization of east Polynesia, and the success of various colonization ventures to New Zealand and Easter Island depended heavily on the season.

The authors used a Seascape computerized model that randomly selected frequency-weighted monthly current and wind data collected by the US Navy’s Marine Climatic Atlas of the World. It combined these probabilistic weather patterns with the speeds for small seafaring vessels, although the precise type of ship used for various migrations is not known. The sailing patterns the model produced were combined with land distribution data to determine the most likely short-hop trajectories between islands. Trajectories started in the eastern Philippines and Solomon Islands.

The authors found that easterly winds dominated much of the oceanic area near the Philippines and most of Micronesia. But the waters near the Maluku Islands and other regions of Micronesia likely had westerly winds during the Southern Hemisphere summer months, which would have impeded migrations eastward. They found that crossings to the Islands of Palau that originated in the southern Philippines would take approximately one month before migrants would reach their destination.

The authors also considered how El Niño influenced migration. Their simulations showed that El Niño produced dry conditions over the Philippines that may have motivated travelers to keep moving east. Travel from the Philippines to the Maluku Islands most likely included Micronesian Island landfalls but could also have included crossings to the Mariana Islands.

Travel to central and eastern Micronesia would likely have included trips through the Solomon Islands, Vanuatu, and Fiji. These trips would have been heavily dependent on the seasons, with more successful voyages from the western Solomon Islands occurring between July and October and the most successful crossings through Fiji occurring in the month of August. These limits were in part due to seasonal weather patterns and in part due to seasonal dryness caused by El Niño.

Shortest-hop departures could reach the Islands of Samoa by starting in Palau, moving through Micronesia, and reaching Samoa through west Polynesia. Of all the plausible trajectories that were modeled in these experiments, however, this is the only one that has no supporting archeological evidence. Perhaps this is because there were some unknown weather patterns in the relevant centuries that impeded travelers from taking this route, or perhaps the relevant evidence has been lost due to erosion or other phenomena.

The authors found that the islands of Hawai’i were most easily reached during Northern Hemisphere autumns via direct oceanic voyages originating in the Marquesas and the Society Islands. The simulations also showed that trips from the Society Islands to New Zealand were most likely to occur between November and March.

Overall, the wind and distance limits provided by these simulations showed that seasonal and climatic variability heavily influenced the migration patterns through remote Oceania. Changes in precipitation might have motivated ancient migration patterns, while knowledge of how winds changed with seasons would have increased the likelihood of successful voyages to new islands.

These new models provide the chance to examine how Pacific Islanders may have planned oceanic voyages centuries ago. They also provide a hint about the motivation: seasonal and interannual climatic fluctuations likely drove the migration, and they helped the voyagers develop new traveling and navigational techniques.

PNAS, 2016. DOI: 10.1073/pnas.1612426113 (About DOIs).