How ancient peoples populated the Pacific islands
"We model ocean migrants as 'infecting' uninhabited islands," he said in a statement.
If the results of the analysis are correct, the colonizers didn't just hop to the nearest islands or drift around hopefully. The study, published in this month's issue of the journal , suggests that those early Pacific seafarers "had a strategy for the best way to discover new places: movement across the ocean in a less risky fashion - often meaning into the wind - and moving to places that were more easily visible."
Distance no object
The study found no evidence to support previous theories of the way speakers of Austronesian expanded their range so dramatically.
For instance, distance wasn't a factor. New Zealand, which is relatively nearby, was settled long after more distant parts of the Pacific, suggesting that people were already adept at long-distance ocean travel when settlement of the Pacific began.
This map of the Pacific shows the estimated number of years ago (years B.P. or before present) various island groups were settled, starting with the Bismarck and Solomon Islands 3,470 years ago. The compass shows the direction of prevailing easterly-southeasterly winds and the directions for safer or more dangerous journeys by early seafarers in canoes who settled the Pacific 3,500 to 900 years ago. A University of Utah study used mathematical modeling to show traveling against the wind during exploratory voyages was likely one of their strategies. If an exploration failed, the seafarers could then turn around and return home safely with the wind. Larger Version
"The colonization of small islands in the vast expanse of the Pacific is one of the most remarkable chapters of human history," the study says. Studying how the Pacific was colonized is important because "migration is a key driver of human cultural and genetic evolution," the researchers add.
The "infection" model
The study looked at the expansion of Lapita people, who emerged from Southeast Asia, inhabited the Bismarck and Solomon islands east of New Guinea about 3,500 years ago and then pushed south and east to become the first people to settle the remote Pacific. They were the ancestors of many Melanesians and Micronesians and all Polynesians.
Bell and colleagues developed a computer simulation they adapted from an epidemiological model of how diseases spread. Instead of using individual characteristics to assess the probability of infection, the model's variables were such factors as island size, distances from other islands, prevalent wind directions and the inferred level of social hierarchy among people living on the island.
Bell described a key math equation of the model as being "like a clock that is ticking through time, and with each ticktock we calculate a probability of an island either being colonized or not. We use the dates we know for roughly when islands were colonized. So as the model moves forward in time, it will suggest some islands to be colonized first rather than others. How well it matches up with the data will distinguish which model comes out on top."
The results held up even when Bell artificially increased uncertainties in the times when specific islands were colonized.
The findings
The analysis showed there was no outward "wave of advance" from a central point, like ripples spreading from a rock dropped in a pond. Distance between islands wasn't a factor in whether an island would be settled or not.
What did fit the colonization data better than anything else was modifying the "wave of advance" concept of distance by the "angle of target". This is a single number representing an island's visibility based on its height, width and distance.
High volcanic islands have a larger angle of target and are more likely to be spotted than low coral atolls. Yet a single large island might have a lower angle of target and be less likely to be discovered than a long archipelago of small islands.
The second-most likely colonization strategy was "risk-minimizing" by heading into the prevailing wind on outward, exploratory journeys, allowing for safer return (with the wind) from failed searches.
The calculations ruled out the idea that people settled high-quality islands first, the habitat-quality model.
"The fact that habitat quality was not a major reason for going somewhere suggests the actual act of moving across the ocean was the major factor in settling the Pacific," says Bell. "Crossing and exploring was the driving force rather than skipping an island and looking for a better island."
"A sea of islands"
Bell, whose mother is Tongan and whose father is a European-born New Zealander, believes the early seafarers saw the vast Pacific as small and draws a parallel with life in the Pacific islands today.
"The idea that distance didn't matter for founding early Pacific societies - there is some continuity with today's island societies, where distance is not a big factor in maintaining interactions among close family groups," says Bell. He notes that many Pacific Islanders today don't bat an eyelash at traveling thousands of miles for weddings and other family occasions "so family relations are maintained across the ocean."
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