Discoveries by CSULB Professor Change Timeframe of Human Colonization in Eastern Polynesia
2010-12-27 · By Editor
New research by an international team of scholars shows early human colonization of Eastern Polynesia took place much faster and more recently than previously proposed.
They describe their discoveries in a Dec. 27 Proceedings of the National Academy of Sciences Early Edition article (www.pnas.org; also at www.eurekalert.org) co-authored by Carl Lipo, associate professor of anthropology at California State University, Long Beach (CSULB); team leader and paleoecologist Janet Wilmshurst of Landcare Research in Lincoln, New Zealand; Terry L. Hunt, professor of anthropology at the University of Hawaii at Manoa; and Atholl Anderson, professor of prehistory, archaeology and natural history at Australia National University’s College of Asia and the Pacific in Canberra.
The study was based on an analysis of the validity of more than 1,400 radiocarbon dates from 47 islands in the region collected from their own and other researchers’ published studies.
Polynesians settled in Samoa around 800 B.C., then moved to colonize the region in two distinct phases—earliest in the central Society Islands between A.D. 1025 and 1120, four centuries later than previously assumed. Then between 70 and 265 years later, dispersal continued in one major ‘pulse’ to all remaining islands including New Zealand, Hawaii and Easter Island (Rapa Nui) between A.D. 1190 and 1290.
The timing and sequence of this remarkable event has been highly debated and poorly resolved, precluding the understanding of cultural and ecological change that followed.
“This is an amazing feat of Polynesian sea voyaging and discovery, and represents a rate of dispersal unprecedented in oceanic prehistory,” Wilmshurst said. “It’s even more incredible given that these isolated islands are spread across a vast area of the Pacific Ocean from the subtropics to the sub-Antarctics. Nearly all of the 500 or so islands were discovered, despite being scattered across an area of ocean the size of North America.” The team noted that the voyagers probably benefited from improved canoes and sailing vessels as well as favorable winds resulting from frequent El Niño weather conditions.
Lipo performed the statistical analyses at Cal State Long Beach. He is co-founder of the Institute for Integrated Research in Materials, Environments, and Society (IIRMES), a state-of-the-art lab that conducts collaborative research across the physical, natural and social sciences.
He has extensively studied Easter Island (Rapa Nui), and realized that the possible timeframe of its earliest colonization was similar to New Zealand, which had been extensively studied by Wilmshurst and Anderson. The four researchers met in Hawaii and decided to collaborate on this new study.
The study sorted all radiocarbon-dated materials into sample classes including categories of short-lived plant remains such as seeds or small twigs, unidentified wood charcoal, bone and marine shells, which Lipo said are the least likely sample material to suffer from contamination or calibration issues, and most likely to date an event. Newer radiocarbon dating equipment and techniques also contribute to greater accuracy.
“An example of a Class 1, or most reliable sample, would be something like a rat-gnawed seed,” Lipo said. “It’s not just the seed, because the seed could fall off the tree and often be preserved well in caves for hundreds of years. But we know that rats came with humans and rats love seeds, so rat gnawing and seeds indicates humans were there.
“This is the beginning of recognition that we can’t just accept dates for just whatever they are; we have to link them between what’s being dated and what is the human event,” he continued. “That’s true, say, for a piece of coral. You can date the coral, but the question is when did the coral die? Did it die before the person picked it up and turned it into something, or did it die at the point at which they picked it up? That matters, because it could be quite a big difference in dates. When you need that resolution, you have to be careful.”
As a result, the team developed a model that better predicts a more accurate time span that can be applied to radiocarbon dating elsewhere in the world.
The new research now provides an updated timeline and sequence for the region’s colonization, and means existing models of human colonization, ecological change and historical linguistics for the region now require substantial revision. The work resolves long-standing paradoxes and offers a robust explanation for the remarkable uniformity of East Polynesian culture, human biology and language, Wilmshurst said.
Anderson said the team chose an objective ‘top-down’ approach to evaluate the entire archaeological radiocarbon database for East Polynesia as a single entity. “This allowed all radiocarbon dates, irrespective of their context within an archaeological deposit, to be categorized according to their reliability to provide an accurate and precise age for initial colonization on each island,” he said.
“Unidentified charcoal, bones and marine shell contain a substantial risk of error associated with them which can make the age of the sample appear older than it really is. These are the very materials commonly used by some researchers to date the age of an archaeological site and to support longer chronologies,” said Hunt.
Anderson added that, “As the probability of just one type of sample material providing only younger radiocarbon dates is low, our new results are robust and objective. It has been nearly 20 years since the last appraisal of the timing and pattern of initial human colonization in east Polynesia. Now we have more than 10 times the number of radiocarbon dates available to us, and from a larger number of islands, so the time was ripe for a new and rigorous, systematic analysis.”
Hunt said the remarkable similarities in artifacts documented in the “archaic East Polynesian” assemblages of the Societies, Marquesas, New Zealand, and other islands reflect the same relative forms, or homology, such as in fishhooks, adzes and ornaments, with late and rapid dispersals over the region. “Similarities of form attributed to continuing inter-island group contacts may actually reflect sharing that occurred in mobility associated with colonization and not a later phase of long-distance interactions.”
Hunt said linguistic similarity, often used to trace relationships of populations in East Polynesia according to a longstanding model of relatively slow, incremental expansion now needs to be reconsidered.
Later colonization now shortens the timeframes of human impacts on island ecosystems, particularly deforestation, and plant and animal extinctions.
Environmental transformations may have occurred over decades rather than centuries and include impacts on both terrestrial and marine biota caused by human hunting; predation by introduced animals such as the Polynesian rat, dog, and pig; as well as the human use of fire within the short occupational chronology they propose.
“Islands have long been used as models for saying, ‘What happens when humans arrive?’” Lipo said. “Well, a lot happens, but now it happens in a much shorter amount of time, so the degree of impact is much greater; the rate of change that needs to be taken into consideration. The composition of species rapidly changes on these islands.”