Academic journal article Archaeology in Oceania

A Model-Based Age Estimate for Polynesian Colonization of Hawai'i

Academic journal article Archaeology in Oceania

A Model-Based Age Estimate for Polynesian Colonization of Hawai'i

Article excerpt

Abstract

A model-based Bayesian calibration using [sup.14]C data from paleoenvironmental cores and materials introduced to the islands by Polynesian colonists estimates that the islands were likely colonized sometime late in the first millennium AD. Two calibrations, one using [sup.14]C dates on floral materials and the other using [sup.14]C dates on floral and faunal materials, indicate that archaeological materials yield relatively imprecise estimates of the colonization event with 95% highest posterior density regions 3-5 centuries long. Materials introduced to the islands by Polynesians date to two periods, one that coincides with the colonization event, and another some 3-6 centuries later. A disparity between colonization and the first reliably dated archaeological evidence of human activity is identified and estimated to be 1-4 centuries long.

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In the sixty years since an unexpectedly old age estimate was returned by the first [sup.14]C date from Hawai'i (Libby 1951), archaeologists have used [sup.14]C dating evidence to estimate when Polynesians first colonized the islands. Initially, the [sup.14]C method was seen as a precise scientific replacement for the settlement dates derived from traditional histories, which relied on genealogical information and estimates of the average length of a generation to calculate when Polynesians colonized the islands. Somewhat surprisingly, the use of [sup.14]C dating evidence has failed to yield a precise estimate. In fact, over time, it has produced a wider range of settlement estimates than genealogical dating with all its vagaries. Published estimates based on [sup.14]C data now range from the beginning of the common era (Hunt and Holsen 1991) to the thirteenth century AD (Wilmshurst et al. 2011a). Much of this variability is due to Hawaiian archaeologists' uncritical use of the [sup.14]C method, in particular the on-going failure to control for the effects of old wood (Dye 2000; Dye and Pantaleo 2010). Another important source of variability is the ad hoc methods used to interpret [sup.14]C dates when estimating the colonization event. A model-based Bayesian approach is proposed here as a solution to this persistent problem.

Brief review of ad hoc age estimates for Polynesian colonization

Archaeologists have developed three different approaches to estimating when Polynesians colonized Hawai'i. These include a search for early sites, evaluations of lists of [sup.14]C dates compiled from site excavation reports, and evaluations of [sup.14]C dates from paleoenvironmental investigations. All of these approaches have been implemented in an ad hoc way, without benefit of an explicit chronological model.

Early [sup.14]C-based estimates of Polynesian colonization of Hawai'i were framed in the context of arguments for the ages of purportedly early sites. Arguments for an early establishment of three coastal sites were made, including Pu'u Ali'i, Site HI (Emory and Sinoto 1969); Bellows, Site O18 (Pearson et al. 1971); and the Halawa Valley Dune, Site MO-A1-3 (Kirch and Kelly 1975), which was interpreted as somewhat later than the other two. At each of the three sites artifactual or structural evidence was found that differed from expectations based on the known ethnographic and museum records and which was interpreted as indicating some antiquity for the site: at Pu'u Ali'i this was a multifaceted sequence of change in various types of fishing gear (Emory et al. 1968); at Bellows an artefact assemblage with an unusual shell coconut grater, pearl shell fishhooks, and adzes with trapezoidal and triangular cross sections (Pearson et al. 1971); and at Halawa Valley, a buried round-ended house, untanged and ground adzes, and various early fishhook types (Kirch and Kelly 1975).

The early age estimate for each of these sites was subsequently challenged. Dye (1992) showed that the argument for an early date at HI was based on outliers among the dated samples and used an analysis of cumulative probability curves to argue for a much later fifteenth century date for establishment of the site. …

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