Open ArchiveDOI:https://doi.org/10.1016/S0960-9822(00)00734-X
Abstract
Background: Two competing hypotheses for the origins of Polynesians are the ‘express-train’ model, which supposes a recent and rapid expansion of Polynesian ancestors from Asia/Taiwan via coastal and island Melanesia, and the ‘entangled-bank’ model, which supposes a long history of cultural and genetic interactions among Southeast Asians, Melanesians and Polynesians. Most genetic data, especially analyses of mitochondrial DNA (mtDNA) variation, support the express-train model, as does linguistic and archaeological evidence. Here, we used Y-chromosome polymorphisms to investigate the origins of Polynesians.Results: We analysed eight single nucleotide polymorphisms (SNPs) and seven short tandem repeat (STR) loci on the Y chromosome in 28 Cook Islanders from Polynesia and 583 males from 17 Melanesian, Asian and Australian populations. We found that all Polynesians belong to just three Y-chromosome haplotypes, as defined by unique event polymorphisms. The major Y haplotype in Polynesians (82% frequency) was restricted to Melanesia and eastern Indonesia and most probably arose in Melanesia. Coalescence analysis of associated Y-STR haplotypes showed evidence of a population expansion in Polynesians, beginning about 2,200 years ago. The other two Polynesian Y haplotypes were widespread in Asia but were also found in Melanesia.Conclusions: All Polynesian Y chromosomes can be traced back to Melanesia, although some of these Y-chromosome types originated in Asia. Together with other genetic and cultural evidence, we propose a new model of Polynesian origins that we call the ‘slow-boat’ model: Polynesian ancestors did originate from Asia/Taiwan but did not move rapidly through Melanesia; rather, they interacted with and mixed extensively with Melanesians, leaving behind their genes and incorporating many Melanesian genes before colonising the Pacific.
1. Background
The origin of the Polynesians—the people living in the area of the Pacific bounded by Fiji to the west, Hawaii to the north, Easter Island to the east and New Zealand to the south—has long drawn the attention of researchers from different fields. Linguists group all the languages spoken in Polynesia, Micronesia, the main part of island Melanesia (excluding the Papuan languages spoken in New Guinea and a few adjacent islands of Melanesia), island Southeast Asia, mainland Malaysia and Madagascar into one Austronesian language family that originated on or near Taiwan [1, 2, 3]. Recently, a re-analysis of 1,200 Austronesian languages revealed that nine out of the ten subgroups containing 26 languages are spoken exclusively by Taiwanese aborigines, whereas the other 1,174 Austronesian languages belonging to the tenth subgroup are also spoken outside of Taiwan [2, 3]. Archaeological evidence—mostly from pottery remains of the Lapita culture—points to southern China and Taiwan for the origin of Polynesians. Lapita remains, which are widespread throughout Polynesia and island Melanesia dating back to 3,600 to 2,500 years ago, have not been found in New Guinea and Australia, and have been interpreted to be derived from a similar culture established about 6,000years ago in Taiwan and southern China [4, 5, 6, 7].The archaeological and linguistic evidence have given rise to the ‘express-train to Polynesia’ hypothesis for the colonisation of the Pacific [4, 8, 9], according to which Austronesian-speaking people migrated rapidly during the last few thousand years from Asia/Taiwan into the Pacific. Recent genetic data from mitochondrial DNA (mtDNA) have been interpreted to support this hypothesis and a Taiwanese origin of Polynesians [10, 11, 12]. Data from human leukocyte antigen (HLA) genes also suggest Polynesian affinities with Asians [13, 14, 15].An alternative ‘entangled-bank’ hypothesis for the colonisation of Polynesia assumes a long and more complex history of interaction between Polynesia, Melanesia and Southeast Asia and holds that there was no single discrete migration event or ‘express-train’ to Polynesia [[16]]. In this respect, Lapita has also been interpreted as having evolved gradually in island Melanesia and introduced to Polynesia from Melanesia rather than imported from Asia [17, 18]. Whereas most of the mtDNA and HLA data have been interpreted as indicating an Asian/Taiwan origin of Polynesians, the haemoglobin genes of Polynesians do indicate affinities with Melanesians [19, 20, 21, 22]. A third hypothesis, that Polynesians came from South America [[23]], receives no support from any genetic data [12, 24] and is not generally accepted by either archaeologists or linguists [[6]].To date, conclusions from genetic data regarding Polynesian population history are restricted to maternally inherited mtDNA and recombining autosomal DNA. Insights from the male-inherited Y chromosome are not available or are of limited information because of the lack of polymorphic markers in this geographic region [[25]] or the limited numbers of Melanesian and Southeast Asian populations analysed [[26]]. To investigate the origin of Polynesian Y chromosomes, we have therefore undertaken an extensive study of eight Y-chromosomal single nucleotide polymorphisms (Y-SNPs) and seven Y-chromosomal short tandem repeat (Y-STR) loci or microsatellites in 18 populations from Polynesia, Melanesia, Asia and Australia.
2. Results
We initially investigated 28 males from the Cook Islands for eight Y-SNPs (M4, M5, M9, M16, M21, M119, M122 and RPS4Y711). This analysis revealed that every Cook Islander belongs to one of only three Y-chromosome haplotypes (Table 1, Fig. 1), defined by polymorphisms at M9, M122 and RPS4Y711. To investigate the origin of these Polynesian Y-chromosome haplotypes, we analysed an additional 583 individuals from 17 populations from Asia, Australia and Melanesia at the three Y-SNPs that were found to be polymorphic in the Cook Islanders. We also analysed seven Y-STRs (DYS19, DYS389I, DYS389II, DYS390, DYS391, DYS392 and DYS393).Table 1Y-chromosomal haplotypes observed in Polynesia and their frequency distribution in other populations from Melanesia, Asia and Australia.
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