The human settlement of the Pacific Islands

The human settlement of the Pacific Islands represents one of the most recent major migration events of mankind. Polynesians originated in Asia according to linguistic evidence or in Melanesia according to archaeological evidence.

To shed light on the genetic origins of Polynesians, we investigated over 400 Polynesians from 8 island groups, in comparison with over 900 individuals from potential parental populations of Melanesia, Southeast and East Asia, and Australia, by means of Y chromosome (NRY) and mitochondrial DNA (mtDNA) markers.

Overall, we classified 94.1% of Polynesian Y chromosomes and 99.8% of Polynesian mtDNAs as of either Melanesian (NRY-DNA: 65.8%, mtDNA: 6%) or Asian (NRY-DNA: 28.3%, mtDNA: 93.8%) origin, suggesting a dual genetic origin of Polynesians in agreement with the “Slow Boat” hypothesis.

 Our data suggest a pronounced admixture bias in Polynesians toward more Melanesian men than women, perhaps as a result of matrilocal residence in the ancestral Polynesian society. Although dating methods are consistent with somewhat similar entries of NRY/mtDNA haplogroups into Polynesia, haplotype sharing suggests an earlier appearance of Melanesian haplogroups than those from Asia.

Surprisingly, we identified gradients in the frequency distribution of some NRY/mtDNA haplogroups across Polynesia and a gradual west-to-east decrease of overall NRY/mtDNA diversity, not only providing evidence for a west-to-east direction of Polynesian settlements but also suggesting that Pacific voyaging was regular rather than haphazard. We also demonstrate that Fiji played a pivotal role in the history of Polynesia: humans probably first migrated to Fiji, and subsequent settlement of Polynesia probably came from Fiji.

The colonization of Polynesia which ranges from Hawaii in the north to Easter Islands in the east, Fiji in the west, and New Zealand in the south, is still a matter of debate. According to linguistic evidence, Polynesian languages are closely related to each other and belong to the Austronesian language family that can be traced back to East Asia, in particular to the present-day languages of Taiwanese Aborigines (Blust 1999; Diamond 2000).

 Furthermore, linguistic evidence (Gray and Jordan 2000) is usually interpreted to support the “Express-train” hypothesis (Diamond 1988), according to which Polynesian ancestors moved rapidly from Eastern Asia into the Pacific without significant admixture with Melanesians (we use the term “Melanesia” in the geographic sense, to include here the mainland of New Guinea and surrounding islands, also referred to as Near Oceania).

Archaeological evidence suggests that western Polynesian islands (Fiji, Futuna, Samoa, Tonga) were settled 2,100–3,200 years ago by people belonging to the so-called Lapita cultural complex that originated 3,000–3,500 years ago in Island Melanesia, in particular the Bismarck Archipelago (Kirch 2000).

However, some archaeologists argue that the Lapita cultural complex originated about 6,000 years ago in China and thus associate the spread of Austronesian languages with the Neolithic spread of material culture, including agriculture and Lapita, from East Asia into the Pacific under the Express-train scenario (Bellwood 1978; Diamond and Bellwood 2003), whereas others suggest a strict Melanesian origin of the Lapita cultural complex (White et al. 1988; Terrell 1989; Terrell et al. 2001).

 Besides the 2 “extreme” models, the “Express train” assuming an Asian origin of Polynesians with no or little admixture of ingenious Melanesians and the “Entangled bank” assuming a long and complex history of human interactions starting from the first occupation of Melanesia in the Pleistocene (Terrell 1988), there are additional “intermediate” models such as the “Triple I” (Green 1991).

The Triple I model assumes that components of the Lapita cultural complex are results of Intrusions of nonindigenous Asian components together with the Integration of indigenous Melanesian elements and new Innovations (Green 1991).

In contrast to the clear evidence for an Asian origin of Polynesian languages and a probable Melanesian origin of the Lapita material culture found in Polynesia, the genetic origin of Polynesians is still contentious. Studies of maternally inherited mtDNA markers have favored an Asian origin of Polynesian maternal lineages (Melton et al. 1995; Redd et al. 1995; Sykes et al. 1995; Trejaut et al. 2005) in support of the Express-train hypothesis.

 In contrast, studies of paternally inherited DNA markers from the nonrecombining portion of the Y chromosome (NRY) have revealed a mostly Melanesian origin of Polynesian paternal lineages (Kayser, Brauer et al. 2000; Capelli et al. 2001; Underhill, Passarino, Lin, Marzuki et al. 2001; Hurles et al. 2002) supporting the “Slow Boat” hypothesis (Kayser, Brauer et al. 2000).

The Slow Boat model assumes that Polynesian ancestors originated in Eastern Asia but mixed extensively with indigenous Melanesians before colonizing the Pacific (Kayser, Brauer et al. 2000).

Unfortunately, a similar term “Slow boat to Melanesia” was subsequently used to suggest a Southeast Asian genetic origin of Polynesians in the Pleistocene based on mitochondrial DNA (mtDNA) evidence (Diamond 2001; Oppenheimer and Richards 2001). Studies of autosomal DNA markers suggest different scenarios depending on the markers used, for example, a Melanesian origin of Polynesian hemoglobin genes (Hill et al. 1985, 1987) versus an Asian origin of Polynesian human leucocyte antigen (HLA) genes (Mack et al. 2000; Mack and Erlich 2005).

In this study, we have used NRY and mtDNA markers to investigate the paternal and maternal genetic origin of over 400 individuals from 8 different Polynesian island groups by comparing them with over 900 individuals from Melanesia, Southeast and East Asia, and Australia. This significant increase over previous studies, both in populations and markers analyzed, provides new insights into the history of the human colonization of the Pacific.

https://academic.oup.com/mbe/article/23/11/2234/1333210