Ancient Solomon Islands mtDNA: assessing Holocene settlement and the impact of European contact

Abstract

Archaeologists, linguists and geneticists generally agree that Near Oceania was subject to two major pulses of human dispersal: a Pleistocene occupation around 40,000 BP and a Late-Holocene migration at 3500 BP commonly associated with the Austronesian expansion out of Taiwan. The latter led to the development of the Lapita cultural complex in the Bismarck Archipelago which resulted in the settlement of Remote Oceania and there are a variety of competing models (express train, slow boat, entangled bank, etc.) used to explain this. Recent genetic studies have focused on this issue, but none of them have taken into consideration the bias possibly introduced by 19th-century historically reported population decline caused by European contact. In this paper we present a case study to test the effect of 19th–20th century colonial impact on the mitochondrial DNA diversity of Solomon Islanders and to investigate the complex stratigraphy of settlement in this archipelago during and after the Lapita period. We extracted DNA from hairs and teeth belonging to 21 individuals collected by the Somerville expedition during the late 19th-century, and typed them for mitochondrial DNA (mtDNA) hypervariable region I (HVS-I) and the intergenic COII/tRNALys 9-base pair deletion (9 bp-del). Comparison of these genetic data with those available from the modern Solomon Islanders and Southeast Asian and Oceanic populations conflicts with the hypothesis of drastic changes in Solomon maternal genepool diversity, indicating that the last century putative bottleneck is not detectable through our genetic data. In addition, the ancient and modern Solomon haplogroup distribution (e.g. M27 haplogroup) suggests, in agreement with some archaeological and linguistic models, that Early Lapita populations expanding out of the Bismarck Archipelago had little or no contact with indigenous non-Austronesian populations in Bougainville and the Solomon Islands. This finding indicates smaller scale analyses reveal a more complex reality of genetic admixture in some parts of Oceania than is often assumed in current debates.