Mitochondrial Genetic Diversity and its Determinants in Island Melanesia

For a long time, many physical anthropologists and human geneticists considered Island Melanesian populations to be genetically impoverished, dominated by the effects of random genetic drift because of their small sizes, internally very homogeneous, and therefore of little relevance in reconstructing past human migrations. This view is changing. Here we present the developing detailed picture of mitochondrial DNA (mtDNA) variation in eastern New Guinea and Island Melanesia that reflects linguistic distinctions within the region as well as considerable island-by-island isolation. It also appears that the patterns of variation reflect marital migration distinctions between bush and beach populations. We have identified a number of regionally specific mtDNA variants. We also question the widely accepted hypothesis that the mtDNA variant referred to as the ‘Polynesian Motif’ (or alternatively the ‘Austronesian Motif’) developed outside this region somewhere to the west. It may well have first appeared among certain non-Austronesian speaking groups in eastern New Guinea or the Bismarcks. Overall, the developing mtDNA pattern appears to be more easily reconciled with that of other genetic and biometric variables

A Cautionary Tale on Ancient Migration Detection: Mitochondrial DNA Variation in Santa Cruz Islands, Solomon Islands

Over the past decade, the origin of the first Malayo-Polynesian settlers of the island Pacific has become a contentious issue in molecular anthropology as well as in archaeology and historical linguistics. Whether the descendants of the ancestral Malayo-Polynesian speakers moved rapidly through Indonesia and Island Melanesia in a few hundred years, or whether they were the product of considerable intermingling within the more westerly part of the latter region, it is widely accepted that they were the first humans to colonize the distant Pacific islands beyond the central Solomon Islands approximately 3000 years ago. The Santa Cruz Islands in the Eastern Solomons would have most likely been the first in Remote Oceania to be colonized by them. Archaeologically, the first Oceanic Austronesian settlement of this region appears to have been overlain by various later influences from groups farther west in a complex manner. Molecular anthropologists have tended to equate the spread of various Austronesian-speaking groups with a particular mitochondrial variant (a 9-base-pair [bp] deletion with specific D-loop variants). We have shown before that this is an oversimplified picture, and assumed that the Santa Cruz situation, with its series of intrusions, would be informative as to the power of mitochondrial DNA haplotype interpretations. In the Santa Cruz Islands, the 9-bp deletion is associated with a small number of very closely related hypervariable D-loop haplotypes resulting in a star-shaped Bandelt median network, suggesting a recent population expansion. This network is similar to Polynesian median networks. In a pairwise mismatch comparison, the Santa Cruz haplotypes have a bimodal distribution, with the first cluster being composed almost entirely of the 9-bp-deleted haplotypes—again attesting to their recent origins. Conversely, the nondeleted haplogroups bear signatures of more ancient origins within the general region. Therefore, while the profiles of the two sets of haplotypes indicate very distinctive origins in different populations with divergent expansion histories, the sequence of their introduction into the Santa Cruz Islands clearly does not follow simply