Extreme patterns of variance in small populations: placing limits on human Y-chromosome diversity through time in the Vanuatu Archipelago

The human genetic history of Oceania: near and remote views of dispersal

The human history of Oceania is unique in the way that it encompasses both the first out-of-Africa expansion of modern humans to New Guinea and Australia as well as the last regional human occupation of Polynesia. Other anthropological peculiarities of Oceania include features like the extraordinarily rich linguistic diversity especially of New Guinea with about 1,000 often very distinct languages, the independent and early development of agriculture in the highlands of New Guinea about 10,000 years ago, or the long-term isolation of the entire region from the outside world, which lasted as long as until the 1930s for most of the interior of New Guinea. This review will provide an overview on the genetic aspects of human population history of Oceania and how some of the anthropological peculiarities are reflected in human genetic data. Due to current data availability it will mostly focus on insights from sex-specifically inherited mitochondrial DNA and Y-chromosomal DNA, whereas more genome-wide autosomal DNA data are soon expected to add additional details or may correct views obtained from these two, albeit highly complex, genetic loci.

Autosomal and X-linked single nucleotide polymorphisms reveal a steep Asian-Melanesian ancestry cline in eastern Indonesia and a sex bias in admixture rates

The geographical region between mainland Asia and New Guinea is characterized by numerous small islands with isolated human populations. Phenotypically, groups in the west are similar to their neighbours in mainland Southeast Asia, eastern groups near New Guinea are similar to Melanesians, and intervening populations are intermediate in appearance. A long-standing question is whether this pattern primarily reflects mixing between groups with distinct origins or whether natural selection has shaped this range of variation by acting differentially on populations across the region. To address this question, we genotyped a set of 37 single nucleotide polymorphisms that are evolutionarily independent, putatively neutral and highly informative for Asian-Melanesian ancestry in 1430 individuals from 60 populations spanning mainland Asia to Melanesia. Admixture analysis reveals a sharp transition from Asian to Melanesian genetic variants over a narrow geographical region in eastern Indonesia. Interestingly, this admixture cline roughly corresponds to the human phenotypic boundary noted by Alfred Russell Wallace in 1869. We conclude that this phenotypic gradient probably reflects mixing of two long-separated ancestral source populations-one descended from the initial Melanesian-like inhabitants of the region, and the other related to Asian groups that immigrated during the Paleolithic and/or with the spread of agriculture. A higher frequency of Asian X-linked markers relative to autosomal markers throughout the transition zone suggests that the admixture process was sex-biased, either favouring a westward expansion of patrilocal Melanesian groups or an eastward expansion of matrilocal Asian immigrants. The matrilocal marriage practices that dominated early Austronesian societies may be one factor contributing to this observed sex bias in admixture rates.