Australia: The Land Where Time Began

A biography of the Australian continent 

Whole Genome of Sample of Australian Aboriginals with Deep Aboriginal Ancestry Studied for Genetic Diversity

Sahul (comprised of mainland Australia, New Guinea and Tasmania) was probably settled not long after anatomically modern humans (AMH) migrated from Africa, though the details of this migration are not well understood. Debate has centred on whether the settlement that took place in the Pleistocene was first settled by a single wave which was followed by divergence on a regional basis into Aboriginal Australian and New Guinean populations (common origin) or whether different parts of the continent were initially populated independently. Relatively few DNA studies have been carried out in Australia, though if disease-association mapping methods are to be evaluated successfully and applied across population an understanding of regional variation in genomic structure and diversity will be important. In this paper McEvoy et al. report a genome-wide investigation of Australian Aboriginal SNP diversity in a sample of participants from the riverine region. A deep common origin with populations from New Guinea and Melanesia, with little evidence that substantial later migrations occurred until the arrival of Europeans very recently, is demonstrated by the phylogenetic relationship of these Australian Aboriginal people to a range of other populations around the world. This study provides valuable and robust insights into an early, important phase of the colonisation of the continents of the Earth by anatomically modern humans. McEvoy et al. suggest a broader survey of Australia, that includes diverse geographic sample populations, is required to appreciate fully the unique population history and consequent genetic heritage, as well as the importance both to the understanding of health issues.

According to McEvoy et al. there is strong evidence, both genetic and fossil, that anatomically modern humans evolved in Africa about 200,000 BP, and a subset migrated out of Africa much later, about 80,000-40,000 BP, that populated the remainder of the world (Cavalli-Sforza & Feldman, 2003). It is suggested by mtDNA that these migrants left Africa by the “southern route,” crossing the Red Sea to Arabia, and then moved relatively rapidly along the coast to Southeast Asia and Australia (Macaulay et al., 2005). Some of the earliest evidence of human habitation outside Africa has been found in Australia that has been dated to at least about 46,000 BP and probably to about 60,000 BP (O’Connell & Allen, 2004;  Balme et al., 2009; Oppenheimer, 2009), in spite of its distance from Africa. It is suggested by archaeological evidence that New Guinea immediately to the north of Australia and Melanesia to the northeast, collectively termed Near Oceania, regions that were also settled by about 40,000 BP (Groube et al., 19086). Sea levels were lower during the Pleistocene and when the first humans entered the region and it was the time when the Australian continent of the present was connected to Tasmania in the south and New Guinea in the north, in the single landmass known as Sahul. Details of the dispersal routes and timing of the settlement remain debated. It is proposed by the common origin hypothesis that a single major migration to Sahul from Eurasia occurred following which there was a divergence into separate geographic populations. By contrast, according to the independent origin model a multiwave early settlement of Sahul with migrations that were largely independent to New Guinea of the present-day and mainland Australia. There is debate also around whether the first settlers were followed by later migration waves.

Variation along the entire genome can now be interrogated simultaneously as a result of advances in genotyping technology, and this has revolutionised the study of human genetic diversity, which provides new insights into population history as well as facilitating the discovery of genes by genome-wide association studies (GWASs) (McCarthy et al., 2008).

In spite of its early and unique place in human global colonisation, however, there has been relatively little investigation of genetic diversity among Australian Aboriginal people. This is due in part to the unease felt by some Aboriginal people about genetic research because of the legacy of research experiences in the past (van Holst Pellekaan, 2000). In the past a limited number of studies have generally focused on traditional Y chromosome and mtDNA markers, and there have been no surveys of diversity in the whole genome. GWAS genotyping and analytic approaches are typically geared to populations of European origin with the focus on diseases and conditions that are prevalent among these people, and not on diversity. It will first be necessary to gain a fuller understanding of the population history of Aboriginal Australia, and the present genetic legacy of that past, in order to extend gene discovery studies, as well as their long term health benefits, to Australia Aboriginal people (Rosenberg et al., 2010; Need & Goldstein, 2009).

Sources & Further reading

1. McEvoy, B. P., et al. "Whole-Genome Genetic Diversity in a Sample of Australians with Deep Aboriginal Ancestry." The American Journal of Human Genetics 87(2): 297-305.