Australia: The Land Where Time Began

A biography of the Australian continent 

Australian Prehistoric Settlement as Revealed by Y chromosome and mtDNA Analysis

Published, as well as new samples of Australian Aboriginals and Melanesians were analysed for variations of their Y DNA (n=522) and mt DNA (n=172), and the profiles that resulted were compared with the branches known so far with the global mtDNA and Y chromosome tree.

i)                   It was confirmed that all Australian lineages fall within the mitochondrial founder branches M and N and the Y chromosomal founders C and F, which are associated with the migration of anatomically modern humans from Afric ≈50 ka to 70 ka. No evidence of any archaic maternal or paternal lineages in Australia was revealed by the analysis, in spite of some suggestively robust features in the Australian fossil record, therefore weakening the argument for continuity with any earlier Homo erectus populations in Southeast Asia.

ii)                The complete mtDNA sequence tree shows that Australian Aboriginals are most closely related to the autochthonous populations of New Guinea/Melanesia, which indicates prehistoric Australia and New Guinea were initially occupied by one and the same colonisation event in the Palaeolithic ≈50 ka, which agrees with the current archaeological evidence.

iii)              A considerable isolation following the initial arrival is indicated by the deep mtDNA and Y chromosomal branching patterns between Australia and most other populations around the Indian Ocean.

iv)              Hudjashov et al. detected only a minor secondary gene flow into Australia, and suggest this could have occurred before rising sea levels submerged the land connection between Australia and New Guinea ≈8 ka, and therefore calls into question that certain significant developments in later Australian prehistory, the emergence of a backed blade lithic industry, and the linguistic dichotomy, were motivated externally.

Human evolution – population genetics

Human are believe to have occupied the Australian  continent at least 50,000 ka (Stringer, 2002) At a time when there was a land bridge between the Australian mainland and what is now New Guinea and when only narrow straits separated the region from the Eurasian landmass, such as the barrier known as Wallacea, a gap of ocean and islands requiring a number of comparatively narrow ocean crossings that prevented the wildlife of Eurasia and Australia from mixing, even at times of low sea level, with the exception of a few such as bats and birds. The Australian fossil record has remained not well known. The fossil record of Australia contains anatomically human humans (AMH) that are among the oldest known outside Africa that has been dated to ≈46,000 ka (Bowler et al., 2003; O’Connell & Allen, 2004), in spite of the large geographic distance from Africa, the homeland of AMH (Vigilant et al., 1991). Also, in Australia the oldest known skeletal material at Lake Mungo is of a gracile type, whereas at archaeological sites such as Kow Swamp younger skeletal finds are of a robust morphology (Brӓuer, 1989). Among some modern Australian Aboriginal people elements of this robust morphology have been retained, such as in the form of pronounced brow ridges (supraorbital tori) (Larnach & Macintosh, 1970). A number of explanations have been proposed for the inconsistent morphological record, such as that the AMH interbred with Southeast Asian Homo erectus so that some of their genomic material has been added to the gene pool of the modern humans to some degree (Brӓuer, 1989; Thorne & Wolpoff, 1992), or that it is the result of multiple migrations to Australia which gave rise to differing morphologies at different times, such as hypothetical new migrants from India (Huxley, 1870), or that the genetic isolation of Australia has been long enough for marked continent-/Australian-specific features to arise on the Australian continent (Pardoe, 1991; Brown, 1992; Lahr, 1996; Sengupta et al., 2006; Richards et al., 2006).

The intensification of density and complexity of different stone tools in Australia during the Holocene and the emergence of backed blade stone tool technology is indicated by archaeological data (Mulvaney & Kamminga, 1999). Also at about the same time, 3,500-4,000 years ago, the first dingoes (Canis lupus dingo) appear in the fossil record of Australia, and have been suggested to have arrived with new arrivals of humans from India (Gollan, 1985), as well as new stone tool types (Glover & Presland, 1985). This is a debate that is ongoing (Mulvaney & Kamminga, 1999; Corbett, 1985; Savolainen et al., 1985).

A diversity of interpretations have resulted from recent molecular studies, which range from a deep though undated split that distinguishes Australia Aboriginal people even from their immediate neighbours to the north in New Guinea (20), to a very recent migration event that occurred in the Holocene sometime in the past 10,000 years (21,22).

According to Hudjashov et al. an attempt can now be made to clarify some of the salient features of the record of the Australian population history and confirm its considerable isolation, by using new samples from Australia and New Guinea which have been screened for variations in the Y chromosome and the mt DNA, and benefiting from the increasing genetic coverage available in Australia (Vigilant et al., 1985; Brӓuer, 1989; Forster et al., 1998; Redd & Stoneking, 1999; Redd et al., 2002; van Holst Pellekaan et al., 1998; Huoponen et al., 2001; Ingman & Gyllensten, 2003; Ingman et al., 2000; Kivisild et al., 2006; Kayser et al., 2006;  van Holst Pellekaan et al., 2006; Friedlaender et al., 2007; Underhill et al., 2001; Underhill et al., 2000).

Conclusions

A single early founding group occupying both Australia and New Guinea a relatively short period of time following the exodus from Africa ≈50-70 ka, at a time when Australia and New Guinea were joined into a single continent, Sahul, which made it necessary to make crossings only across narrow straits, as in crossing Wallacea, is pointed to by the results of the mitochondrial and Y chromosome analysis that have been presented in this paper. A small founding population and subsequent isolation of Australia and, to a lesser extent, New Guinea, from the remainder of the world, is indicated by the deep, specific lineages of the present within the former landmass of +. Hudjashov et al. suggests that these founder events could possibly underlie the divergent morphological development that is seen in the Australian human fossil record, and might also explain the remarkably restricted range of Australian Pleistocene lithic industries and bone artefacts compared to contemporaneous cultures in other parts of the world (Mellars, 2006).

Sources & Further reading

1. Hudjashov, G., et al. (2007). "Revealing the Prehistoric Settlement of Australia by Y Chromosome and mtDNA Analysis." Proceedings of the National Academy of Sciences of the United States of America 104(21): 8726-8730.