New mitochondrial data reported in the Proceedings of the National Academy of Sciences on May 7, 2007, supports the somewhat still controversial Australian colonization as having occurred at about 50,000 bp--and that it was a single founder population who were subsequently isolated from the rest of the world.
Evidence for the Australian Settlement
The first Australians arrived on the continent, according to Australian archaeological consensus, probably at least about 45,000 years ago. Archaeologists still debate the precise date; but there are over 150 archaeological sites that date to at least 40,000 years ago, and fairly firm older evidence has been identified at sites such as Devil's Lair (Western Australia, 50,000 bp), Lake Mungo (New South Wales, 62,000 bp), Malakunanja II (Northern Territory, 56,000-61,000), and Nauwalabila I (Northern Territory, 30,000-60,000 bp).
Approximately 45,000 years ago, the sea level was some 200 meters lower than it is today, and Australia and adjacent islands (including New Guinea and Tasmania) were connected in what archaeologists refer to as Sahul. Sahul was still separated from mainland southeast Asia (called Sunda) by a deep channel in which many small islands are located still, called Wallacea. Wallacea was a natural barrier to the movement of animals for many many thousands of years, which led to the isolation and hence creation of so many different species of animal in Australia found nowhere else on the planet.
The archaeological site evidence for the fairly late 45,000 year-old human colonization of Australia is bolstered by the fact that more than 20 genera of large-bodied fauna (or megafauna) disappeared from Sahul during the middle-late Pleistocene. Some Australian researchers have blamed this occurrence on fires set by incoming populations. Like other recognized megafaunal extinctions world wide, however, the real reason for the extinctions is still in question.
Out of Africa or Multiregional Hypothesis?
The archaeological evidence from Australia has been used in the past to support two broad-based theories of human evolution: the Out of Africa hypothesis and Multiregional hypothesis. Basically, the OOAH postulates that Homo sapiens evolved once, in Africa, and migrated outward, replacing the earlier forms of human being; while the MRH suggests that human evolution occurred several times in several parts of the world as a result of an African-derived Homo sapiens group mixing genes with (er, breeding with) older human forms such as Homo erectus or Neanderthals.
Recent investigations into mitochondrial DNA (mtDNA) of Aboriginal Australians and New Guineans, published on May 7, 2007 in the Proceedings of the National Academy of Sciences, however, supports the OOA hypothesis. An international research team discovered that mtDNA data of Australians and New Guineans fall within the same mitochondrial branches as other human populations who left Africa between 50,000 and 70,000 years ago. These data suggest to researchers that the settlement of the entire region of Australia and New Guinea was undertaken by one early founder group shortly after the African exodus, and that they were subsequently isolated from the remainder of the world as the water level rose. The isolation of the Australians from the rest of us likely resulted in the divergent morphologies and the limited stone tool industries noted in archaeological assemblages.
Paleontologists are very much divided concerning this issue, with several important and respected researchers on both sides of the argument. A third hypothesis about the peopling of Australia growing in importance is called the Southern Dispersal Route holds a great deal of promise, suggesting that early modern humans may have left South Africa and followed the coastlines to Asia.
Australian Aboriginal History and Human Evolution
This is undoubtedly not the end of the discussion about the population of Australia and New Guinea, but it is one more piece of evidence pointing towards understanding the evolution of the modern human being.
Hudjashova, Georgi et al. 2007. Revealing the prehistoric settlement of Australia by Y chromosome and mtDNA analysis. Proceedings of the National Academy of Sciences Early Edition 10.107.0702928104
O'Connell, James F. and Jim Allen 2004 Dating the colonization of Sahul (Pleistocene Australia--New Guinea): A review of recent research. Journal of Archaeological Science 31:835-853.
Note: More references on this interesting issue may be found on page two of this report.