New research digs into the question of when humans first colonized Australia.
Aboriginal Australian culture is regarded as humanity’s oldest continuous living culture. Existing scientific literature estimated their arrival on the continent of Australia at 65,000 years ago.
However, recent genetics research that analyzes traces of Neanderthal DNA in Homo sapiens suggests the actual origination date was no more than 50,000 years ago.
In collaboration with a colleague from Australia’s La Trobe University, James O’Connell, professor emeritus in University of Utah’s anthropology department, reviewed new findings for a study appearing in the journal Archaeology in Oceania.
The team highlights conclusions from recent and previous studies that argue Homo sapiens and Neanderthals interbred only once, over a period of several thousand years—between 43,500 and 51,500 before present, or BP.
All modern humans, including Indigenous Australians, carry 1–4% Neanderthal DNA. The logic follows that modern Aboriginal Australian ancestors’ arrival on the continent could not have predated this time range.
Moreover, the dating of most archaeological sites across Australia points to a range between 43,000 and 54,000 years.
“The colonization date falls within that interval,” O’Connell says. “That puts it in the same time range as the beginning of the displacement of Neanderthal populations in western Eurasia by anatomically modern humans.”
Other hominids, such as Homo erectus, had lived in Southeast Asia for more than a million years, but had not crossed overseas in large enough numbers to create a stable population in Australia. That is an important measure of the significance of Homo sapiens‘ arrival.
One important Australian outlier among archaeological sites, O’Connell notes, is Madjedbebe, a site dated within a range of 59,000 to 70,000 years ago. The dating technique used in a 2017 study of Madjedbebe published in Nature was optically stimulated luminescence, or OSL.
The technique reads minerals, typically quartz or feldspar, recovered at the site like a “clock” by measuring the energy they have accumulated from surrounding, mildly radioactive sediments when buried. The amount of energy released when they are exposed to light or heat is an index of how long they have been buried.
The site has been subject to sand deposition, which may explain the estimated age of the artifacts. “The question for us has not been about the validity of the date. It’s about the relationship between the date and material evidence of human presence—that is, artifacts. In that part of Australia, many older archaeological sites are in situations where the depositional environment is a sand sheet. Material can move down through those deposits over time.”
Artifacts that are heavier than sand could settle through the sand deposit over time, and as a result, the dating process may have accurately analyzed the age of the sand deposits but not the artifacts they come to contain.
O’Connell also reviewed the hurdles the first people to reach Australia would have faced. That continent is separated from Southeast Asia by a formidable ecological barrier, the 1500 kilometer-wide Wallacean archipelago. Island hopping through it required at least eight separate, open ocean crossings, the longest of which measured 90 kilometers, roughly 60 miles.
Moreover, these journeys would need to support a sizable population. Citing mitochondrial data, O’Connell notes: “Genomic analysis shows that early human colonizing populations included at least four separate mitochondrial lineages. Simple modeling exercises show that establishing each lineage on Sahul required the presence of at least five–10 women of reproductive age, which implies census populations of at least 25–50 individuals per lineage among the founders.”
The analysis indicates that these founding populations arrived within a short timeframe, lasting just a few centuries.
“This strongly suggests that colonizing passage was deliberate, not accidental,” O’Connell says,” and that it required sturdy rafts or canoes capable of holding, say, 10 or more people each plus the food and water needed to sustain those folks on open ocean voyages of up to several days, and of making headway against occasionally contrary ocean currents.”
Altogether, this technological progression adds more weight to a post-50,000-year arrival date, with other innovations and behavioral shifts—including cave art, tools, and ornaments—emerging in that timeframe.
The arrival date for humans in Australia has been a focus of anthropological debate for decades. Although a 70-59,000-year date has received much favorable attention since it was published in 2017, the combination of a large body of archaeological data and an increasing amount of genetic information point to a date less than 50,000 years, the one O’Connell; his coauthor Jim Allen, a retired professor from La Trobe University; and many Australian archaeologists have long favored.
“I would expect in the next five years or so, the pendulum is going to swing back to general agreement for an under 50,000-year date for Australian colonization. It links up with the broader Eurasian record of an out-of-Africa population wave that spreads across Eurasia—a process that occurs over several thousand years. That raises all kinds of questions about why it happens, what it involves, what prompts it, and what changes in behavior are indicated in greater detail than they are now.”
Source: University of Utah
