Did the early Australians really tread the continent 65,000 years ago, or does their genetic history tell a different story? The intersection of ancient DNA and archaeology is reshaping this long-standing debate, drawing fresh interest in both chronologies and methods.
The presence of Neanderthal DNA within Indigenous Australians is one such pillar on which the genetic argument revolves. Recent genomics, including high-coverage sequencing of ancient Eurasians, placed the prevailing Neanderthal-Homo sapiens interbreeding event to a period between 50,500 to 43,500 years ago. In Nature, they write, this Neanderthal ancestry originates from the same admixture event that can be detected in all other non-Africans and date this event to 45–49 ka, close to or more recent than most previous estimates. The news is clear: every non-African group living today, including Australian Aborigines, carry Neanderthal DNA from this single event. If so, then their ancestors would not have migrated to Sahul before this genetic encounter.
But archaeological findings at Madjedbebe, a northern Australian rock shelter, still contradict this version. Archaeologists have uncovered more than 10,000 artifacts, such as the world’s oldest ground-edge axe head, seed-grinding stones, ochre “crayons,” and hearths. Advanced dating methods, in this case optically stimulated luminescence (OSL), have placed the earliest occupation layer at Madjedbebe at around 65,000 years ago. The excavation team, led by Chris Clarkson, used millimeter-accuracy laser total stations to map artifact positions and conducted experiments to assess sediment displacement, and concluded that post-depositional disturbance was slight.
The stratigraphic integrity of Madjedbebe is nevertheless still contentious. The sandy matrix is cited by critics as a path along which artifacts can travel downwards, artificially enhancing their age. Not even Peter Hiscock, an early occupation date advocate, reports without warning caution that “to say that humans first set foot in Australia exactly 65,000 years ago may be ‘a somewhat optimistic interpretation of the data'”. However, the coincidence of OSL and radiocarbon ages with independent laboratory verification has made it more certain that the site is of this age.
The genetic dimension of the argument hinges on molecular clock techniques, which derive the timing of evolutionary events from the accumulation of genetic change. These clocks also have their own margins of error. Rates of mutation and recombination vary among populations and through time, introducing error margins into divergence estimates. As Peter Veth pointed out, “can we rely on current assumptions underlying these molecular clocks to test Australian archaeological evidence?” This is especially troubling as the generation interval and recombination hotspots may shift, with subtle impacts upon inferred chronologies.
Beyond the issue of when, the archaeological record at Madjedbebe and in Southeast Asia gives us a glimpse into the cognitive and cultural capacity of early human individuals. The discovery of figurative cave paintings in Sulawesi, Indonesia, which were at least 51,200 years old tells us that narrative storytelling and symbolic behavior had been present there long prior to the alleged “Paleolithic Revolution” around 50,000 years ago. As Adam Brumm stated, “storytelling is a hugely important part of human evolution, and possibly even it helps to explain our success as a species”. The proposal is that advanced symbolic expression evolved independently and gradually by different regions, and not as an instant development linked with contact with Neanderthals.
Sahul itself had extraordinary technological advancedness involved in colonizing and crossing over from Southeast Asia implied nautical crossings in great distances of open sea and represented “the largest maritime migration yet undertaken” by early humans. Early boats are rare in the archaeological record, but the presence of exotic raw materials at Madjedbebe sourced more than 25 kilometers away points to great mobility and social networks. As more molecular and archaeological data come to light, the history of the first Australians is still an active and contentious frontier. Each new discovery a scrap of ancient DNA or pigment-stained grinding stone shines new light upon our understanding of how and when Homo sapiens initially settled the remotest edge of the ancient world.
