HMN 2025: How Humans first entered Australia 60,000 years ago via two routes

Debate has long surrounded when humans first traveled into Sahul, the ancient landmass that is now Australia, New Guinea and Tasmania. Now, a study published in Science Advances, lends credence to the theory that the first humans entered Sahul around 60,000 years ago from parts of Southeast Asia.

A tale of two chronologies

Among the scientific community, there are two prominent theories as to when humans first migrated into Sahul—both supported by various studies. The “short chronology” theory posits that humans entered Sahul between 47 to 51 thousand years ago.

Many genetic studies have favored the short chronology, citing mitochondrial DNA (mtDNA) and Y-chromosome data. In addition, some say that the process by which DNA from archaic human populations was passed down to the ancestors of modern humans through interbreeding occurred too recently to be consistent with longer timelines.

Meanwhile, the ‘long chronology’ theory states that modern humans arrived in Sahul at least 60,000 years ago. This theory, supported by the new study, is also supported by some genome-wide studies. However, some researchers have pointed out problems with these studies. Still, some archaeological evidence of human settlements within Sahul has been dated back to times in line with the long chronology.

“There are more data from Australia, with the oldest known sites located in the Northern Territory. Roberts and colleagues combined OSL (optically stimulated luminescence) and radiocarbon to estimate an occupation age of 53 to 60 ka at Nauwalabila I. More recently, Clarkson and team estimated an age of 53 to 65 ka at Madjedbebe.

“The lowest occupation horizon is bracketed by multiple OSL dates, replicated across four excavated sections, but there are signs of vertical displacement of artifacts, and an age range of 53 to 60 ka, similar to Nauwalabila I, is likely,” the study authors explain.

Insights from the molecular clock

Archaeological evidence from Sahul is scarce, so researchers have primarily relied on genetic methods to determine periods of likely migration in the region. The methods used in this study involved analysis of 2,456 mitochondrial genomes. The team says the dataset encompasses the full range of diversity of the Indigenous populations of Australia, New Guinea, and Oceania, and includes a lineage related to those of New Guinea in an archaeological sample from Wallacea.

The study uses “molecular clock” techniques, which analyze the number of mutations that occur within a given time. This allows scientists to estimate the time of divergence between genetic groups by measuring the rate of genetic mutations.

While there are differing methods that result in different rates, the preferred method in this study resulted in time ranges that coincide with the long chronology. However, the team says that the other method (Fu) does coincide more with the short chronology, but that “assumptions and methodology deliberately minimize the ages, and that other assumptions and methodologies, even with the Fu rate, raise the estimates into the long chronology range.”

The team also integrated genome-wide and Y-chromosome data and checked climatological data, which also supported the long chronology timeline.

Two distinct routes into Sahul

The team’s analysis showed two distinct genetic groups, both originating from Southeast Asia (and from Africa further back). However, it is clear that these groups split off around the time that they entered Sahul, taking two separate routes: a northern route into New Guinea and a southern route into Australia from the ancient landmass of Sundaland.

The study authors write, “The mitogenome evidence reported here further shifts the balance of the debate toward the likelihood of at least two distinct dispersal routes into Sahul, both northern and southern, with a common ancestry in Sundaland, supporting separate analyses of primarily Australian and New Guinean lineages.

“Although it may be impossible to pinpoint the precise landfall points with genetic data, modeling of exposed MIS4 island chains suggests that the likely arrival points were the Bird’s Head peninsula of West New Guinea and the northwest Sahul shelf.”

Maybe even more surprising is that these groups had to cross up to 100 km of water to get to their new settlements—providing evidence of early seafaring.

While the debate may not be entirely settled, this research provides some compelling evidence of early migration timing and settlement regions of the people that became Indigenous Australians and Papuans—helping to shed more light on their origins and heritage.

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