A new study of nearly 2,500 genomes may have finally settled the debate about when modern humans arrived in Australia. Using a diverse database of DNA from ancient and contemporary Aboriginal people throughout Oceania, researchers have determined that people began to settle northern Australia by 60,000 years ago and that they arrived via two distinct routes.
Experts have long debated the date that humans first arrived in Australia, a feat that required the invention of watercraft. While some researchers have used genetic models to support a "short chronology" of 47,000 to 51,000 years ago for the arrival, others have marshaled archaeological evidence and Aboriginal knowledge in support of the "long chronology," in which the first arrivals happened 60,000 to 65,000 years ago.
"This is the most comprehensive genetic study to date addressing this question, and it lends strong support to the long chronology rather than the short chronology," study co-author Martin Richards, an archaeogeneticist at the University of Huddersfield in the U.K., told Live Science in an email.
The team's analysis also revealed two distinct sets of people arriving via northern and southern routes. "This conclusion fits very well with the archaeological and oceanographic/paleoclimate evidence for an entry into Sahul at around 60,000 years ago," Richards said.
To reach their conclusions, the researchers used a molecular clock approach, which assumes that mutations in DNA sequences occur at a fairly constant rate over time. By looking at the differences in two DNA sequences, researchers can estimate when those sequences diverged from one another.
In the study, the research team used several statistical methods to analyze mitochondrial DNA (which is passed down through the mother's line) and Y-chromosome data (which is passed down through the father's line). All of their statistical models lined up with a date of about 60,000 years ago for the settlement of northern Australia.
But the genetic data also revealed two distinct settlements around the same time. One group of people arrived in Australia via southern Sunda (the Indonesian islands), while another came from northern Sunda (the Philippine archipelago).
The two groups were initially part of the same population that moved out of Africa around 70,000 to 80,000 years ago, Richards said, and "we think they split during the dispersal east, in South Asia or Southeast Asia," possibly 10,000 to 20,000 years before they reached Australia.
"Our results indicate that Aboriginal Australians along with New Guineans have the most ancient unbroken ancestry of any group of people outside of Africa," Richards said.
Along the way, these early human pioneers likely interbred with archaic humans such as Homo longi, H. luzonensis and even "the hobbit" H. floresiensis, according to Richards, but it is currently unclear to what extent modern humans interacted with archaic people in the region.
Adam Brumm, an archaeologist at Griffith University in Australia who was not involved in the study, told Live Science in an email that the research supports the idea that early human movements had a crucial role in the initial peopling of Sahul. "I would put my money, if I had any, on the 'long chronology' model," Brumm said.
This genetic study has wide-ranging implications for the antiquity of Aboriginal people in Australia. "Many Aboriginals believe they have always been in Country," study co-author Helen Farr, an archaeologist at the University of Southampton in the U.K., told Live Science in an email.
"This data supports a really deep heritage for these communities," Farr said, and "it tells of the close links people have had with Country and Sea Country for at least 60,000 years." But it also proves that seafaring knowledge and skills, which are not found in the archaeological record, were key to early humans' survival.
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