Originally published 2016-10-21.
In September 2016 the journal Nature published three large studies of human DNA that, together, told a striking story about Australia. The biggest genomic study of Aboriginal Australians up to that point concluded that today's Aboriginal peoples descend from the first humans to reach the continent, and that their ancestors have lived there continuously for around 50,000 years. That makes Aboriginal Australians one of the oldest continuous cultures anywhere on Earth, and very likely the oldest.
The studies also shed light on a much bigger question: how and when modern humans left Africa and spread around the world. Below we explain what the research found, what it did not prove, how archaeology has since pushed the timeline even further back, and why Aboriginal communities saw the findings as confirming what they had long known.
What the 2016 genome study found
The central paper, A genomic history of Aboriginal Australia, was led by Anna-Sapfo Malaspinas, with the project conceived and headed by Eske Willerslev of the University of Copenhagen and David Lambert. The team sequenced high-quality genomes from 83 Aboriginal Australians, all speakers of Pama-Nyungan languages, and 25 Papuans from the New Guinea Highlands. Samples were collected in collaboration with local communities.
Their main conclusions:
- The ancestors of Aboriginal Australians and Papuans split from the ancestors of Europeans and Asians somewhere between about 51,000 and 72,000 years ago, after a single main dispersal out of Africa.
- Aboriginal Australians and Papuans then diverged from each other between roughly 25,000 and 40,000 years ago, long before rising seas separated New Guinea from Australia around 8,000 to 10,000 years ago.
- All the Aboriginal Australians sampled descend from one founding population, which later differentiated into regional groups between about 10,000 and 32,000 years ago.
In other words, there is no genetic sign that Aboriginal Australians were replaced by a later wave of newcomers. The people who arrived first are the ancestors of the people who live there now.
Willerslev summed up the scientific gap the work was filling in a line widely quoted at the time: "This story has been missing for a long time in science."
The first great ocean crossing
Even when sea levels were much lower during the last Ice Age and Australia, New Guinea and Tasmania formed a single landmass called Sahul, there was never a land bridge from Asia. Reaching Sahul meant crossing open water between islands in what is now Indonesia, with some gaps of tens of kilometres.
That is why researchers describe the ancestors of Aboriginal Australians and Papuans as among the earliest humans to make deliberate sea voyages. They must have built watercraft, planned for the journey and travelled in groups large enough to found a lasting population. It is a remarkable achievement for people living tens of thousands of years before farming, writing or metal tools.
Ancient relatives in the family tree
On their way across Asia, the ancestors of Aboriginal Australians and Papuans met and had children with other kinds of humans. Like all people outside Africa, they carry a small share of Neanderthal DNA. They also carry a larger share from Denisovans, a group known mainly from fossils in Siberia and Tibet.
Some news coverage in 2016 reported that around 4 per cent of Aboriginal genomes might come from an unidentified archaic human. The paper itself frames its findings mainly in terms of Denisovan and Neanderthal ancestry, so that figure is best read as a tentative interpretation rather than a settled fact.
The study also found a population expansion in north-east Australia within the past 10,000 years, with limited gene flow to the rest of the continent. That pattern fits the spread of the Pama-Nyungan language family, which today covers most of mainland Australia, suggesting that languages and ideas often travelled further than people did.
Two companion studies, and a disagreement
Two other papers appeared alongside the Aboriginal study. The Simons Genome Diversity Project, led by Swapan Mallick and David Reich at Harvard Medical School, analysed 300 genomes from 142 populations. It found that all non-African ancestry is consistent with a single founding population, and that Aboriginal Australians, Papuans and Andaman Islanders carry no substantial ancestry from an earlier exit. It also found that some human populations were already separated around 100,000 years ago, before the archaeological signs of so-called modern behaviour such as cave art appear. Coverage of the study reported that the authors saw no single "magic mutation" that suddenly made us human.
The third paper, led by Luca Pagani of the Estonian Biocentre, looked at 483 genomes from 148 populations and reached a partly different view. It agreed that a major dispersal from Africa occurred around 75,000 years ago, but it detected a faint signal in Papuans: at least 2 per cent of their genome appears to come from an earlier, largely extinct expansion out of Africa, possibly as long as 120,000 years ago.
So the three studies agreed on the big picture while disagreeing on the details, which is common in a fast-moving field.
Archaeology pushes the date back
Genetic dates depend on assumptions about mutation rates and generation times, and other scientists were quick to point this out. Darren Curnoe of the University of New South Wales told reporters: "I don't think this study will be the final word on this issue."
He was right. In July 2017 a team led by Chris Clarkson of the University of Queensland reported in Nature new dates from Madjedbebe, a rock shelter on Mirarr country surrounded by Kakadu National Park. The excavation, carried out in partnership with the Mirarr Traditional Owners, showed people had been living there for at least 65,000 years, well beyond the 47,000 years some archaeologists had argued for.
The lowest layers held more than 10,000 artefacts, including the oldest known ground-edge stone axe technology in the world, Australia's oldest seed-grinding tools and large amounts of ground ochre. Today most researchers accept that people reached Australia somewhere between about 50,000 and 65,000 years ago, and the debate continues as new sites are dated.
What "oldest continuous culture" does and does not mean
The phrase is often misunderstood. It does not mean Aboriginal cultures stayed frozen for 50,000 years. Aboriginal societies developed hundreds of languages, managed landscapes with fire, built eel traps and stone houses, traded over long distances and adapted to dramatic climate change, including the end of the Ice Age and rising seas.
What it does mean is that there has been an unbroken line of people, and their knowledge, connected to the same land from the earliest settlement to today. Genetics can confirm the continuity of ancestry; it cannot measure the richness of a culture, and it is no substitute for the knowledge held by Aboriginal communities themselves.
Aubrey Lynch, an elder from the Goldfields region of Western Australia, put it simply when the 2016 results were announced: "This study confirms our beliefs that we have ancient connections to our lands."
Why this research matters
For much of the twentieth century, some writers suggested that Aboriginal people were relatively recent arrivals, or that an earlier population had lived in Australia before them. These ideas were used, directly or indirectly, to weaken Aboriginal claims to land. The 2016 genomes, together with the archaeology, firmly contradict them.
The research also shows how genetic studies can be done better: with community involvement in collecting samples, with results returned to the people concerned, and with humility about what DNA can and cannot tell us. The best picture of the deep past comes from combining genetics, archaeology, linguistics and Indigenous knowledge rather than relying on any one of them alone.
Sources: Malaspinas et al., A genomic history of Aboriginal Australia (Nature, 2016); Mallick et al., The Simons Genome Diversity Project (Nature, 2016); Pagani et al., Genomic analyses inform on migration events during the peopling of Eurasia (Nature, 2016); University of Queensland, July 2017: Kakadu find confirms earliest Australian occupation; Fiona MacDonald, ScienceAlert (September 2016), quoting interviews first given to The Guardian, The Verge and Gizmodo Australia.
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