Understanding the history of Aboriginal Australians, their origins and how their population changed over some 50,000-plus years has always been an enormous challenge.
Many Aboriginal people have their own origin stories. Gudjugudju, a Gimuy Yidinji Elder from the rainforest people around Cairns, says:
The story which has been passed down from generations tells of three migrations that have occurred over many thousands of years, one of us coming to this ancient land first, then another at a period after the last Ice age which saw the formation of the Great Barrier Reef, the other is of a migration out of Cairns that went back through the Cape into the Torres Strait to PNG and further.
Equally, scientific narratives of Aboriginal origins have presented different accounts. But these have been difficult to establish in part due to the difficulty and limitations of the science involved.
It’s also because of the social context that both science and archaeology work in within Australia.
The first few decades of modern archaeological research into Australia’s ancient past was conducted with very little to no involvement of Aboriginal Australian people.
This was followed by decades of debate over ownership of the past. Initial DNA research proposals floundered because little to no consultation was undertaken.
A new period of community based research with Aboriginal people was forged through the sensitive and highly consultative approach pioneered by geneticist Sheila Van Holst Pellekaan. Her work with Aboriginal people set the standard for later scientific studies in Australia.
We can now provide an example of work undertaken in partnership with Aboriginal Australian people from all parts of Australia, from the deserts to urban and regional centres. The details of the research are published today in Nature.
The First Australians
Our results show very clearly that Aboriginal Australian people living today are the descendants of the First People to enter Australia, who lived between 25,000 to 40,000 years ago.
There is substantial evidence of admixture or intermixing with Asian, Oceanic and European people within the last 200 years. But in the Aboriginal DNA is an ancient story of migration into this continent, far deeper in time than any other population group has so far revealed.
It shows ancient contact and gene flow between the ancestors of the First Australians and now extinct populations of Neanderthals and Denisovans. This is very similar to the gene flows reported between Neanderthals, Europeans and Asians.
Our paper supports the results of earlier genomic research. This includes the foundational study on the first Aboriginal Australian genome from Western Australia and ancient DNA recovered from fossil remains from Lake Mungo.
Our research discounts the political agenda of some individuals who have claimed that Aboriginal Australians may not have been the First Australians.
The research also helps clarify a number of key points that archaeologists have been debating since the 1960s, such as where the ancestors of Aboriginal Australian people likely first entered the continent.
The first migration
There has been considerable debate as to whether the First Australians took the northern route (through Papua and then down into Cape York) or a more southerly route, crossing from Timor into north-western Australia.
Our evidence reveals a picture of population expansion from north east Australia.
Around 10,000 years ago, sea levels rose and the land bridge between Papua and Cape York was flooded. Based on this, the genetic separation of Papuans and Aboriginal Australians was generally believed to have been initiated after this time.
But using large-scale genome data from Australians and Papuans we estimate the time of divergence between the two groups to be 37,000 years ago. This is much earlier than previously predicted.
This also suggests that barriers to intermarriage between Australia and Papua occurred much earlier than the creation of the barrier of Torres Strait.
Interestingly a significant barrier to gene flow within Australia also seems to have occurred at the time of the last great ice age, known as the Last Glacial Maximum (LGM).
East and west Australians
We see significant divergence between Aboriginal Australian people of north east and south west Australia. These groups are more genetically different than, for example, Native Americans and Siberians are from each other.
They are all Aboriginal Australians of course, but the onset of the LGM seems to have limited gene flow between east and west. As a result, the formation of a different population structure began some 31,000 years ago.
Further subdivisions among eastern and western Aboriginal Australians appeared to have occurred later. The phylogenetic relationships based on our genetic data correlated well with the divisions based on the Aboriginal (Pama-Nyungan) languages spoken by the people.
Some researchers have maintained for many years that the archaeological record shows significant population expansion in the last few thousand years before the arrival of Europeans.
Other archaeologists have disagreed, stating that demographic expansion can be a very difficult thing to prove from a record of carbon dates, stone tools and shell middens.
These signatures are very prone to destruction by such things as erosion and sea level change. Much of the first coastline initially colonised by the First Australians now lies beneath the waves, locked in a drowned landscape.
The genetic evidence for population increase in north east Australia, one area that some archaeologists have argued was subject to significant population expansion, is actually earlier than expected. It seems to begin some 10,000 years ago, which is several thousand years earlier than evidence provided by archaeology.
What we did find was unique genetic variations specific to Aboriginal Australians that might have given them an improved ability to withstand cold and dehydration – potential adaptations to life in the desert.
Previous studies have shown the potential of DNA in understanding the ancestral relationships of Aboriginal Australian people. Genome sequencing in the past few years has revealed a far more complicated picture than first thought.
We can now tackle questions that have been debated for decades using the actual evidence from the biology of the First Australians.
It is crucial that we continue to make sure that such research is done in partnership with Aboriginal Australian people.
As noted by one of the key researchers in the project, Dr Craig Muller, who said:
We have developed close relationships with many individuals throughout the project, and collaborated closely with Aboriginal Elders in each language group who provided important cultural information. The Elders also guided us to the appropriate people to participate.
A great example of how things have changed since the early years is that there are now new generations of young Aboriginal Australian researchers undertaking DNA research.
In parallel is the interest shown by many indigenous groups who are interested in this research and keen to partner with us. This suggests a wonderful future might lie ahead.
First published: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature18299.html