By human skeletons and archaeological finds in Australia, you can trace the history of up to 50,000 years before the trail disappears. Up to this point, apparently, there were no people in Australia. How did the people get there and when? When did people first arrive on the continent and how did they spread throughout the continent? The answers to these questions can be found in the DNA of Australian Aboriginal people. A genetic study of 111 Aboriginal Australians, published last week, offers an interesting, and in some respects unexpected, view of their remarkable history.
All of the living indigenous Australians are from a single population of founders who arrived about 50,000 years ago, the study shows. They settled on the continent, along the coasts, for many centuries. And yet, for tens of thousands of years after that, these populations remained isolated and mixed very seldom.
The DNA used in the new study is taken from aboriginal hair collected during expeditions that took place from 1926 to 1963. The Council for Anthropological Research at the University of Adelaide sent researchers to communities throughout Australia, where they collected a wealth of information about indigenous languages, ceremonies, works of art, cosmology and genealogy.
Many aboriginal Australians today no longer live where their ancestors lived. In the 1900s, the government of the country forcibly removed many of their traditional lands and separated children from their families. Many Aboriginal Australians moved to cities far from the places where they grew up.
Thanks to the age of the subjects and the detailed reports, the scientists decided that hair samples can give the best idea of the pre-colonial past. “It seemed obvious that this collection is perhaps the best way to restore Australian history,” says Alan Kupir, a DNA researcher at the University of Adelaide.
At first, he and his colleagues asked for consent from the descendants of people whose hair samples were collected. They traveled to Aboriginal communities, spending several days in communication with family members to help them solve problems. All but one family they visited gave them permission to conduct research.
Dr. Cooper and his colleagues knew that extracting DNA would not be easy. For many decades, while the hair was stored, genetic traces could collapse beyond recognition. Worse, the hair was cut with scissors. The best way to get genetic material from a strand of hair is to pull it out with a rich DNA root.
Given these uncertainties, scientists decided to increase the chances of success by seeking a rich mitochondrial DNA that is outside the cell nucleus and inherited solely from the mother. In the end, scientists managed to collect together all the mitochondrial genes in each of the hair samples.
Comparing aboriginal sequences with DNA from other parts of the world, scientists determined that they all belong to the same human ancestry, which means that all aborigines originated from one migration to the continent.
Mitochondrial DNA gradually accumulates mutations at approximately the same rate, ticking like a molecular clock. Summarizing the mutations in the hair samples, the scientists also calculated that their owners all descended from a common ancestor who lived about 50,000 years ago. This finding perfectly agrees with the estimate of the age of the oldest archaeological sites in Australia.
The mitochondrial tree also provided clues to how people are spreading across the continent.
Fifty thousand years ago, the sea level was so low that Australia and New Guinea formed a single continent. People moved from Southeast Asia to this continent; Some settled in present-day New Guinea, others moved further south to Australia.
They kept the coastlines until they reached South Australia about 49,000 years ago. But as soon as this large resettlement was completed, according to a new study, the ancestors of modern Aborigines sat at their homes for tens of thousands of years.
Mitochondrial DNA does not contain evidence that these populations were mixed in any significant way, which surprised scientists. “We expected that in all places there would be a very diverse mix of people,” says Cooper.
This is not a model of migration, which is documented by genes on other continents. In Europe, for example, new peoples settled every few thousand years, mixing with the societies they encountered.
The difference is visible in agriculture, says Cooper. Unlike Africa, Asia and Europe, Australia did not experience the rise of agriculture several thousand years ago. “If you do not have cheap carbohydrates, you can not increase the population,” he says.
The population grew on other continents, but was often at risk of catastrophic crop failures. When this happened, there was only one answer: mass migration.
In Australia, the Aborigines did not rely on the harvest and lived as nomads in certain regions. They never felt the need to cross the continent.
“This is indeed very surprising, but at the same time undeniable,” says Stefan Schiffels, a population geneticist from the Max Planck Institute for Human History in Germany, who did not participate in the study. “The data speak about this.”
Peter Bellwood, an archaeologist at the Australian National University, also did not take part in the study, said that most of the new data corresponds to archaeological data. But it was difficult for him to understand how the Aboriginal Australians could have stayed sedentary for so long.
He points to the tools that many aboriginal cultures shared over long distances, as well as the seven languages spoken by many indigenous peoples. Dr. Bellwood doubts that they could spread so far without humans.
“If people do not move, why do they need languages and tools?” He says.
Dr. Schiffels and other scientists expressed the opinion that there are no important details of Australian history in mitochondrial DNA. DNA in the nucleus of each cell coming from both parents can give a clue to a wider range of data.