Human skeletons and archaeological remains in Australia can be traced back nearly 50,000 years before the trail disappears. Before then, apparently, Australia was free of humans.
So how did people get there, and when? Where did humans first arrive on the continent, and how did they spread across the entire landmass?
Answers to some of these questions are stored in the DNA of Aboriginal Australians. A genetic study of 111 published on Wednesday last week offers an interesting — and, in some respects, unexpected — view of their remarkable story.
All living Aboriginal Australians descend from a single founding population who arrived about 50,000 years ago, the study says.
They swept around the continent, along the coasts, in a matter of centuries. And yet, for tens of thousands of years after, those populations remained isolated, rarely mixing.
The DNA used in the new study comes from Aboriginal hair collected during a series of expeditions between 1926 and 1963. The Board for Anthropological Research at the University of Adelaide sent researchers to communities across Australia, where they collected vast amounts of information about Aboriginal languages, ceremonies, artwork, cosmologies and genealogy.
Many Aboriginal Australians today no longer live where their ancestors did.
During the 1900s, the Australian government forcibly removed many from their traditional lands and separated children from families. Many Aboriginal Australians moved to cities far from where they grew up.
Thanks to the subjects’ age and detailed records, scientists suspected the hair samples might offer a glimpse of the pre-colonial past.
“It seemed obvious that this collection is perhaps the best way to reconstruct Australian history,” said Alan Cooper, a pioneer in ancient DNA studies at the University of Adelaide.
He and his colleagues first sought consent for the tests from the descendants of the people whose hair samples had been collected. They traveled to Aboriginal communities, spending several days talking to family members to address their concerns.
All but one of the families they visited gave them permission to run the study.
Cooper and his colleagues knew extracting DNA would not be easy. Over the decades that the hair had been in storage, the genetic traces may have broken down beyond recognition.
Making matters worse, the hair had been cut with scissors. The best way to get genetic material from a strand of hair is to pull it out at its DNA-rich root.
Given these uncertainties, the scientists decided to increase the odds of success by searching for abundant mitochondrial DNA, which is situated outside the cell nucleus and is inherited solely from the mother.
Eventually, the scientists managed to piece together all the mitochondrial genes in each of the hair samples.
By comparing the Aboriginal sequences to DNA from other parts of the world, the scientists determined that they all belonged to a single human lineage, indicating that all Aborigines descended from a single migration to the continent.
Mitochondrial DNA gradually accumulates mutations at a roughly regular rate, ticking like a molecular clock. By adding up the mutations in the hair samples, the scientists also estimated that their owners all descended from a common ancestor who lived about 50,000 years ago. That finding fits nicely with the estimated ages of the oldest archaeological sites in Australia.