An international team of scientists, which includes Australian Aboriginals, have produced the first comprehensive population study using full genomes of 83 Aboriginal Australians and 25 individuals from Papua New Guinea.
Both peoples are part of the same branch of our family tree, they conclude.
“We show that all Australian Aboriginals descend from a population that became separated from other human populations approximately 51,000 to 72,000 years ago,” says co-author Rasmus Nielsen, a professor with the University of California, Berkeley, USA and the University of Copenhagen, Denmark.
The new results are published in the scientific journal Nature.
Aboriginal studies are politically sensitive
The scientists first mapped the genome of a single Aboriginal individual using a sample of 100 year-old hair, archived at the Leverhulme Centre for Human Evolutionary Studies in Cambridge, UK.
Their analysis showed that Aboriginals are one of the oldest living populations outside of Africa. This made the scientists want to analyse more samples from living people to map the Aboriginals’ unique genetic history.
But the project has been politically sensitive, not least because some Australian scientists expressed doubts that Aboriginal Australians were indeed the first people to inhabit the country.
“Australian scientists said it was impossible. ‘No, no, no, it’s so politically dangerous,’ they said. But that simply wasn’t our experience. Most people have been really positive,” says co-author Professor Eske Willerslev from the Center for Geogenetics at the University of Copenhagen in Denmark.
A big job to obtain samples
Before they could start the science, Willerslev and colleagues took steps to meet with Aboriginal groups to first gain their permission for the study.
Native Australians have long been sceptical about “the white man’s” science and have forbidden scientists from collecting genetic material. The ice was finally broken with the results of the 100 year-old hair sample.
“I think that a lot of them had heard about the study and were interested,” says Willerslev.
It took Willerslev and his team many years to travel round the country, assisted by Professor David Lambert, from Griffith University in Queensland, Australia. Eventually they established contacts with Aboriginal groups and gained their permission to take samples for DNA analysis.
Together with samples already obtained from habitants of Papua New Guinea, the scientists set out to map the two groups’ genetic history.
First Australians came from Africa
Australia has long played a central role in the history of modern human migration out of Africa.
We all originate from Africa and some of the oldest archaeological finds of modern humans outside of Africa are some 40,000 to 50,000 year-old skeletons from Mungo in Australia. Almost as far from Africa as you can get.
It suggests that the first people to leave Africa followed an express route along the coast that lead them all the way to Australia.
Language and tools are witnesses to migration from India
How many waves of migration there were from Africa, and whether Aboriginal Australians are the descendants of the first humans to reach Australia, were contentious topics.
Language researchers have estimated that 90 per cent of all Australian Aboriginals are a part of a language group called Pama-Nyungan, which according to researchers is no more than 6,000 years old.
And archaeological discoveries of stone tools that date back to 6,000 to 7,000 years ago point towards a migration of people from India. But the DNA tells a very different story.
“Let me say straight away that we’ve found absolutely no evidence for that [migration from India]. We see a long period of isolation in Australia up until a couple of thousand years ago,” says Willerslev.
Two very different groups
The genetic evidence suggests that both Australian Aboriginals and Papuans came out of Africa in a single group. But they split away from this group of Africans, around 70,000 years ago and followed the coast east, past India and on to Indonesia.
They reached Australia around 50,000 years ago, which at that time was connected to Papua New Guines, as part of a larger continent called Shaul.
Aboriginals and Papuans separated around 25,000 to 45,000 years ago, at the same time that Europeans and Asians split into two groups probably around the Middle East.
“Even though Aboriginals and Papuans are close relatives, they are just as different as the Han Chinese are to Danes,” says Willerslev.
Cultural Barriers kept them apart
The landmass between Papua New Guinea and Australia was submerged around 10,000 years ago, after the last ice age.
“It’s perhaps a little surprising that Aboriginals and Papuans began to diverge from each other,” says Nielsen.
Scientists do not know why they diverged from one another, but one factor could have been cultural barriers.
Willerslev and colleagues also discovered large variations between Aboriginal groups. Their genetics reveal that the indigenous population had already begun to diverge around 32,000 years ago, when the continent’s central desert began to grow and isolated the different groups to the east and west of this vast desert.
These genetic differences are further evidence for just how long, Aboriginals have inhabited Australia.
Mysteries surrounding language and tools
The discrepancies in time-scales between the genetic evidence and archaeology and language history can be rectified.
“It’s really interesting that we see a population growth around 6,000 to 7,000 years ago, which is evidence for a gene-flow spreading from the northeast to the rest of the continent. But it’s mysterious,” says Willerslev.
These people could have spread Pama-Nyungan languages and the new stone technology and culture to the rest of Australia.
Traces of an unknown group of humans
Within all of our genomes are traces of our ancestors’ interactions with earlier groups of humans such as Neanderthals. But the Australian’s DNA suggest that they must have met another, previously unknown group shortly after leaving Africa.
The scientists also discovered traces of DNA that are similar, but still different from other known groups of hominids.
“The DNA is more closely related to Denisovans than Neanderthals, but at the same time it is very different from the Denisovan genome,” says Willerslev.
It is likely that the DNA comes from a third group of hominid that survived until around 50,000 years ago. The discovery gives a whole new picture of our ancestral landscape.
“Although evidence for gene flow from an unknown hominin group is tentative, it highlights the potentially surprising things that can be learnt from a comprehensive sampling of human genomic variation,” write biologists Serena Tucci and Joshua Akey from the University of Washington, USA, in a commentary for Nature.
Jakobsen, Rasmus Kragh. 2016. “DNA confirms Australian Aboriginals are the oldest civilisation still around on Earth”. Science Nordic. Posted: October 2, 2016. Available online: http://sciencenordic.com/dna-confirms-australian-aboriginals-are-oldest-civilisation-still-around-earth