It’s widely accepted that continental Sahul, the combined landmass of Australia, New Guinea and Tasmania, was settled very early in human history. But the exact entry point and timing of ancient human migration into Sahul, which was eventually split by rising sea levels, is a question that has plagued paleoanthropologists. That is until now. And unexpectedly it’s a virus called hepatitis B providing the scientists with some key answers.
“Chronic hepatitis B infection is endemic in the Australian Aboriginal population and is an important cause of morbidity and mortality as a result of liver disease and cancer,” said study authors from the University of Melbourne, the Peter Doherty Institute for Infection and Immunity, Menzies School of Health Research and Charles Darwin University.
“As part of our clinical work in Australia’s Northern Territory, we were seeing many Aboriginal patients with hepatitis B, often with very advanced disease.”
“In caring for these patients, we began investigating which strain of hepatitis B was causing these infections and collected virus samples from people living in over 30 communities across the Northern Territory.”
The team found that hepatitis B virus isolated from these Aboriginal Australians is a unique strain called HBV/C4, which is not found anywhere else in the world.
Not only was every sample they examined carrying HBV/C4, but when they started looking at the HBV/C4 DNA sequences, they noted that the virus sequences had very strong geographical connections to the communities they visited.
In the same way that human genome sequences are used to trace ancient human migration, they hypothesized that they could use hepatitis B DNA to estimate the movement of the people that have carried these viruses over many generations.
Importantly, hepatitis B virus is usually transmitted from mother to child around the time of birth, and therefore the ancestry of the virus, is likely to reflect the ancestry of those carrying it.
To establish this, the team used cutting-edge evolutionary analyses of hepatitis B DNA sequences together with archaeological fossil and human genome data.
The researchers found that the precursor of the modern HBV/C4 virus entered Australia more than 51,000 years ago.
“By combining data of evolutionary rates of the virus and the location of communities in which patients now live, our analyses suggested that there was a more than 60% probability that the HBV/C4 virus entered Australia through either the Tiwi Islands or East Arnhem regions in Australia’s far north,” they said.
“HBV/C4 then separated into two groups; one in the northwest region, and the other in the central eastern region of the Northern Territory.”
“Strikingly, the two groups share a similar geographical distribution to the two main divisions of Aboriginal Australian languages spoken in Australia today.”
The study was published in the journal Molecular Biology and Evolution.
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Lilly K.W. Yuen et al. Tracing Ancient Human Migrations into Sahul Using Hepatitis B Virus Genomes. Molecular Biology and Evolution, published online February 19, 2019; doi: 10.1093/molbev/msz021