The ancestors of Aboriginal Australians and Papua New Guineans diverged from Eurasian populations around 72,000 years ago according to a new DNA analysis of 83 Indigenous Australians from the Wongatha Nation in the North-Eastern Goldfields of Victoria.
The finding supports the idea that humans spread out of Africa in a single event, in the first comprehensive population-level whole-genome study of human genetic diversity in Australia.
The study is the first extensive investigation of Aboriginal Australian complete DNA diversity as prior to this study, only three Aboriginal Australians had had their full DNA sequences described. The researchers found that Aboriginal Australians and Papuans from New Guinea are closer to each other than to any other present-day worldwide populations they looked at, consistent with the idea that they both originating from a common ancestral population which initially colonised the single continent Sahul (Australia, Tasmania and New Guinea).
The timing and route of human population expansion from our evolutionary birthplace in Africa to Europe, Asia and Oceania is hotly debated. Some models suggest that all present-day non-Africans can trace their ancestry back to a single population while others suggest that migration out of Africa took place in distinct waves at different times.
Associate Professor Darren Curnoe is a specialist in human evolution from the School of Biological, Earth & Environmental Sciences at the University of New South Wales and he says this work represents an impressive technical feat and helps fill a major void in understanding the origins of two of the world's great populations -- Indigenous Australians and New Guineans.
"The idea that modern humans left Africa in multiple waves to settle Eurasia has taken on considerable traction of late. I don't think this study will be the final word on this issue, as recent discoveries in places like China cast a big shadow over it," Curnoe says. "This new work broadly shows that Australia was settled only once, without clear evidence for later migrations from far off places like India. This new work might finally mark the death of this unfortunate nineteenth century idea".
Yet the work contains some real surprises, Curnow says, which are cause for concern. "The genetic clock ages they've put on events like the settlement of East Asia and Australia are way too young and out of sync with the evidence from archaeology and the ancient environment of our region. I guess it all comes down to the assumptions you make in your genetic clock, and these are very much up for grabs at the moment, making molecular dates like these rather prone to error."
The research is part of a series of three studies which looked at the genetics diversity from typically understudied regions around the world to provide insight into the migration of modern humans out of Africa.
David Reich and his team of researchers have reported genome sequences of 300 people from 142 different populations, finding that the population that gave rise to all present-day humans began to diverge at least 200,000 years ago, and since then the accumulation of genetic mutations has accelerated by about 5 per cent in non-Africans. A possible explanation for this could be that the time between generations decreased in non-Africans after separation, increasing the rate of change in genetic material.
Eske Willerslev sequenced the genomes of 83 Aboriginal Australians from across the Australian mainland and 25 individuals from the highlands of Papua New Guinea. The data suggests that the ancestors of Aboriginal Australians and Papua New Guineans diverged from Eurasian populations around 72,000 years ago and reveals traces of genetic material from ancient humans such as Denisovans and an unknown hominin group.
Luca Pagani and Mait Metspalu added 379 new genomes from 125 populations focused on European populations to an existing dataset and find that at least 2 per cent of the genome of modern Papuans reflects ancestry from a distinct population that diverged from Africans earlier than Eurasians. This finding provides evidence for an early, distinct wave of human expansion out of Africa, approximately 120,000 years ago, that led to the peopling of Papua New Guinea.
So although these studies fill in some missing pieces in the puzzle of human history, many fascinating questions remain to fully retrace the steps taken by our ancestors as they explored the world.