Genetic traces of the mysterious early humans, whose fossil remains have never been found, are still carried by Australian aboriginal people. When exactly did we first leave the continent and was there just one exodus?
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New DNA research from an worldwide team of scientists shows the ancestors of Aboriginal Australians and Papua New Guineans diverged from Eurasian populations between 51,000 and 72,000 years ago and that there is huge genetic diversity among Aboriginals.
“We’re interested in understanding how our species has come to be how it is through the lens of ancient DNA”, said Swapan Mallick, bioinformatics director at Harvard Medical School in Boston and lead author of one of the three studies appearing in the September 22 issue of the journal Nature.
Overall, the evidence shows that the vast majority of modern human ancestry outside of Africa comes from a single exit from Africa, said David Reich of Harvard Medical School, an author of the 142-population paper.
If you’re wondering exactly who the Denisovans were, they were a distinct sub-species of the human family that has been extinct for many thousands of years, like the Neanderthals.
Genetics has been invaluable in understanding this past.
Aboriginal Australians have always been known as one of the oldest surviving distinct populations of our species.
VIDEO: Professor Eske Willerslev, Centre for GeoGenetics, University of Copenhagen, talking about the genetic history of the Australian Aboriginals. It used sophisticated analysis to estimate when ancient populations split off from each other. If two genomes share long stretches with no differences, it’s likely that their common ancestor was in the more recent past than the ancestor of two genomes with shorter shared stretches. The approach can’t reveal every migration out of Africa, just those that left a genetic legacy that has been handed down to this day.
Their research also manages to settle a long-running debate about the structure of African populations at the beginning of the migration.
The third paper out today, which added almost 400 new genomes to an existing dataset, discovered something curious about Papuans: at least 2 percent of the modern Papuan genome comes from a population other than the one that left Africa to set up shop in Eurasia.
SGDP model of the relationships among diverse humans (select ancient samples are shown in red) that fits the data. This indicates that there was substantial substructure of populations in Africa prior to the wave of migration.
Tracing the Papuan and Australian groups’ progress showed that around 50,000 years ago they reached “Sahul”.
Following the move out of the continent, the pioneers must then have journeyed incredibly quickly to Australia.
That was until a few thousand years ago, when they came into contact first with some Asian populations followed by European explorers in the 18th century.
Although the scientific community could’ve guessed that Aboriginal Australians and Papuans diverged from Eurasians, this study puts a timeline on it happening at about 58,000 years ago. One bunch settled in Eurasia and the other continued east until finding Australasia to their liking. The eastern branch further divided into East Asian and Australasian ancestors.
A graphic representation of the interaction between modern and archaic human lines, showing traces of an early out of Africa (xOoA) expansion within the genome of modern Sahul populations. But some other work has turned up potential signs of a previous migration as early as 120,000 to 130,000 years ago. This migration is only visible in the genomes of a separate set of Sahulians sequenced as part of the Estonian Biocentre Human Genome Diversity Panel. But, in the end, the main migration nearly completely overwhelmed that small, early wave, he adds.
They conclude that, like most other living Eurasians, Aborigines descend from a single group of modern humans who swept out of Africa 50,000 to 60,000 years ago and then spread in different directions.
Whatever the reality of the detail of the Out of Africa event, these studies provide some benchmarks for the timings of some of the key events.
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Chris Stringer, head of human origins at the Natural History Museum in London, said the findings would be controversial in the field, adding: “It either means that the behaviours were developed earlier, they developed these behaviours independently, they acquired them through exchanges of ideas with other groups, or the estimated split times are too old”.
