Genomic insights into Aboriginal Australians and first human migrations

Two new genomics studies have shed light on the earliest migrations of humans by showing that the ancestors of present-day Aboriginal Australians left Africa around 70,000 years ago, which is at least 24,000 years before the migration that gave rise to present-day Europeans and Asians.

This suggests that Aboriginal Australians represent one of the oldest living populations of humans in the world, and almost certainly the oldest outside Africa.

The first of the studies, led by Morten Rasmussen from the University of Copenhagen and published in Science, was conducted by sequencing the DNA from a lock of hair donated to a British anthropologist by an Aboriginal man from the Goldfields region of Western Australia in the early 20th century.

While the DNA had degraded somewhat, researchers were still able to sequence and assemble most of it and compare it to the genomes of other populations around the world.

The DNA showed no traces of the signature genetic fingerprints of modern European and Asian, suggesting Aboriginal Australians left Africa in the first great human migration from the cradle of humanity.

Aboriginal Australians therefore descend directly from the earliest modern explorers, people who migrated into Asia before finally reaching Australia about 50,000 years ago. In showing this, the study establishes Aboriginal Australians as the population with the longest association with the land on which they live today.

The history of Aboriginal Australians plays a key role in understanding the dispersal of the first humans to leave Africa. Archaeological evidence establishes modern human presence in Australia by about 50,000 years ago, but this study re-writes the story of their journey there.

Previously, the most widely accepted theory was that all modern humans derive from a single out-of-Africa migration wave into Europe, Asia, and Australia. In that model, the first Australians would have branched off from an Asian population, already separated from the ancestors of Europeans.

However, this study shows that when ancestral Aboriginal Australians begun their private journey, the ancestors of Asians and Europeans had not yet differentiated from each other. Once they did, some 24,000 years after the first Australians had begun their explorations, Asians and remnants of the ancestral Australians intermixed for a period of time.

“It definitely strongly supports the idea that Aborigines were an early and separate wave of human expansion Out of Africa, before the subsequent wave that established Europeans and Asians,” said Professor Alan Cooper, Director of the Australian Centre for Ancient DNA at the University of Adelaide.

“This has long been thought to be the case, due to the very early archaeological signs of Aboriginal presence in Australia (~50 kyr) and existing genetic data, but the highly-resolved view available from a genomic sequence is a really valuable contribution.

“While the information is only from a single individual, it provides a powerful view of the common, shared heritage of the movement of the ancestors of modern Aboriginal populations from Africa around half the world to Australia – which is one of the most important and poorly understood stories of human history.”

The second study, led by David Reich, Professor of Genetics at the Harvard Medical School and published in the American Journal of Human Genetics, found that the forebears of Aboriginal Australians interbred with another archaic human population called Denisovans, who ranged from Siberia to Southeast Asia.

This also reinforces the notion that there were two great migrations of early modern humans out of Africa.

“Denisova DNA is like a medical imaging dye that traces a person's blood vessels,” said Reich. “It is so recognisable that you can detect even a little bit of it in one individual. In a similar way, we were able to trace Denisova DNA in the migrations of people. This shows the power of sequencing ancient DNA as a tool for understanding human history.”

“This study will be of great interest to a wide range of researches in anthropological genetics and molecular biology,” said Professor Jun Wang, another head of the study and Executive Director of BGI.