LONDON: For the first time, the genome of an Aboriginal Australian has been sequenced, shedding new light on the journey that early humans took out of Africa as they spread across the globe.
The discovery, which was made by an international team of scientists and is published today in the journal
Science, contradicts the accepted wisdom that modern humans descend from a single wave of migration out of Africa.
Instead, it seems that the ancestors of Aboriginal Australians set off some 24,000 years before the ancestors of modern populations in Asia and Europe in an earlier migration wave.
Until now, the history of Aboriginal Australians has been hotly debated. "We know that modern humans evolved in Africa, but there is not agreement about how Australia was populated," said evolutionary geneticist and co-author Rasmus Nielsen from the University of California, Berkely.
Alternate migration theories
"One theory assumes that modern Aboriginal Australians descend from the same migration wave the Asians and Europeans descend from," he said.
The alternative hypothesis is that there were two major waves of dispersal - a first a wave that relatively quickly reached Australia, and then a second wave that settled Europe and most of Asia, and replaced the descendants of the first wave in these regions.
It was also unclear whether the modern day Aboriginal Australians descended from the first modern human individuals settling Australia about 50,000 years ago, or if they descended from later settlers, Nielsen said.
Aboriginal ancestors from first wave
The new study concludes that humans probably dispersed in two waves out of Africa, with the ancestors of Aboriginal Australians forming the first wave of explorers who spread via Asia around 70,000 years ago.
It also suggests that Aboriginal Australians do indeed descend from the very first settlers to reach Australia around 50 thousand years ago, highlighting the long association with the land they live on today.
Nielsen and his team sequenced the DNA from a 100-year-old lock of hair of donated by an Aboriginal man from the southern region of Western Australia in the early 20th century. They chose such an old sample because they wanted to make sure the man was of Aboriginal descent.
"We wanted to exclude the possibility that the DNA we analyzed was from an individual who could count both Europeans and Aboriginal Australians among its recent ancestors," Nielsen said.
Hair holds ancestral clues
They then compared the DNA from the hair sample to Asian, African, and European genomes to see how much DNA they shared, and to determine when their common ancestors would have branched from one another.
The results suggest that the Aboriginal Australian donor of the hair sample probably descended from an earlier, independent wave of out-of-Africa dispersal which branched off from the ancestors of other modern human populations about 64-70,000 years ago.
The ancestors of modern Asian and European populations separated about 24,000 years later. However, can the results from one individual be applied to an entire population?
According to Nielsen, the DNA of a single individual can tell us much about ancestral populations, but there is still a chance that the ancestral history of other Aboriginal Australians is different from the history of this person, and further research is needed before we an be sure.
Does it account for Aboriginal diversity?
Sheila van Holst Pellekaan, a geneticist from the University of New South Wales in Sydney, who works to explore genetic variability in Aboriginal populations, is also cautious.
"Even with this study, we cannot conclude that it is representative of the great many language groups in Australia," she said.
However, the research adds greatly to the body of knowledge already out there and supports what we already know, she said: "that the first Australians arrived very early in the dispersal of humans and are one of the oldest living indigenous populations outside Africa."
She continued: "The study also adds to the story of human arrivals in Asia, important to the whole region of Oceania."
Van Holst Pellekaan also commended the authors for engaging with representatives from the community in question to publish this report and acquire consent. "This is crucial, since there is still considerable resistance to genetic research from many Aboriginal Australians."
Now with one Aboriginal genome sequence available, researchers will also be able to look for genetic variation that could influence health and wellness, she said.
Aboriginal genome - About damn time
Reply With Quote
