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Collaboration between the Archaeogenetics Research Group at the University of Huddersfield and the Centre for Maritime Archaeology at the University of Southampton has shed light on the initial settlement of New Guinea and Australia by modern humans, Homo sapiens, refining our understanding of the origins of seafaring and maritime mobility. This was reported by Phys.org, writes UNN.
Details
During the last ice age, when sea levels were significantly lower than today, New Guinea and Australia were parts of a single landmass known as Sahul. It is known that this species, Homo sapiens, evolved in Africa, but there has long been debate both about the timing of the first settlement of Sahul and about the routes by which people first reached this supercontinent.
New research sheds light on migration
New research — a collaborative effort of archaeogeneticists, archaeologists, earth scientists, and oceanographers, published in the journal Science Advances — has shed light on the question of who, where, and when this early maritime migration took place.
It is known that the ancestors of the people of New Guinea and Aboriginal Australians have lived in Sahul for tens of thousands of years, and many Aboriginal Australians believe that they have always lived on their land. However, for Western scientists and archaeologists, the details of global human dispersal have remained controversial. There are two main views on the timing of settlement: the “long chronology,” which suggests the first settlement around 60,000 years ago (60 kya), and the “short chronology,” which advocates for the first arrival around 45–50 kya.
The interdisciplinary team, which included colleagues from the University of Minho in Portugal, La Trobe University in Australia, and the University of Oxford, initially focused on human mitochondrial DNA (mtDNA) genomes to answer this question. mtDNA is found in mitochondria — the “powerhouses” of our cells, located outside the cell nucleus where the rest of the DNA is stored. As a result, it is inherited only through the maternal line, and differences in mtDNA sequences between individuals can be used to reconstruct maternal genealogies in extremely detailed ways.
Genetic analysis and migration routes
The team analyzed nearly 2,500 mtDNA genomes from Aboriginal Australians, New Guineans, and people from the Western Pacific and Southeast Asia. Based on these data, they constructed a phylogenetic tree and examined how the lineages in this tree are distributed among different populations. All DNA gradually changes over time, and the researchers used the rate of these changes — the so-called “molecular clock” — to date the lineages from each region.
The accuracy of this clock was tested by comparing it with islands with known settlement dates in the remote Pacific — data from a recent article in Scientific Reports, prepared by a similar interdisciplinary team involving Professors Richards and Farr and led by Dr. Pedro Soares from the University of Minho.
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Modern humans, Homo sapiens, evolved in Africa, and mtDNA clearly shows that there was only one major successful migration of modern humans out of Africa, which the team dated to approximately 70,000 years ago. The researchers also found that the oldest lineages unique to Aboriginal Australians, New Guineans, or both groups, but not found elsewhere, date back to approximately 60,000 years ago, strongly supporting the “long chronology.”
The origin of the oldest lineages can be traced to Southeast Asia. The team found that while most of them originated in the northern regions of Southeast Asia — northern Indonesia and the Philippines — a significant minority originated in more southern regions: southern Indonesia, Malaysia, and Indochina. This suggests the existence of at least two distinct dispersal routes to Sahul. The northern route lineages spread throughout New Guinea and Australia, while the southern route lineages were limited to southern Australia. Both sets of lineages date to approximately the same arrival time.
Finally, the team validated the results using a detailed re-evaluation of Y-chromosome data (which is inherited paternally) and whole-genome data (inherited biparentally), as well as archaeological, paleogeographical, and environmental evidence, to cover the full range of available evidence.
Challenges and significance of the results
The scientists emphasize that these results were obtained by analyzing the modern diversity of mtDNA and reconstructing past events. In recent years, ancient DNA (aDNA) has become an extremely valuable source of direct information about our past. However, unfortunately, DNA rarely survives in human remains from tropical regions.
In collaboration with the aDNA laboratory at Harvard, the team still obtained DNA from one archaeological sample from the Indonesian Iron Age. This indicated ancient “back” migrations westward — from New Guinea back to Indonesia, but this sample was too late to provide information about the initial settlement.
Nevertheless, the work is of particular importance, because although the new genetic results are well consistent with the archaeological and paleoecological picture, in recent years many geneticists have moved in the opposite direction — towards a “short chronology.”
This argument is based on re-dating, using a different type of genetic clock, the time when archaic Neanderthals met and interbred in the Middle East with the ancestors of modern non-Africans — as a result of which all of them today have about 2% Neanderthal DNA. Some recent results suggest that this happened much later than previously thought — less than 50,000 years ago. Since all non-Africans seem to share this origin, if such a date is correct, the descendants of modern New Guineans and Aboriginal Australians could only have arrived after this time.
However, there is archaeological and fossil evidence of the presence of modern humans in Southeast Asia and Australia dating back at least 60,000 years ago, so proponents of the “short chronology” have to argue that these early pioneers were completely replaced by a later wave of modern humans.
Instead, the results of the new study suggest that modern Aboriginal Australians and New Guineans are descended precisely from those first pioneer settlers who arrived around 60,000 years ago.
