Analysis of mitochondrial DNA from nearly 2,500 sequences suggests that two lineages arrived from Sunda to Sahul via different routes, implying that humans knew how to sail the open seas even then.
Dr. Yonat Ashchar, Davidson Institute website, the educational arm of the Weizmann Institute
When did the first people arrive in Australia?
Over the past century, the answers to this question have changed repeatedly. Initially, when it was already clear that humans evolved in Africa and went out from there to colonize the rest of the world, it was assumed that Australia was among the last places humans reached: after all, it is very far from Africa. In addition, to reach this continent, there is no choice but to cross many kilometers of open and deep sea, so the first Australians would have had to know how to build and sail boats or rafts. It therefore makes sense that the colonization of Australia occurred late, after the other continents had already been settled – not only Asia and Europe but also the Americas, which in the past could Reach them by walking from Siberia through Beringia, the land area that is now beneath the waters of the Bering Strait.
Then, in the second half of the last century, Dating methods have improved. of archaeological finds, and results began to come in that did not fit with this story. Settlement sites in Australia and New Guinea, the large island to the north of the continent, were dated to 40 and 45 thousand years before our era, dates that placed them among the earliest sites to which humans migrated after leaving Africa. Since the prevailing hypothesis is that humans left Africa only 50 to 70 thousand years ago, it seems unlikely that they managed to reach Australia as early as 40 thousand years ago, but studies in recent years suggest that settlement occurred even earlier.
In 2017 A study was published In it, researchers used new dating methods and concluded that a site in northern Australia was inhabited as early as 65 years ago. But not everyone was quick to embrace these conclusions. About a year ago A study was published who examined the issue from a genetic perspective, and relied on the fact that after humans left Africa, they Interbred with Neanderthals, and Neanderthal genes are still present in our genomes today. These researchers calculated, based on the mutations that have accumulated since then, that this gene exchange with Neanderthals took place less than 50 years ago, in the population from which all non-African humans originated.
Australians also carry the same Neanderthal genes, so they too are descendants of the same population, which only split into different groups after gene exchange with Neanderthals. If this happened less than 50 years ago, they could not have been isolated in Australia 65 years ago.
Now being published New research, which is also based on genetics, which actually supports the hypothesis that humans arrived in Australia very early, about 60 years ago.
A 4,000-year-old rock painting of Wandjina, the rain-bearing entity in Aboriginal mythology, Mount Elizabeth Station, Western Australia | Source: Graeme Churchard, flickr
When did the dynasties split?
The researchers used In mitochondrial DNA, that is, the genetic material in mitochondria – these are tiny organelles found inside our cells, and are responsible for producing energy. These organelles have their own DNA, separate from our main DNA, which is found in the cell nucleus. This DNA also undergoes random changes over time, most of which do not affect its activity. As such, the mitochondrial DNA of different people is not the same, and it can be used to build a family tree. Or rather, to build the female side of the family tree: since we We get our mitochondria from our mother., and not from both parents like nuclear DNA.
To build the gene tree of the Australian people, the researchers obtained 973 new mitochondrial DNA sequences from people living in Australia, New Guinea, other islands in the region, and Southeast Asia. They also used an additional 1483 sequences collected in previous studies.
Once they had constructed the family tree, the researchers could track the changes in DNA over time. The rate at which mutations occur is fairly constant, and by counting the changes between different groups, they could deduce when they split off. The researchers concluded that the Australians and New Guineans split off from the islanders and Asians about 60 years ago.
The first seafarers
In those distant days, tens of thousands of years ago, the sea level was much lower. As a result, New Guinea to the north of Australia, and Tasmania to the south, were not separate islands but were connected to the mainland. That Australia-plus continent is called Sahul. In Southeast Asia, the borders of the continent also looked very different: some of the islands of Indonesia – Borneo, Sumatra, Java and Bali – were not yet islands, but connected to the Malaysian peninsula and the entire continent. This area is called Sunda.
To colonize what is now Australia, early humans had to travel from Sunda to Sahul. Mitochondrial DNA research has revealed that there were two main lineages of people who did this and colonized Sahul, each arriving on the continent by a different route – but at roughly the same time.
The first group migrated via what is known as the northern route, from the Philippines via the Indonesian island of Sulawesi and other islands to New Guinea, which was then part of Sahul. The second group arrived via a more southern route, from the southeastern tip of the Sunda Islands to the southern Indonesian Islands and Timor, and from there to the area in Australia where the city of Darwin is now located, roughly halfway along the northern coast of the continent. From these locations, both lineages continued and spread across Sahul to Tasmania in the south.
The people who reached Sahul via Timor had to cross the sea between it and Australia. At that time, the journey was much shorter than today, as low sea levels exposed large areas of land that are now covered by water. Still, the first Australians had to cross about 100 kilometers of deep sea. If the researchers are right, and they did so as early as 60,000 years ago, this may be the earliest evidence of the use of boats not just near the coast, and not just for moving between nearby islands, but for migrating over longer distances.
The movement of the lineage that came from the northern route to the northeastern coast of Australia is shown in purple; and the migration route of the lineage that advanced along the southern route towards the central northern coast of Australia is marked in red. The additional land route that existed 60 years ago is marked in brown, and the land route today is in white | Source: Liat Peli based on the illustration by Arip Rahman 27, Shutterstock
Waiting for ancient DNA
The question of “when did the first people arrive in Australia” still has no universally agreed-upon answer. The new study provides support for the hypothesis of an “early arrival,” 60 years ago or more, but that is not yet the final word. The researchers also plan to examine nuclear DNA, which is much larger and therefore contains more information than mitochondrial DNA.
The thing that might settle the dispute is Ancient DNA: DNA sequences from fossils found in Australia and New Guinea will provide us with a wealth of information about ancient lineages and the time when they arrived on the continent. Unfortunately, we have almost no such genetic sequences. DNA breaks down quickly, especially in warm regions – and the areas of interest to us, between Sunda and the Sahel, are in the tropics where conditions prevail that further accelerate the breakdown of ancient DNA remains.
Still, researchers are not giving up hope. “It could happen,” wrote Martin Richards, the senior author of the paper, On The Conversation website“Extracting ancient DNA in tropical regions is challenging, but in the rapidly evolving world of genetic archaeology, almost anything seems possible.”
More of the topic in Hayadan:
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