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An international group of researchers comprising experts from the Natural History Museum and led by the University of Adelaide conducted a comprehensive genetic analysis and found no evidence of interbreeding between modern humans and ancient humans known from the Southeast Asian Island fossil record. The team has found further DNA evidence from our mysterious ancient cousins, the Denisovans, which could mean that there are major discoveries to come in the area.
In the study published in Nature’s ecology and evolution, researchers examined the genomes of more than 400 modern humans to study interbreeding events between ancient humans and modern human populations that arrived on the Southeast Asian island 50,000 to 60,000 ago. years.
In particular, they focused on detecting signatures that suggest crosses of deeply divergent species known from the region’s fossil record.
The region contains one of the richest fossil records (at least 1.6 million years old) documenting human evolution around the world. Currently, there are three distinct ancient humans recognized from the fossil record in the region: Man standing, Homo floresiensis (known as the Hobbits of the Island of Flores) and Homo luzonensis.
These species are known to have survived until about 50,000 to 60,000 years ago in cases of Homo floresiensis and Homo luzonensis, and about 108,000 years for Man standing, meaning they may have overlapped with the arrival of modern human populations.
The results of the study showed no evidence of interbreeding. Nonetheless, the team was able to confirm previous results showing high levels of Denisovan ancestry in the region.
Senior author and research associate at ARC University of Adelaide, Dr João Teixeira, said: “ Unlike our other cousins, the Neanderthals, who have many fossils in Europe, the Denisovans are known almost only from DNA archives. The only physical evidence of Denisovan’s existence was a finger bone and a few other fragments found in a cave in Siberia and, more recently, a piece of jawbone found on the Tibetan plateau.
“We know from our own genetic records that the Denisovans mixed with modern humans who came from Africa 50,000 to 60,000 years ago both to Asia and when modern humans crossed the island. from Southeast Asia to Australia. Denisovan DNA levels in contemporary populations indicate that significant interbreeding has occurred on the island of Southeast Asia. The mystery remains then, why haven’t we found their fossils alongside other ancient humans in the area? Do we need to re-examine the existing fossil record to consider other possibilities?
Co-author Professor Chris Stringer of the Natural History Museum added: “ While the known fossils of Man standing, Homo floresiensis and Homo luzonensis may appear to be in the right place and at the right time to represent the mysterious “Southern Denisovans”, their ancestors were probably in the island of Southeast Asia at least 700,000 years ago. This means that their lineages are too old to represent the Denisovans who, according to their DNA, were more closely related to Neanderthals and modern humans.
Co-author Professor Kris Helgen, Chief Scientist and Director of the Australian Museum Research Institute, said: “ These analyzes provide an important window into human evolution in a fascinating region and demonstrate the need for more archaeological research in the region between mainland Asia and Australia. ‘
Professor Helgen added: “This research also sheds light on a ‘megafaunal’ model of survival that coincides with known areas of premodern human occupation in this part of the world. Large animals that survive in the area today include the Komodo dragon, the Babirusa (a pig with remarkable overturned tusks), and the Tamaraw and Anoas (small wild buffaloes). This suggests that long-term exposure to the pressure of hunting by ancient humans may have facilitated the survival of the megafaunal species in subsequent contact with modern humans. Areas with no documented premodern human occurrence, such as Australia and New Guinea, have experienced the complete extinction of land animals larger than humans over the past 50,000 years.
Dr Teixeira said: “The research corroborates previous studies that the Denisovans were on an island in Southeast Asia and that modern humans did not intersect with more divergent human groups in the region. This opens up two equally exciting possibilities: either a major discovery is underway, or we need to reassess the current fossil record of the Southeast Asian island.
“Whichever way you choose to look at it, exciting times lie ahead in paleoanthropology.
The article was published in Nature Ecology and Evolution on March 22, 2021.
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