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Were the first humans to walk fully upright about two million years ago and were present during the Pleistocene. Much of the current knowledge about Homo erectus in Asia it comes from the island of Java in Indonesia, specifically on the banks of the Solo River, in the Ngandong oilfield.
In the 1930s, up to twelve skull caps and two tibiae began to be discovered in a bone bed where more than 25,000 bones of different animal species were originally found.
The dating of the human remains was difficult to carry out over decades, so the experts proposed as antiquity a wide range of dates spanning from 550,000 to 27,000 years ago.
Thanks to this long dating, for years it was hypothesized that Homo erectus may have lived simultaneously with populations of Homo sapiens, 50,000 years ago, and it was ruled out that modern humans could have evolved from these archaic human populations.
However, a new study, published in Nature, provides the exact age of the fossils found almost 90 years ago and refutes some of the previous theories.
“The remains date from between 117,000 and 108,000 years ago. This confirms that Ngandong is the youngest Homo erectus site known worldwide. We have put an end to a long controversy over the age of this important place in human evolution, "he declared. Russell L. Ciochon, scientist in the department of Anthropology at the University of Iowa (USA) and main author of the work.
The team was able to date what no other research group had achieved before due to the site's stratigraphy and confusion with the original location details from earlier excavations. They used uranium series with luminescence and electron spin resonance directly on the mammalian fossils discovered in the bone bed of the Solo River to determine the ultimate age.
“We then combined the results of these different methods using Bayesian modeling. The dating of the sediments with luminescence was not available in previous studies ”, Ciochon details. Estimates indicate that the fossils belong to the last known H. erectus individuals to ever exist.
How the last Homo erectus died
Dating allows researchers to provide information about the extinction of one of our direct ancestors. In fact, due to the disposition of the fossils found at the beginning of the 20th century - bodies and disarticulated remains that ended up there after being washed downstream - experts point out that upstream from Ngandong, a mass death event such as a flood can occur. But there are different theories about what caused these mass deaths, including a volcanic mudflow.
What is known is that this event coincided with changing environmental conditions as open forests were transformed into tropical rainforest. "When the area became more humid, the rainforest expanded eastward through Java, replacing the open forest environment associated with Homo erectus," explains the American researcher.
The disappearance of these humans in Java is simultaneous to the expansion of the tropical forest. The changing environment likely contributed to their extinction as they were likely unable to find the food sources they normally consumed or were more vulnerable to new predators.
The only hominins that have been able to survive in a jungle environment are modern humans, thanks "to our behavioral and technological adaptations."
The new research thus shows that H. erectus did not survive late enough to interact with modern humans in Java. Furthermore, as Ngandong is the youngest known H. erectus site, “there is no evidence that H. erectus has been found in modern humans”Says Ciochon.
However, in a study published in the journal Cell, an international group of scientists showed that Denisovans interbred with modern humans and an older species, transmitting a residual signal of about 1% archaic DNA.
“This oldest species was probably H. erectus. There is now speculation about where and when the Denisovans encountered Homo erectus and what were the results of those interactions ”, concludes the paleoanthropologist.
Yan Rizal et al. "Last appearance of Homo erectus at Ngandong, Java, 117,000–108,000 years ago”Nature December 18, 2019