Groundbreaking new evidence suggests modern humans were present in Southeast Asia 20,000 years earlier than previously thought

11 August 2017

New dating of a cave site in western Sumatra called Lida Ajer has extended the timing of the earliest modern human presence in tropical Southeast Asia. The site contains fossils of rainforest fauna associated with two human teeth. Until now, the significance and validity of these remains had not been widely accepted.

A new suite of analyses, generating multiple dates and comparing the human teeth with other contemporaneous humans, has confirmed that anatomically modern humans were present in Sumatra much earlier than previously accepted. This research, published in Nature, has wide implications for the timing of human exit out of Africa and their first use of rainforests as a habitable environment.

The cave was originally excavated by Eugene Dubois, a Dutch palaeoanthropologist of ‘Java Man’ fame, in the late 1880s and revisited one hundred years later by Jon de Vos and Randy Skelton. Despite their claims for antiquity and the significance the site, it has often been ignored in models of human dispersal out of Africa and through Southeast Asia due to problems of dating and tooth identification. This study rediscovered the site over 20 years later, with the intention of establishing a firm chronology for the evidence and testing the modern human attribution of the teeth. The cave can now be reclassified as a key piece of evidence in the theories of modern human dispersal.

“The hardest part was trying to find the site again” said Dr Kira Westaway lead author of the study from Macquarie University, Sydney “we only had a sketch of the cave and a rough map from a copy of Dubois’s original field notebook – we stumbled across the cave almost by accident – but the minute I saw a large calcite column in the entrance I knew we had found the cave dug by Dubois over 120 years earlier.”

The Lida Ajer human teeth were identified as modern human 70 years ago by Hooijer, a Dutch palaeontologist studying orangutan fossils, and while the study was convincing it lacked comparative studies of contemporaneous human fossils. The teeth were reanalysed using state-of-the-art imaging techniques, allowing insight into enamel thicknesses and junctions between the enamel and dentine, critical for distinguishing human from other primate teeth. The analyses confirmed that the teeth are anatomically modern human, indicating that they were present on the Sumatran landscape at that time.

“Since the time of Hooijer’s original analysis, the evolutionary history of Eastern Asia has become more complex, with the increasing possibility of pre-human hominins being present in the area at this time. So it was important to confirm that these teeth were indeed modern human” said co-author Ass/Prof Matthew Skinner from the University of Kent, UK.

A barrage of dating techniques were applied to the sediment around the fossils, to overlying and underlying rock deposits in the cave and to associated mammal teeth, indicating that the deposit and fossils were laid down between 73-63 thousand years ago.

“This cave has been shrouded in doubt since it was first excavated” says Dr Kira Westaway. “We employed a range of dating techniques from different institutions to establish a robust chronology that would, after 120 years, finally put an end to the uncertainty associated with the age and significance of these teeth”

“We were lucky to have some of the best dating facilities in the world at our disposal, including the same pieces of equipment that had earlier dated the famous ‘Hobbit’ fossils of Southeast Asia” said co-author Dr Gilbert Price from the University of Queensland, Brisbane.

The modern human presence in Sumatra between 73-63 thousands years ago occurred when the region was dominated by a closed canopy rainforest ecosystem similar to that found there today. Thus, these teeth provide the earliest unambiguous evidence of occupation of rainforest conditions by anatomically modern humans. Successful exploitation of rainforest environments is difficult, and requires the capacity for complex planning and technological innovations to secure adequate resources. Our study indicates that such innovations and capacities were in place in Asia by at least 60 thousand years ago.

“Living in a rainforest was not thought to be possible until only the last few thousand years” says co-author Dr Julien Louys formerly from Australian National University, “this is because sourcing enough carbohydrates and proteins in dense canopy forests requires sophisticated hunting technology and knowledge that the first humans out of Africa would not have possessed. However, here we have humans making use of such challenging environments as soon as they arrived in Sumatra”.

Southeast Asia is a key region in the path of human dispersal from Africa round to Australia, as all hominins would have had to pass through this region en route to Australia. A change in the date of arrival in this region has huge implications for debates on when the first Australians reached our shores.“Sumatra is not on the known dispersal route through Southeast Asia so the fact that we find an early modern human presence there and so far inland is surprising” says Dr Westaway.

Other members of the research team included; the late Rokus Due, Wahyu Saptomo, Bambang Sulistyanto, (ARKENAS) the late Prof Mike Morwood, Gert van den Bergh (University of Wollongong), Jian-xin Zhao (University of Queensland), Maxime Aubert, Tanya Smith (Griffith University), Renaud Joannes-Boyau (Southern Cross University), Matthew Skinner (University of Kent), Tim Compton, Chris Stringer (Natural History Museum), Richard Bailey (University of Oxford), Jon de Vos (Naturalis Museum), Alistrair Pike (University of Southampton), Yan Rizal, J Zaim, Wayhu Santoso, a Trihascaryo (Institue of Technology, Bandung) and Les Kinsley (Australian National University).

The research was supported by Australian Research Council grants, a Leaky Foundation grant, the Human Origins Research Fund, the Calleva Foundation, and additional funds from Macquarie University and Australian National University.

The paper, entitled “An early modern human presence in Sumatra at 73-63 thousand years ago” can be obtained from Nature’s press site.

Filed under: Featured Humanities

An international team of researchers lead by Macquarie University used advanced scanning
techniques to identify and date ancient human teeth discovered in a Sumatran cave site

An international team of researchers lead by Macquarie University used advanced scanning techniques to identify and date ancient human teeth discovered in a Sumatran cave site

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