New excavations of a cave site in western Sumatra called Lida Ajer indicate modern humans reached Southeast Asia between 73,000 to 63,000 years ago — up to 20,000 years earlier than archaeologists previously thought. The findings, published in the journal Nature, also suggest humans could have potentially made the crossing to Australia even earlier than the accepted 60,000 to 65,000 years ago.
Lida Ajer was originally excavated by Eugene Dubois, a Dutch paleoanthropologist 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.
Dr. Kira Westaway of Macquarie University and colleagues re-discovered the site over two decades 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 study stood on the shoulders of brilliant Dutch paleoanthropologist Eugene Dubois, famed for his discovery of ‘Java Man’,” said co-author Dr. Gilbert Price, from the University of Queensland.
“He visited a series of caves in Sumatra in the late 1800s, and in one in particular, recovered some human teeth, which is quite interesting in itself, but no one had spent much time trying to determine their significance.”
“The hardest part was trying to find the site again,” Dr. Westaway said.
“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 human teeth from Lida Ajer were identified as modern human 70 years ago by Hooijer, a Dutch paleontologist studying orangutan fossils, and while the study was convincing it lacked comparative studies of contemporaneous human fossils.
The teeth were reanalyzed 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.
“As a result of thorough documentation of the cave, reanalysis of the specimens, and a new dating program, it was confirmed the teeth were Homo sapiens, but dated to as old as 73,000 years ago,” Dr. Price said.
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 63,000 to 73,000 years ago.
“This cave has been shrouded in doubt since it was first excavated,” Dr. Westaway said.
“The modern human presence in Sumatra between 73,000-63,000 years ago occurred when the region was dominated by a closed canopy rainforest ecosystem similar to that found there today,” the researchers said.
“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 60,000 years ago.”
“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,” Dr. Westaway said.
“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.”