Re-examination of two teeth found in a Sumatran cave in the 1880s has filled a major gap in our picture of human migrations, revealing that modern humans were living in Indonesia sometime between 63,000 and 73,000 years ago.
Just a few weeks ago, evidence placed humans in northern Australia 65,000 years ago. Even before that, evidence of the presence of modern humans in Australia predated anything found in South East Asia. Yet to have got there from Africa, we must have come through Indonesia. (Unlike trapdoor spiders, humans didn't raft across the Indian Ocean).
In Nature, scientists from Indonesia, Australia, and Europe combine to show that two teeth found at Lida Ajer, eastern Sumatra, came from modern humans, and were found in a layer of sediment 63,000-73,000 years old. Although the teeth were dug up more than a century ago, the nature of the cave floor gave the modern team confidence in identifying their original resting place.
Lida Ajer Cave was first excavated by Eugene Dubois, the anthropologist who discovered “Java Man”, a find that demonstrated the spread of Homo erectus beyond Africa. Dubois located two teeth he thought might have belonged to humans, but science at the time was unable to confirm their species. He also left sketches of the cave itself and a map of how to find it, but according to Dr Kira Westaway of Macquarie University, Sydney, the map was sufficiently vague that modern scientists have struggled to follow it. Westaway told IFLScience that locals all have different ideas as to which of the many caves in the area is Lida Ajer.
In the meantime, techniques for identifying the species from which the teeth came advanced. Seventy years ago, the possibility the teeth were from orangutans was ruled out, but while research at the time pointed to them being from modern humans, rather than Homo erectus or Neanderthals, anthropologists were not sufficiently convinced to consider the implications.
When Westaway attempted to find Lida Ajer again to examine the teeth’s original location, locals tried to guide her to a cave she realized was at too high an altitude. When she protested, they suggested another half way down the mountain. “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,” she said in a statement.
Better still, Westaway found that only one section of the cave has sediment, ensuring there was no confusion where Dubois had dug. This area had been covered by flowstones, the flat equivalent of stalactites or stalagmites. The teeth have to be older than the thin layer of flowstones above them, and Westaway said they "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.”
Re-examination of the teeth using micro-CT scanning to measure the thickness of the enamel, and close investigation of the junction of the enamel and dentine, left researchers confident these really were the long sought evidence of modern humans in the region. Our ancestors’ presence in the area at this time fits with not only the settlement of Australia, but the interactions with Neanderthals and Denisovans we see in our genetic records.
Other fossils in the same layer make clear that the region was then a closed canopy rainforest. This is surprising, since it is thought our ancestors could not find sufficient food in such an environment until the development of advanced hunting techniques, thought to have emerged well after humans left Africa. “However, here we have humans making use of such challenging environments as soon as they arrived in Sumatra,” said co-author Dr Julien Louys of the Australian National University.
Westaway also pointed out to IFLScience that during the Ice Age, Lida Ajer would have been a very long way from the sea, contradicting the theory that the first migrations out of Africa clung closely to the coast.