A discovery on the Indonesian island of Sulawesi has pushed back the timeline of early human sea crossings and deepened the mystery of who made them.
Archaeologists have unearthed stone tools at a site in southern Sulawesi called Calio that are at least 1.04 million years old, and possibly as ancient as 1.48 million years. Because Sulawesi has always been surrounded by deep, fast-moving waters, whoever made them would have needed to travel across open ocean.
“This is by far the earliest known evidence for the presence of early humans (hominins) on Sulawesi,” Prof Adam Brumm of Griffith University’s Australian Research Centre for Human Evolution, who co-led the study, told BBC Science Focus.
“It is now clear there is a pattern of early hominins somehow managing to cross the Wallace Line and giving rise to isolated populations on remote islands.”
The Wallace Line is a major biogeographical boundary between the Asian mainland and the islands of Wallacea. “For a non-flying land mammal, crossing from the edge of mainland Asia to the nearest islands in Wallacea, such as Sulawesi, was all but impossible because it was too far to swim and the ocean currents were too rapid,” Brumm said.
Previous discoveries showed that hominins reached the nearby island of Flores by 1.02 million years ago and Luzon in the Philippines by 700,000 years ago, with both islands later home to small-bodied species such as Homo floresiensis (nicknamed ‘the hobbit’ on account of its size) and Homo luzonensis.
On Sulawesi, however, no fossils have been found, leaving the tool-makers’ identity a mystery.
“We think it was the early Asian hominin species Homo erectus,” Brumm said. “We don't think they were using boats to do this; probably they were being washed out to sea clinging to logs or naturally formed vegetation 'rafts', perhaps during tsunamis, and thus the colonisation of Wallacean islands took place entirely by accident.”
If Homo erectus did make it to Sulawesi over a million years ago, they might have followed their own evolutionary path, perhaps becoming just as weird and wonderful as other island-dwelling hominins.
“On Flores and Luzon, fossil discoveries show that the hominins on these islands evolved in isolation into strange new species that were small in size and extremely distinctive,” Brumm said. “We have not yet found any hominin fossils on Sulawesi, so we don't know if a similar phenomenon happened on that island, but it's certainly a possibility.”
The next step for Brumm and the team? “Keep digging,” he said. “Hominin fossils are extremely rare, but millions of individual hominins would have lived and died on this island over the past million years or so, so chances are there are at least some fossil remains of the tool-makers preserved somewhere.
“We hope that with persistence (and a bit of luck) we will find the fossil, or fossils, eventually. It will, of course, be an extremely exciting discovery – perhaps even a game-changer.”
The research appears in Nature.
Read more:
- The 50,000 year old mystery of stone tools: Were they made by monkeys?
- Sunscreen might have helped early humans outlive Neanderthals
- This 7,000-year-old mummy DNA has revealed a ‘ghost’ branch of humanity
About our expert
Adam Brumm is a professor of archaeology at Griffith University. His contributions to the field span 21 years of grant-funded research in Indonesia. The papers he has published, many of them in Nature, bridge the STEM and HASS divide and cover a range of topics, from new hominin fossil discoveries in ‘Wallacea’ (the island region between Asia and Australia) to the story of human-animal relations in our recent past.