More than a million years ago, the first human relatives crossed the vast sea to reach the Indonesian island of Sulawesi. The discovery breaks the record for human migration in Southeast Asia and contradicts what scientists thought early humans could have accomplished.
Clues in ancient stone
The tale began in a peaceful cornfield in South Sulawesi, where archaeologists from Indonesia and Australia discovered seven small but amazing stone tools. Tools found in layers of sandstone at a place called Calio told an even older story than anyone had imagined.
Using techniques such as paleomagnetism and uranium series dating, the researchers determined that the artifacts were at least 1.04 million years old, if as old as 1.48 million. Their findings, published in Nature, extend the history of human presence in the area by hundreds of thousands of years.
The location of Sulawesi in the Wallacean archipelago (Wallacea) is a zone of oceanic islands between the continental regions of Asia and Australia (Sunda and Sahul, respectively). (CREDIT: Nature)
Each flake showed carefully shaped and cut edges, signs that they had been used as scraping or cutting tools. One has been retouched with care, indicating skill and training rather than careless rock-breaking.
A journey through deep water
Sulawesi lies to the east of the Sunda continental shelf, separated from the Asian mainland by deep seas that never completely dried up even during the ice ages. This interior of Wallacea is a border, drawn by a line called the Wallace Line, previously thought to have been successfully crossed only by Homo sapiens in the last 100,000 years.
Cali tools turn this on its side. Whoever designed them must have traveled miles on the high seas hundreds of thousands of years before man existed. How they managed it, no one knows.
Brumm says this could have been accidental – perhaps small groups were swept out to sea by rafts of vegetation after storms or tsunamis. “We’re not talking about scheduled trips,” he said. “But these transitions show remarkable resilience and adaptability.”
A site of floating layers of pebbly sandstone with fossils and stone artefacts exposed at the ground surface in an agricultural field. Archaeological excavations in Cali (2022). (CREDIT: Nature)
Who were these early travelers?
Human remains have not been excavated, so the makers of the tools are unknown. Scientists believe it could have been Homo erectus, known from Java around 1.6 million years ago. years. Others suggest relatives of Homo floresiensis, a group of “hobbits” on the nearby island of Flores, or Homo luzonensis of the Philippines.
If they had arrived in Sulawesi more than a million years ago, they might have evolved separately and even developed different traits or even become a different species.
A wider network of ancient pioneers
The discovery of Sulawesi fits the pattern of island expansion in Southeast Asia. The tools at Flores are approximately 1.02 million years old, while evidence of tool use and animal butchery from Luzon dates to between 777,000 and 631,000 years ago.
Later, Flores was occupied by Homo floresiensis and Luzon by Homo luzonensis. These findings suggest multiple waves of migration into the region over a long period of time, not just one.
A fragment of a fossil maxilla of Celebochoerus heekereni from Cali. The specimen was embedded in coarse sandstone and sampled in two separate anchorage blocks found at the same site. (CREDIT: Nature)
The potash evidence is now some of the earliest evidence of human occupation east of the Wallace Line, suggesting that early humans were far more resourceful and capable than previously thought.
Rethinking human migration
This discovery turns scientists’ knowledge of early human migration upside down. For a long time, migration was thought to occur only over land. Tools from Sulawesi show that even early humans could swim across deep oceans, something previously thought they couldn’t do.
“This discovery turns the chronology of human ingenuity on its head,” Brumm said. “These were pioneers, innovative and clever, crossing some of the most remote parts of the world.
Hakim and Brumm plan to continue exploring the rugged interior of Sulawesi, searching for fossils that could reveal who these toolmakers were. They believe the island’s limestone caves and valleys may still hold crucial clues.
The deepest stone artifact excavated at Cali (artifact 6) was found 56 cm below the ground surface in layer 3b. (CREDIT: Nature)
Why is this important?
This discovery doesn’t just repeat human history, it changes our understanding of intelligence, survival, and exploration. This reveals that early humans swam across open water long before Homo sapiens ever did, showing that they had extraordinary flexibility and problem-solving abilities.
Looking back at how the first visitors to the islands survived provides an insight into how human culture and innovation evolved. Future excavations may even reveal a new branch of the human family tree.
Sulawesi may hold the key to how early humans populated Asia and how isolation made us who we are today.
The research results are available online in the journal Nature.
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