The report of seven small stone flakes from a cornfield in South Sulawesi, Indonesia, pushed back the timeline of early human movement across Island South-East Asia. Excavators at the Calio site near the Walanae River recovered the artefacts only 1.4 metres below the surface and dated them to between 1.04 million and 1.48 million years ago, making them the oldest cultural traces yet found in Wallacea and several hundred thousand years older than the tools on Flores.
Project leaders Budianto Hakim of Indonesia’s National Research and Innovation Agency and Adam Brumm of Griffith University extracted the flakes from a thin bed of ancient river sand. Paleomagnetic readings on the sandstone and uranium-series electron-spin resonance tests on a fossil jaw of the giant pig Celebochoerus heekereni that lay beside the tools converged on a minimum age of 1.04 million years.
Each artefact was a sharp-edged flake struck from local chert cobbles. One piece was a Kombewa flake with secondary trimming that indicated deliberate retouch. Microscopic examination showed percussion bulbs, ripples and recurved cutting edges inconsistent with natural breakage. “There’s no other type of creature that is able to reliably fracture stones by hitting them at the right angle and the exact amount of force required to induce that stone to fracture in a specific way,” said Brumm.
Before Calio, the oldest recognised toolkit in Wallacea came from Mata Menge on Flores at 1.02 million years. The new evidence therefore shifted priority northward and implied that an unidentified hominin population crossed at least 50 kilometres of open water. “It is more likely that hominins got to Sulawesi by accident, most probably as a result of ‘rafting’ on natural vegetation mats,” said Brumm, according to Science Alert. “We don’t think, a million years ago, that early human species had the technology to make boats,” said Andy Herries of La Trobe University.
If the voyagers were Homo erectus—a species known on nearby Java from 1.6 million years ago—the find influences debates about Homo floresiensis, the so-called hobbit that lived on Flores until about 50,000 years ago. “I think we’ve got another piece of the puzzle here that does make it somewhat more likely that Sulawesi was the point of origin of these early humans on Flores,” said Brumm. “Perhaps, if archaic hominins were isolated in Sulawesi, they would not have suffered the same extreme anatomical changes that we see in the hominins of Flores,” he added.
No hominin bones accompanied the artefacts, and that gap fueled debate. “Possible? Certainly! Convincing? Certainly not!” wrote Dutch archaeologist Wil Roebroeks in an email critique. He questioned how many ambiguous stones were discarded before the final seven were selected, warning that entire assemblages must be assessed rather than individual pieces.
Even without skeletal remains, the dates altered regional prehistory. Earlier Sulawesi finds included a 194,000-year-old toolkit from Talepu and a modern human jaw at about 25,000 years old. The Calio ages showed that early hominins reached the island more than a million years earlier than previously known.
Hominin landfall on Flores, Luzon and now Sulawesi indicated repeated sea crossings during the Early and Middle Pleistocene. “That pattern is most important, because it adds to the startling fact that early Pleistocene hominins could somehow make sea crossings,” said Debbie Argue of the Australian National University. The Indonesian throughflow current, which moves from Sulawesi southward toward Flores, may have aided passive drift voyages, as geochronologist Kira Westaway noted, according to New Scientist.
Calio sits at the foot of the Sengkang Anticline Mountains near an ancient braided river that once supplied cobbles, water and game. Microscopic edge damage on the flakes matched cutting soft tissue or scraping plant fibres, and analysts found traces of repeated use.
Brumm’s team planned to widen trenches downslope and probe neighbouring terraces in search of deeper artefacts and, ideally, fossil hominins. “Finding elusive fossils on Sulawesi would be the team’s ‘dream discovery’,” said Brumm.
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