Modern Humans May Have Lived Alongside an Extinct Human Species in Ancient Indonesia

Deep down in a cave on the Indonesian island of Sulawesi, layer upon layer of archaeological evidence may show how modern humans lived alongside archaic humans. Years of excavation have brought the cave’s history to light, revealing a major transition between two phases of human occupation during the Pleistocene epoch.

A new study published in PLOS One describes the stone artifacts and fossilized animal remains that have been found 8 meters (about 26 feet) below the surface at the limestone cave, known as Leang Bulu Bettue. The findings establish a clear divide between two phases of human occupation; the later phase, marked by improved toolkits and artistic expression, may have been ushered in by the arrival of modern humans as early as 65,000 years ago.

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Turning Back Time

The island of Sulawesi is home to several archaeological sites that have been crucial in studies of hominin expansion into Southeast Asia. Previous research has found that hominins likely began occupying the island at least 1.04 million years ago, according to a study in Nature. However, archaeologists haven’t determined which archaic hominin species started living here first; it could have been Homo erectus, Denisovans, a relative of Homo floresiensis (which inhabited the nearby island of Flores), or even a species that isn’t yet documented.

Over the years, excavations at Leang Bulu Bettue have gradually unearthed additional details about the hominin occupants of the cave. Now, archaeologists have reached depths of 8 meters, encountering layers of preserved evidence that have never been observed before. While the initial layers beneath the surface show the items left by modern humans, the lower layers contain the remnants of archaic human occupation.

“The depth and continuity of the cultural sequence at Leang Bulu Bettue now positions this cave as a flagship site for investigating whether these two human lineages overlapped in time,” said lead author Basran Burhan, a Ph.D. candidate at Griffith University, in a statement.

The oldest stone tool found at the cave dates back to between 132,300 and 208,400 years ago, before modern humans had arrived.

A New Phase of Human Occupation

The older layers at Leang Bulu Bettue reflect what the researchers are calling “Phase I” of human occupation in the cave. This phase is defined by stone artifact production using core and flake technology (which involves striking flakes off a rock), along with the butchery of large vertebrates like dwarf bovids (wild cattle that are endemic to Sulawesi) and now-extinct Asian straight-tusked elephants.

“These activities appear to represent an archaic hominin cultural tradition that persisted on Sulawesi well into the Late Pleistocene,” said author Adam Brumm, an archaeologist at Griffith University, in the press statement. “By around 40,000 years ago, however, the archaeological record shows a dramatic shift.”

The traditions of Phase I were replaced by a new cultural phase (Phase II), seen in evidence from the layers just below the surface at Leang Bulu Bettue. This later phase is characterized by a more complex technological toolkit, as well as the use of pigments, leading to the first instance of artistic expression and symbolic behavior at the cave.

“The distinct behavioral break between these phases may reflect a major demographic and cultural transition on Sulawesi, specifically the arrival of our species in the local environment and the replacement of the earlier hominid population,” said Basran.

The Arrival of Modern Humans

The researchers suggest that modern humans may have reached Sulawesi as early as 65,000 years ago, coinciding with their arrival in Australia. These modern humans may have lived alongside and interacted with the archaic humans that had already been living there for a million years. The stone tool technology of the modern human newcomers eventually replaced the archaic human technology by 40,000 years ago.

According to the researchers, there are several additional meters of archaeological layers beneath the current deepest level that have not yet been excavated. Going deeper down into the cave’s history, therefore, is likely to reveal even more evidence of Sulawesi’s ancient inhabitants.

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