Prehistoric axes and beads found in caves on a remote Indonesian island suggest it was a crucial staging post for sailors who lived there as the last ice age drew to a close.
Our findings, published today in PLOS ONEsuggest that humans arrived on the tropical island of Obi at least 18,000 years ago, managing to live there for at least the next 10,000 years.
It also provides the first direct archaeological evidence to support the idea that these islands were crucial to the island-hopping migration of humans through this region millennia ago.
In early April 2019, we and our Indonesian colleagues became the first archaeologists to explore Obi, in the Indonesian province of Maluku Utara.
We found eastern Indonesia’s oldest example of sharp axes, made by grinding a piece of stone into a sharp blade against a rough material such as sandstone. These were probably used to clear the forest and make canoes.
Our findings suggest that the prehistoric peoples who lived on Obi were adept at land and sea, hunting in the dense rainforest, foraging by the seashore and possibly even making canoes to travel between islands.
Our research is part of a project to learn more about how people first dispersed from mainland Asia, through the Indonesian archipelago and into Sahul, the prehistoric continent that once connected the Australia and New Guinea.
An island springboard
Recent models from CABAH researchers have identified the collection of small islands in northeast Indonesia – and Obi in particular – as the most likely “stepping stones” used by humans on their very first voyage to the is north of Sahul (modern New Guinea), approximately 65,000 to 50,000 years ago.
Migrating through this region, which bears the name Wallacea in honor of explorer and naturalist Alfred Russel Wallace, would have required multiple sea crossings. This enormous archipelago therefore has a unique significance in the history of mankind, as the region where people first undertook long, deliberate sea voyages.
Our previous research suggested that the northern Wallace Islands, including Obi, would have offered the easiest migration route. But to support this theory, we need archaeological evidence for humans living in this remote area in the ancient past. So we traveled to Obi to search for cave sites that might reveal evidence of early occupation.
tools and treasure
We found two rock shelter sites, just inland from the village of Kelo on the north coast of Obi, which were suitable for excavation. With the permission and help of the local people of Kelo, we dug a small test excavation in each shelter.
We found many artifacts, including fragments of edge-to-ground axes, some dating back around 14,000 years. The first ground axes in Kelo were made using clam shells. Axes made from shells have also been found elsewhere in this region around the same time, including on the neighboring island of Gebe to the northeast. Traditionally, they were used by the inhabitants of the region for the construction of canoes. It is highly likely that Obi axes were also used to make canoes, allowing these early peoples to maintain links between communities on neighboring islands.
The oldest cultural layers from the Kelo 6 site, containing a combination of shells and shards of stone tools, have provided us with the earliest record of human occupation on Obi, dating to around 18,000 years ago. At that time, the climate was drier and colder than today, and the island’s dense rainforests would likely have been much less impenetrable than they are now. The sea level was about 120 meters lower, meaning Obi was a much larger island, encompassing what is now the separate island of Bisa, as well as several other smaller islands nearby.
Around 11,700 years ago, at the end of the last ice age, the climate became noticeably warmer and wetter, undoubtedly making the Obi jungle much thicker. It is perhaps no coincidence that this is when we see the first evidence of axes made of stone rather than shells, possibly in response to their increased and extensive use for forest clearing and modification. increasingly dense tropical. While stone takes about twice as long to grind in an ax as shell, the harder material also retains its sharpness longer.
Judging from the bones we found in the Kelo Caves, locals mainly hunted Rothschild’s couscous, an opossum-like animal that still lives on Obi today. As the forest became denser, people probably used axes to clear patches of forest and facilitate hunting.
Again, this is probably no coincidence with volcanic stone axes – which would have remained sharp longer and are known to have been used for this purpose in New Guinea – first appearing in the archaeological record at around the time the climate was changing.
We also found obsidian, which must have been imported from another island as there is no known source on Obi, and particular types of shell beads in Kelo caves, similar to those found previously on the southern islands of Wallacea. This again supports the idea that Obi Islanders regularly traveled to other islands.
Move or relocate?
Our excavations suggest that people lived successfully in Kelo Caves for around 10,000 years. But then, around 8,000 years ago, both sites were abandoned.
Have the inhabitants completely left Obi or have they moved elsewhere on the island? Perhaps the jungle had grown so thick that human axes (even stone ones!) were no longer up to the dense undergrowth. Maybe people just moved to the coast and became primarily fishermen rather than hunters.
Whatever the reason, we have no evidence of any use of the Kelo shelters after this period, until about 1,000 years ago, when they were reoccupied by people who possessed pottery objects and made of metal. It seems likely, given Obi’s location in the middle of the “Spice Islands” of Maluku, that this last phase of occupation saw the Kelo shelters used by people involved in the historic spice trade.
We hope to find the answers to some of these questions when we return to Obi next year, COVID permitting, to dig coastal caves.
Homo erectus hand ax discovered in East Africa
Ceri Shipton et al. Early Ground Ax Technology in Wallacea: Early Excavations on Obi Island, PLOS ONE (2020). DOI: 10.1371/journal.pone.0236719
Provided by Australian National University
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