Ancient plant remains reveal humanity’s epic journey to Australia

Tiny pieces of plant resin indicate that humans lived on an island in eastern Indonesia at least 55,000 years ago, and shed light on the route modern humans may have taken to migrate to Australia.

We know that modern humans arrived in Australia by traveling southeast from mainland Asia, passing through what is now Indonesia and many of the islands of Southeast Asia. The exact date is disputed, says Dylan Gaffney of the University of Oxford. Modern genetic evidence suggests humans arrived in Australia less than 50,000 years ago, but archaeological evidence suggests they arrived earlier, “possibly 65,000 or even 80,000 years ago,” he says.

Additionally, the exact route they took is still debated, as the terrain in the region was different at the time. The Earth was in a cold glacial period, when more water was locked in ice sheets and sea levels were lower, so some of the landmasses that are now islands were connected to the mainland. In the western part of the region, Borneo, Sumatra, and Java were all part of the Asian mainland, while in the eastern part, New Guinea was connected to Australia.

So there are two possible routes that humans could have taken to reach Australia: the northern route goes straight east from Borneo to Sulawesi and then south through New Guinea to Australia, and the southern route goes through Java and then Bali and Timor to northern Australia.

To understand how people made the journey, Gaffney and his colleagues excavated Moloro Cave on Waigeo island, one of the Raja Ampat archipelago groups along the northern route, just west of New Guinea. In the sediments at the bottom of the cave, the team found evidence of human occupation, including charcoal and a few stone fragments.

Importantly, Gaffney’s team found a piece of resin just 1.4 centimeters in diameter that was angular and likely cut from a tree rather than a natural deposit, and which radiocarbon dated to be at least 55,000 years old.

The resin was probably used as fuel for fire, Gaffney says. “It’s highly flammable, so it makes a good light source in the cave,” but there are other possibilities, like fragrance or glue. Whatever its use, it indicates that humans were present on Waigeo at least 55,000 years ago. “We have evidence that people were using the northern route,” Gaffney says.

The discovery strengthens the case for the northern route by which people first reached Australia, says Kasi Norman of Griffith University in Queensland, Australia. Geographic models have always favored the northern route because it’s easier to cross the ocean. “The northern route involves more ocean crossings between islands, but shorter distances,” Norman says. Plus, “there’s always another island in sight.”

But most archaeological excavations have focused on the southern route, Norman said, and researchers like Gaffney have only recently begun to explore the northern route.

One key discovery announced in July was a 50,000-year-old cave painting of a pig found along the northern route in Sulawesi. Similarly, a study published in May found no evidence of human presence on Timor Island before 44,000 years ago, which lies on the southern route, suggesting the path was used later.

The final intriguing mystery in all of this is the absence of Denisovans (an extinct group of humans known to have lived on the Asian mainland) in the Australian fossil record. Many populations in Southeast Asia have Denisovan DNA. This includes people in Papua New Guinea who have DNA from two different Denisovan groups. This suggested, but didn’t prove, that Denisovans lived in New Guinea. But there is no trace of Denisovans in Australia. “As far as we know,” Norman says, “(But) Homo sapiens) here.”