Scientists Compare Stone Age Navigation Techniques with One of the Planet's Strongest Currents

Archaeologists estimate that humans first arrived on the Ryukyu Islands off the southwestern coast of Japan sometime between 35,000 and 27,500 years ago. How they did so, however, remains a mystery, especially since they would have had to cross one of the planet’s strongest ocean currents. To address this enduring question, scientists decided to attempt the Paleolithic voyage themselves.

Using replicas of tools that existed in the Japanese Archipelago during the Upper Paleolithic (around 50,000 to 10,000 years ago), researchers in Japan built a dugout canoe and used it to traverse the 68.4-mile-wide (110-kilometer) strait between Taiwan and Yonaguni Island, including the powerful Kuroshio current, in around 45 hours. The successful voyage represents a possible way people in present-day Taiwan may have traveled to the islands tens of thousands of years ago.

“Our 7.5-meter-long dugout, manufactured with edge-ground stone axes, was speedy and durable enough to cross this strait,” the researchers wrote in the study, published today in Science Advances. “This supports the early development of functional boats, such as dugouts, while our experiment also highlighted that this type of sea travel was possible only for experienced paddlers with advanced navigational skills.”

One of the greatest challenges to studying prehistoric seafaring is the fact that such ancient water vessels made of organic material, such as wood, have long since disintegrated. Without direct archaeological evidence, the next best way to shed light on how ancient people did things is through experimental archaeology—identifying possible approaches to bygone endeavors by physically replicating them in a simulated historical context.

University of Tokyo anthropologist Yousuke Kaifu and his co-authors have been attempting to reach the Ryukyu Islands à-la Paleolithic—without modern navigation technologies like GPS or compasses—since 2013. Before their successful voyage in 2019, they had experimented with reed-bundle rafts and bamboo rafts, neither of which were successful in crossing the Kuroshio Current. The winning design was a canoe made from a hollowed-out and polished Japanese cedar tree with a fire-charred interior, which carried five crew members.

“Given the absence of archaeological remains of Pleistocene watercraft, we narrowed down the possible Paleolithic seagoing craft by referencing the Holocene archeological and ethnographic records and considering the material availability, technological limitations of the time, and the voyaging capabilities of each craft,” the researchers explained. The Holocene, which began some 11,700 years ago, is the current time period. “We also aimed to investigate travel time, amount of efforts required, and other realities of Paleolithic ocean crossing for the first South Ryukyu islanders.”

In this spirit, the team developed computer models to simulate what such a crossing may have been like with Late Pleistocene oceanic conditions. According to the simulations—which also integrated data collected during the experimental voyage—the prehistoric journey’s success would have been determined by the starting point (ideally, calm bays), directional strategy (first paddle east-southeast, then northeast), and navigational skills (using the stars and Sun).

Furthermore, “our separate numerical simulation study suggests that this type of boat could also travel to Yonaguni Island from a different northern departure point in Taiwan (Taroko) across both the modern and Late Pleistocene oceans,” they added. “Paleolithic people are often regarded as ‘inferior’ among the general public, primarily due to their ‘primitive’ culture and technology. In sharp contrast, our [work] highlighted that they accomplished something extraordinary with the rudimentary technology available to them at the time.”

While such experimental projects can’t replace direct archaeological evidence, the study joins a host of recent hands-on approaches offering creative theories in the absence of direct material evidence.