Unlocking a 30,000-year-old mystery, scientists now believe they know how early humans successfully navigated the seas to migrate to Japanese islands. 

In 2019, a team of researchers in Japan demonstrated in an experiment that a crew of five in a dugout canoe could sail from Taiwan through one of the world’s strongest currents to reach Yonagunijima island, Japan’s westernmost island.

In an update to the experiment, the team identified the route and timing that would have made such a voyage possible.

The researchers reported that the crossing highly likely occurred during the Paleolithic Age if the starting point and direction of travel were altered based on simulations incorporating modern and prehistoric oceanic circulation patterns.

Yousuke Kaifu, leader of the research project, said he believed that ancient humans living on the east coast of Taiwan were aware from fishing at sea of the powerful Kuroshio Current, which flows south to north between the two islands.

In addition, these early seafarers knew that they would be swept away by the current if they ventured out too far.

“Among early humans were a group of experienced paddlers who were adept at rowing a dugout canoe,” said Kaifu, professor of human evolution and migration at the University of Tokyo’s University Museum. “They must have tackled the seafaring challenge with a strategy for handling the current, knowing that it is there and how it flows.”

The study by Kaifu and other scientists from Ehime University, the Japan Agency for Marine-Earth Science Technology and other institutions was reported in the U.S. scientific journal Science Advances on June 25. 

OVERCOMING KUROSHIO CURRENT

The ancestors of the Japanese are thought to have migrated via several routes.

One route was from Taiwan and the Philippines to the Ryukyus, a chain of islands located between the main island of Kyushu and Taiwan.

The remnants of artifacts and structures dating to 35,000 years ago have turned up in these islands.

But how prehistoric mariners could navigate the open sea against the strong Kuroshio, which is also known as the Black Stream, was a major question.

Kaifu’s project, dubbed “Holistic Reenactment Project of Voyages 30,000 Years Ago,” aimed at finding a plausible hypothesis. 

The project, organized by the National Museum of Nature and Science, Tokyo, began with building a vessel that the seafarers might have used.

The team tested reed-bundled rafts and rafts made of bamboo and rattan between 2016 and 2018, but they were found to be too slow to negotiate the Kuroshio.

In the third attempt, a non-sailing dugout canoe was built of a Japanese cedar tree with stone axes modeling after tools dating 30,000 years ago.

A crew of five--four men and one woman, including sea kayaking guides--successfully traveled to Yonagunijima on the 7.5-meter-long canoe, paddling for about 200 kilometers from Taiwan in July 2019.

In the 45-hour journey, the crew navigated through using the sun, stars and prevailing winds. 

While the 2019 crossing was successful, it was a one-off event.

And there were some points researchers needed to consider before concluding that it was still feasible for seafarers in prehistoric times to cross the seas, given the differences in ocean and climate conditions between then and now.

SCENARIO REPLICATES LONG-AGO VOYAGE

In the latest experiment, the crew departed from a location some 140 km southwest of Yonagunijima to avoid the full strength of the current, which flows at a speed of 1-2 meters per second.

But there was an issue with this selection: Yonagunijima was nowhere to be seen from the top of the mountains near the departure site, likely providing no motiviation for braving the ocean in search of new lands.

In addition, research showed that 30,000 years ago, sea levels were lower than today and the Kuroshio flowed in a different pattern in the Paleolithic Age.

Kaifu’s team studied various scenarios for virtual voyages by simulating the current based on modern and prehistoric ocean models.

In the simulation, the departure point was moved to a site more than 100 km north from the experiment to make Yonagunijima visible from nearby mountains on a fine day, the adjustment meant to make intentional seafaring likely.

As a result, the Kuroshio currents around the new starting point were estimated to flow 10-20 percent faster than in the experiment due to a change in the sea floor topography and flowed slightly eastward.

If mariners headed east straight toward Yonagunijima, they would have been pushed off course by the current and failed to spot the island, according to the study.

But the researchers also showed that they could have reached the island in 28.6 hours, about 17 hours shorter than in the experiment, if they took into consideration the Kuroshio’s flow pattern, paddling to the southeast.

Even if the mariners traveled slower than the crew did in the experiment, it was nearly certain that they could have found the targeted island, the findings also showed.

In wrapping up the project, Kaifu expressed awe for the ancient seafarers who undertook the perilous journey.

“We understand from our failed attempts that the sea crossing was a formidable undertaking for them, considering they only had primitive technology,” he said. “The dugout canoe must have been a cutting-edge product at the time, but they still needed to continue to work extremely hard to maneuver it and successfully pull off the voyage. I just find it amazing.”

A short documentary and videos of the project are available at the Holistic Reenactment Project of Voyages 30,000 Years Ago section of the website for the National Museum of Nature and Science, Tokyo, at（https://www.kahaku.go.jp/research/activities/special/koukai/ ）

PHOTOS
1 A five-member crew sets off from eastern Taiwan on July 7, 2019, in a dugout canoe to cross the open sea to reach Yonagunijima island in Japan in a project aimed to uncover how ancient mariners migrated 30,000 years ago. (Provided by Yousuke Kaifu)

2 A view of the sea toward the direction of Japan’s Yonagunijima island from Mount Liwu in Taiwan. The powerful Kuroshio Current flows offshore. (Provided by Yousuke Kaifu)

3 A stone axe with a handle was made to build a canoe used in the 2019 experimental seafaring. The axe was modeled after tools from the Paleolithic Age. (Provided by Yousuke Kaifu)

4 A Japanese cedar tree measuring 1 meter across was felled with a wooden axe to build a dugout canoe. (Provided by Yousuke Kaifu)

5 Yosuke Kaifu, left, professor of human evolution and migration at the University of Tokyo’s University Museum, Yu-Lin Chang, center, deputy senior scientist with the Japan Agency for Marine-Earth Science Technology, and Xinyu Guo, professor of marine environmental studies at Ehime University, at a news conference in Tokyo in June (Rintaro Sakurai)