Scientists Retrace 30,000-Year-Old Sea Voyage, in a Hollowed-Out Log

In 1947, against the best navigational advice, the Norwegian explorer Thor Heyerdahl and five crew members set sail from Peru on a balsa wood raft to test his theory that ancient South American cultures could have reached Polynesia. The frail vessel, called Kon-Tiki, crossed several thousand nautical miles of the Pacific in 103 days and showed that his anthropological hunch was at least feasible.

In 2019, in much the same spirit, a research team led by Yousuke Kaifu, an anthropologist at the University of Tokyo, built a dugout canoe in order to study another aspect of western Pacific migration: How did ancient humans, more than 30,000 years ago, navigate the powerful Kuroshio current from Taiwan to southern Japanese islands, such as Okinawa, without maps, metal tools or modern boats? “Since any physical evidence would have been washed away by the sea, we turned to experimental archaeology, in a similar vein to the Kon-Tiki,” Dr. Kaifu said.

Two new studies published on Wednesday in the academic journal Science Advances presented the results of those experiments. In one report, advanced ocean models recreated hundreds of virtual voyages to pinpoint the most plausible routes for the crossing. Dr. said, "We tested various paddling methods, starting points, and seasons under both modern and prehistoric conditions." Kaifu said.

The additional paper details the 45-hour journey that Dr. Kaifu’s crew made from eastern Taiwan to Yonaguni Island in the southern Ryukyus. The mariners, four men and one woman, paddled the 25-foot canoe, a hollowed-out cedar log christened Sugime, for 122 nautical miles on the open sea, relying solely on the stars, sun and wind for their bearings. Often, they could not see their target island.

“Yosuke Kaifu’s team has found the most likely answer to the migration question,” said Peter Bellwood, an archaeologist at the Australian National University who was not involved in the undertaking. Such a crossing between islands, he said, would have been one of the oldest, and among the longest, in the history of Homo sapiens up to that period, exceeded only by the migration to Australia from eastern Indonesia some 50,000 years ago.

From mainland Asia to the Japanese archipelago, early humans most likely traveled by land bridges and watercraft. Korea to Kyushu, Russia to Hokkaido, and Taiwan to Okinawa were the three main options. Relics from six islands within the 750-mile Ryukyu chain indicate that people migrated there between 35,000 and 30,000 years ago, arriving from both the north, via Kyushu, and the south, via Taiwan.

Even during the last ice age with its low sea levels, "the islands were always located at least 50 miles from the East Asian coastline, and up to 110 miles apart from each other," Dr. Bellwood said. Geologic records suggest that the Kuroshio, also known as the Black Stream, has remained stable for 100,000 years or more.

Dr. In 2013, Kaifu came up with the idea for the migration project, but she didn't have enough money to make it happen. Three years later, he persuaded Japan’s National Museum of Science and Nature, where he worked as a researcher, to act as a sponsor. Financed largely by crowdfunding and counseled by sea kayakers, his team attempted the 40-nautical-mile route from the Yonaguni to the Iriomote islands in boats made from cattail reeds. The attempt was a failure. Despite being stable, the vessels were too slow to deal with the strong currents. The researchers experimented with rafts made of bamboo and rattan in 2017 with the assistance of Taiwan's National Museum of Prehistory. Similar to the reed crafts, a prototype was durable but not fast enough to negotiate the Kuroshio. A second, lighter version was prone to cracking and did not last long in the high seas.

After calculating that crossing the Kuroshio would require a speed of at least two nautical miles per hour, Dr. Kaifu searched for heavier materials. A large Japanese cedar was felled and carved using stone axes modeled after tools from about 28,000 B.C. “The idea was to replicate the canoe-building methods that prehistoric seafarers may have used,” Dr. Kaifu stated The Sugime set off from Taiwan six summers ago. This time, the voyage was a success.

Dr. Kaifu does not believe a return journey would have been possible. “If you have a map and know the flow pattern of the Kuroshio, you can plan your return,” he said. “But such things probably did not take place until much later in history.”

Did the ancient mariners arrive at the Ryukus by accident or did they carefully plan their route? Dr. Kaifu noted that the islands could be spied from the top of one of Taiwan’s coastal mountains, indicating intentional travel. To test this, his team set 138 satellite-tracked buoys adrift and found that only four came within 12 miles of any of the islands, and those had been driven by storms.

"That tells us that the Kuroshio steers drifters away from the Ryukyu Islands rather than toward them," Dr. Kaifu said. “It also tells us that those male and female pioneers must have been experienced paddlers with effective strategies and a strong will to brave the unknown.”

In his view, the Japanese islanders of antiquity were not mere passengers of chance, but die-hard explorers.

A correction was made on June 27, 2025: An earlier version of this article misidentified the journal in which two new studies were published. It is Science Advances, not Science.