Paleolithic people deliberately crossed the challenging ocean to migrate to the Ryukyu Islands of southwestern Japan, even though the islands would not have been visible on the horizon when they set out, according to new research by scientists from the University Museum at the University of Tokyo, the National Taiwan University’s Institute of Oceanography and Japan’s National Museum of Nature and Science. The team’s analysis of satellite-tracked buoys drifting in the ocean demonstrated that accidental drift does not explain maritime migration to the Ryukyus, where the local ocean flows have kept the same since the Late Pleistocene.
An ancient Japanese wooden sailing vessel. Image credit: Pratyeka / CC BY-SA 4.0.
Migration to the Ryukyu Islands is difficult because it requires navigation across one of the world’s strongest current, the Kuroshio.
“There have been many studies on Paleolithic migrations to Australia and its neighboring landmasses, often discussing whether these journeys were accidental or intentional,” said University of Tokyo’s Professor Yousuke Kaifu.
“Our study looks specifically at the migration to the Ryukyu Islands, because it is not just historically significant, but is also very difficult to get there.”
“The destination can be seen from the top of a coastal mountain in Taiwan, but not from the coast.”
“In addition, it is on the opposite side of the Kuroshio, one of the strongest currents in the world. If they crossed this sea deliberately, it must have been a bold act of exploration.”
To determine the likelihood of humans reaching the 1,200 km-long chain of islands via accidental drift with the Kuroshio Current, Professor Kaifu and colleagues studied the trajectories of 138 satellite-tracked buoys, which drifted past Taiwan or northeastern Luzon between 1989 and 2017.
Of the 122 buoys that drifted past Taiwan 114 were carried northward by the Kuroshio and, of these, 3 came within 20 km of the central and south Ryukyu Islands under adverse weather conditions.
Of the 16 buoys that drifted past Luzon, 13 drifted with the Kuroshio but only one moved towards the Ryukyus due to a typhoon.
As the flow of the Kuroshio Current is thought to have remained unchanged during the past 100,000 years, the results indicate that humans in drifting boats were unlikely to reach the islands via accidental drift with the current.
The findings suggest that humans deliberately crossed one of the world’s strongest currents in order to migrate to the Ryukyu Islands approximately 35,000 years ago.
“The results were clearer than I would have expected,” Professor Kaifu said.
“Only four of the buoys came within 20 km of any of the Ryukyu Islands, and all of these were due to adverse weather conditions.”
“If you were an ancient mariner, it’s very unlikely you would have set out on any kind of journey with such a storm on the horizon.”
“What this tells us is that the Kuroshio directs drifters away from, rather than towards, the Ryukyu Islands; in other words, that region must have been actively navigated.”
The findings were published in the journal Scientific Reports.
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Y. Kaifu et al. 2020. Palaeolithic voyage for invisible islands beyond the horizon. Sci Rep 10, 19785; doi: 10.1038/s41598-020-76831-7
