Modern humans may have deliberately crossed the sea 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 a study published Scientific Reports.
Humans are thought to have migrated across the sea to the Ryukyu Islands from eastern Taiwan, during the Palaeolithic period (35,000-30,000 years ago). However, it has been unclear whether this sea crossing occurred by accidental drift with the Kuroshio Current, which flows from Luzon, Philippines past Taiwan and Japan, or deliberate boat voyages.
To determine the likelihood of humans reaching the Ryukyu Islands via accidental drift with the Kuroshio Current, Yousuke 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 kilometres 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 Ryukyu Islands 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 Kuroshio 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.
As the closest of the Ryukyu Islands to eastern Taiwan, Yonaguni Island, is only occasionally visible from Taiwan's coastal mountains, humans may have navigated towards islands that were only visible during the latter part of their journey, according to the authors.
Palaeolithic voyage for invisible islands beyond the horizon
University of Tokyo, Tokyo, Japan
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