Not just drifting by

Risky crossing likely a migration choice.

Whether ancient humans made sea crossings by choice or by chance is a common topic of debate among historians.

In the case of the migration of people from what is now

Taiwan to the Ryukyu Islands of southwestern Japan some 30,000 years ago, choice seems increasingly likely because new research suggests chance wasn’t.

And that’s despite the fact that the travellers initially would not have been able to see where they would eventually land, and the voyage would have taken them across the Kuroshio Current, one of the strongest in the world.

“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,” says Yosuke Kaifu from Japan’s University of Tokyo. “The destination can be seen from the top of a coastal mountain in Taiwan, but not from the coast.”

To investigate the likelihood of the journey occurring by chance, the researchers measured the effect of the Kuroshio on drifting craft.

Kaifu and his team studied the trajectories of 138 satellitetracked buoys, which drifted past Taiwan or northeast Luzon in the Philippines between 1989 and 2017.

Of the 122 that passed Taiwan, 114 were carried northward by the Kuroshio; the only three that came anywhere near the Ryukyu Islands did so under adverse weather conditions.

As geological records suggest the flow of the Kuroshio has remained unchanged for the past 100,000 years, the study indicates that people in drifting boats were highly unlikely to reach the islands by accident.

“The results were clearer than I would have expected,” says Kaifu. “If they crossed this sea deliberately, it must have been a bold act of exploration.”