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Ancient Ocean Migration Was Choice, Not Chance: Study

Scientists have conclusively settled a long-lived debate, finding in a study released Thursday that Paleolithic people migrating from ancient Taiwan to the Ryukyu Islands of southwestern Japan did so intentionally, not by coincidence.

(CN) — Scientists have conclusively settled a long-lived debate, finding in a study released Thursday that Paleolithic people migrating from ancient Taiwan to the Ryukyu Islands of southwestern Japan did so intentionally, not by coincidence.

The study, published in the journal Scientific Reports, was headed by Professor Yosuke Kaifu from the University Museum at the University of Tokyo and his colleagues as they discuss how they replicated the journey to the island chain with advanced technology and a lot of buoys.

For years, researchers have struggled to agree on why they believe early humans would have migrated across open waters to settle on new lands. Although it is generally accepted that migration is typically driven by availability of resources, climate patterns or changes, surrounding conflicts and other environmental factors, it is unclear how these people got to where they landed. 

The colonization of the Ryukyu Islands, including Okinawa, is an instance of particular intrigue. The Paleolithic people who made the journey would have done so approximately 35,000-30,000 years ago — a daunting feat for a group of hunter-gatherers. 

These island-bound settlers would have needed aggressive preparation to accomplish this and successfully live there, casting doubt for the authors on the possibility that this may have been a coincidental migration.

"There have been many studies on Paleolithic migrations to Australia and its neighboring landmasses, often discussing whether these journeys were accidental or intentional," Kaifu said. "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,” she added.

Previous studies of this archipelago show that early settlers had travelled in groups with their families, and were able to adapt to the subtropical forest climate. 

Well preserved human fossils have been discovered here, as well as impressive artifacts, and evidence has been found that two distinct cultures existed on the north and south sides of the islands. The question still stands as to whether this was an intentional discovery or not.

To test their hypothesis, the team developed a fleet of 138 buoys able to be tracked via satellite. They then set them adrift to replicate what the migration trail might have looked like, and if it could be achieved again by chance. Out of all of the buoys released, very few even came close to the islands, making it more than likely that the drifters set sail with purpose.

"The results were clearer than I would have expected," Kaifu said. "Only four of the buoys came within 20 kilometers 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," she added.

Tracking data for 138 buoys, including several which ventured relatively near the target islands. (Credit: Tien-Hsia Kuo)

The authors point out that one possible fault in the study could be an unaccounted-for change in the ocean’s tides from then up until now. But they note that all evidence shows that the region’s currents have remained steady and stable for the past 100,000 years. 

They also have reason to believe that the travelers would have seen relatively normal conditions during their trip, as unstable or stormy conditions could have thrown them off course or endangered their families onboard.

"At the beginning, I had no idea how to demonstrate the intentionality of the sea crossings, but I was lucky enough to meet my co-authors in Taiwan, leading authorities of the Kuroshio, and came across the idea of using the tracking buoys," Kaifu said. 

"Now, our results suggest the drift hypothesis for Paleolithic migration in this region is almost impossible. I believe we succeeded in making a strong argument that the ancient populations in question were not passengers of chance, but explorers," she concluded.

A previous study conducted by Kaifu consisted of a team rowing a dugout canoe, similar to what ancient humans would have used, across more than 120 miles of sea to test the probability of the voyage’s success. The trip took about 45 hours to complete, including time to rest, but the explorers said they could see it as a very plausible way the early humans could have succeeded in transporting themselves and their families to the Ryukyu Islands.

One of the satellite-tracking buoys. (Credit: Lagrangian Drifter Laboratory/University of California, San Diego)
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