Polynesian navigation snow. In the mid-20th century, Thor Heyerdahl proposed a new theory of Polynesian origins (one which did not win general acceptance), arguing that the Polynesians had migrated from South America on balsa-log boats. The presence in the Cook Islands of sweet potato that is a plant native to the Americas (called "kūmara" in Māori), which have been radiocarbon-dated to 1000 CE, has been cited as evidence that Americans could have traveled to Oceania. The current thinking is that sweet potato was brought to central Polynesia circa 700 CE and spread across Polynesia from there, possibly by Polynesians who had traveled
Thor Heyerdahl history, consulting what was then the world's largest private collection of books and papers on Polynesia, owned by Bjarne Kroepelien, a wealthy wine merchant in Oslo. (This collection was later purchased by the University of Oslo Library from Kroepelien's heirs and was attached to the Kon-Tiki Museum research department.) After seven terms and consultations with experts in Berlin, a project was developed and sponsored by Heyerdahl's zoology professors, Kristine Bonnevie and Hjalmar Broch. He was to visit some isolated Pacific island groups and study how the local animals had found their way there. Just before sailing together to the Marquesas