Polynesia of the plant in the Cook Islands have been radiocarbon-dated to 1000, and current thinking is that it was brought to central Polynesia c. 700 and spread across Polynesia from there, possibly by Polynesians who had traveled to South America and back. Thor Heyerdahl proposed in the mid-20th century that the Polynesians had migrated from the northwest coast of Canada by large whale-hunting dugouts, and from South America on balsa-log boats. Many anthropologists have criticised Heyerdahl's theory, including Wade Davis in his book "The Wayfinders". Davis says that Heyerdahl "ignored the overwhelming body of linguistic, ethnographic, and ethnobotanical evidence, augmented
Thor Heyerdahl also criticised Heyerdahl's theory in his 2009 book "The Wayfinders", which explores the history of Polynesia. Davis says that Heyerdahl "ignored the overwhelming body of linguistic, ethnographic, and ethnobotanical evidence, augmented today by genetic and archaeological data, indicating that he was patently wrong." A 2009 study by Norwegian researcher Erik Thorsby suggested that there was some merit to Heyerdahl's ideas and that, while Polynesia was colonized from Asia, some contact with South America also existed. Some critics suggest, however, that Thorsby's research is inconclusive because his data may have been influenced by recent population contact. However, more recent work indicates