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 great diversity in race, nationality, religion and political viewpoint in order to demonstrate that at least on their own little floating island, people could cooperate and live peacefully. Additionally, the expedition took samples of marine pollution and presented their report to the United Nations. Heyerdahl built yet another reed boat, "Tigris", which was intended to demonstrate that trade and migration could have linked Mesopotamia with the Indus Valley Civilization in what is now Pakistan and western India. Tigris was built in Iraq and sailed with its international crew through the Persian Gulf to Pakistan and made its way into the