When Captain Samuel Wallis became the first European to land at Tahiti in June 1767, he left not only a British flag on shore but also three guinea hens, a pair of turkeys, a pregnant cat, and a garden planted with peas for the chiefess Purea. Thereafter, a succession of European captains, missionaries, and others planted seeds and introduced livestock from around the world. In turn, the islanders traded away great quantities of important island...