world zone, in the Americas, was settled at least by fifteen thousand years ago but was largely cut off from Eurasia when the Bering Strait was flooded at the end of the last ice age. In recent millennia, a fourth zone would emerge in the Pacific. Western islands such as the Solomons may have been settled as early as forty thousand years ago, but islands farther to the east and south (including New Zealand, Hawaii, and Easter Island) were settled during a remarkable series of seaborne migrations that began just thirty-five hundred years ago. The existence of different
