Human migration

Sixty thousand years ago perhaps as few as “a couple of hundred people,” members of the species Homo Sapiens, departed “humanity’s birthplace in the Great Rift Valley of East Africa,” and ventured out of Africa and crossed into Arabia. Some of their progeny walked north into Europe, but others headed east into Asia and down to Australia, or crossed the Bering Sea and walked south into North and South America. Now, after 2,500 generations, human beings claim the Earth.

The National Geographic writer Paul Salopek calls this epic journey “by far our greatest voyage.” He writes that those first Af...