Since 1977, archaeologist Tom Dillehay has been unearthing conclusive evidence of human habitation in the Americas at least 15,000 to 20,000 years ago, settling a bitter debate and demolishing the standard scientific account of the settlement of the Americas. The question of how people first came to the Americas is now thrown wide open: the best guess is that they arrived from a variety of places, at many different times and by many different routes...