In the book, jenifer raff takes on a question that has vexed her field for centuries. When and how and why did humans migrate to the americas? For decades, archaeologists answered that question like this. Around 13 thousand years ago, small bands of hunters living in siberia followed mammoths and other giant beasts across a land ridge into alaska. They tried to move south, but were thwarted by an ice wall that was two miles tall and stretched from coast to coast. Eventually, though, the ice wall began to melt and a passable corridor opened up along the rocky mountains. Raced southward then, and within a few thousand years, their descendants could be