Some 20,000 years ago, people crossed a great land bridge from Siberia into Western Alaska and then dispersed southward into what is now called the Americas. No written records—and scant archaeological evidence—exist to tell us what happened or how it took place. Making use of cutting-edge genetic research, anthropologist Jennifer Raff tells the story of who the first peoples in the Americas were, how and why they made the crossing, how they dispersed south, and how they lived.