The migration from Asia to North America across the Bering Strait (perhaps by land bridge) was a monumental event in human history. The process of overspreading the Americas took more than 1,000 years, or 30 generations. This might seem to confirm common sense—that slow travel was inherent in any great migration without wheeled vehicles across unknown terrain. Further thought shows that this process was remarkably fast—about 10 north-south miles per year, on average. The Americas were populated at an astounding pace, when one considers the physical limits of the human body and the physical features of the American continents. Legs of humans can move only so fast under the best of circumstances, and they work even slower over mountain passes or deserts. Populations spread through the diverse regions of the Americas (grasslands, eastern forests, coastal swamps) and needed to adapt to their new environments. The migrants’ lifestyle had evolved over the years to that of professional nomads ensuring that they would find the resources needed to survive.