Drought, flood, and temperature changes could certainly push people to move on. Climate change also affects the food supply, and anthropologists have assumed that people came to the Americas because they were following food on the hoof.
Now our understanding of when people reached the Americas—and where they came from—is expanding dramatically. The emerging picture suggests that humans may have arrived in North America at least 20,000 years ago—some 5,000 years earlier than has been commonly believed.
