Alan Alda in Scientific American Frontiers
"Coming to America"
Who were the first Americans, and when did they arrive? Did they get here by land or sea? Did a single group populate the continent, or did many? Experts used to agree that the first Americans walked across the Bering land bridge from Asia about 12,000 years ago, then found their way south, eventually colonizing all of North and South America. But exciting recent finds at sites on both continents have triggered new theories. Alan Alda tries to find out who's saying what, and why. D