The role of salmon in human migration to North America

How did humans populate what we now call the Western Hemisphere? The old theory said that humans walked across an historic land bridge from Asia to Alaska in search of big game. A more recent hypothesis posits that ancient humans paddled along the coastline from river to river in pursuit of salmon. One anthropologist calls it the "fishing link." National Geographic Explorer Paul Salopek has been looking into this as he paddles down Alaska's coastline into British Columbia, and joins Host Marco Werman to explain what he's learned.