Describe how those early Americans survived.

How did human beings first come to North America? Across the Bering Strait, on foot? Down the "kelp highway" by boat? Across the Atlantic via the polar ice cap? And when did they reach here? 10,000 years ago? 40,000? Or were they always here, as the Navajo and other Native American tribes believe? In his new book, Atlas Of A Lost World, author Craig Childs sets off to test these different theories on the ground, traveling from Alaska to Chile, Canada to Florida. What he finds, despite the best efforts of archaeologists and the latest technology, still remains in many ways a mystery.

Speaking from his home in Colorado, he explains why many Native Americans reject the idea that their ancestors migrated from somewhere else; how an archaeologist nicknamed Dr. Poop believes he has identified the first human excrement in America; and why diversity seems to have been built into America's DNA.