20,000 years ago, people crossed a great land bridge from Siberia into Western Alaska and then dispersed southward into what is now called the Americas. Until we venture out to other worlds, this remains the last time our species has populated an entirely new place, and this event has been a subject of deep fascination and controversy. No written records--and scant archaeological evidence--exist to tell us what happened or how it took place. Many...

From the Siberian permafrost to balmy California, scientists across the globe are working to resurrect all kinds of extinct animals, from ones that just left us to those that have been gone for many thousands of years. Their tools in this hunt are both fossils and cutting-edge genetic technologies. Some of these scientists are driven by sheer curiosity; others view the lost species as a powerful weapon in the fight to preserve rapidly changing ecosystems....