We sat down with award-winning science journalist and author, Alan Weisman to talk about his best-selling book "The World Without Us." Find out what prompted him to write the book and where Weisman thinks the world is headed if we don't control our population explosion. Weisman is Laureate Associate Professor in Journalism and Latin American Studies at the University of Arizona. Learn more about his work here. The world population is now: over 6 billion.