Book excerpt: Travel backward through time from today's scattered billions to the handful of early humans who lived in Africa 60,000 years ago and are ancestors to us all. In Deep Ancestry, scientist and National Geographic explorer Spencer Wells shows how tiny genetic changes add up over time into a fascinating story. Using scores of real-life examples, helpful analogies, and detailed diagrams and illustrations, he explains exactly how each and every individual's DNA contributes another piece to the jigsaw puzzle of human history. The book takes readers inside the Genographic Project—the landmark study now assembling the world's largest collection of DNA samples and employing the latest in testing technology and computer analysis to examine hundreds of thousand of genetic profiles from all over the globe—and invites us all to take part.