I have benefited enormously from the help and insight of many colleagues, who have provided data, interpretations and counter-arguments for the many theses I pursue in the book. Foremost among them is Peter Underhill, whose careful work on the population genetics of the Y-chromosome has allowed me to tell this story. It was Peter and his colleagues at Stanford who discovered most of the markers discussed in this book, and the field owes him a debt of gratitude. I have also learned a great deal from my work with Li Jin, a fountain of knowledge on the population history of east Asia, and from interactions with my Oxford colleagues Walter Bodmer, Tatiana Zerjal, and Chris Tyler-Smith, who have challenged me on various genetic details and always make for very stimulating company. Nadira Yuldasheva and Ruslan Ruzibakiev have been friends and co-workers during countless months of sample collecting in remote parts of Asia, and throughout the years of labwork that followed – bolshoi spasibe. Merritt Ruhlen and Richard Klein were happy to discuss their work on linguistics and paleoanthropology, respectively, which was invaluable. Thanks also to Lluis Quintana-Murci, Matthias Krings and Mark Seielstad for in-depth explanations of their work over long, boozy meals in Paris, London and Boston – the hangovers were worth it. My colleagues at Tigress Productions in London, who believed in this project during the long television commissioning process, have created a wonderful film – thanks to Jeremy, Justine, Clive, David, Ceri, Jackie, Aidan, and Martin. We were lucky to have a great producer, Jennifer Beamish, whose sharp mind acted as a perfect sounding-board for many of the ideas in this book. A special thanks to my editor at Penguin, Stefan McGrath, whose enthusiasm for this project has never waned, and who was able to make deft use of both carrot and stick in order to get me to finish the book on time during our long filming schedule – I owe you a few beers. And finally, apologies to my wife, Trendell, and to my daughters, Margot and Sasha, for my long absences during this project. Even when I was home, I was often preoccupied – thanks for bearing with me.