We have an extraordinary relationship with dogs - closer than with any other animal on the planet. But what makes the bond between us so special? Research into dogs is gaining momentum, and scientists are investigating them like never before. From the latest fossil evidence, to the sequencing of the canine genome, to cognitive experiments, dogs are fast turning into the new chimps as a window into understanding ourselves. Where does this relationship come from? In Siberia, a unique breeding experiment reveals the astonishing secret of how dogs evolved from wolves. Swedish scientists demonstrate how the human/dog bond is controlled by a powerful hormone also responsible for bonding mothers to their babies. Why are dogs so good at reading our emotions? Horizon meets Betsy, the world's most intelligent dog, and compares her incredible abilities to those of children. Man's best friend has recently gone one step further - helping us identify genes responsible for causing human diseases.