Book excerpt: The bestselling author of Dog Sense and Cat Sense explains why living with animals has always been a fundamental aspect of being human. In this highly original and hugely enjoyable work, John Bradshaw examines modern humans' often contradictory relationship with the animal world. Why, despite the apparent irrationality of keeping pets, do half of today's American households, and almost that figure in the UK, have at least one pet (triple the rate of the 1970s)? Then again, why do we care for some animals in our homes, and designate others only as a source of food? Through these and many other questions, one of the world's foremost anthrozoology experts shows that our relationship with animals is nothing less than an intrinsic part of human nature. An affinity for animals drove our evolution and now, without animals around us, we risk losing an essential part of ourselves.