Of the world's dogs, less than two hundred million are pets, living with humans who provide food, shelter, squeaky toys, and fashionable sweaters. But roaming the planet are four times as many dogs who are their own masters--neighborhood dogs, dump dogs, mountain dogs. They are dogs, not companions, and these dogs, like pigeons or squirrels, are highly adapted scavengers who have evolved to fit particular niches in the vicinity of humans. In What Is a Dog? experts on dog behavior Raymond and Lorna Coppinger present an eye-opening analysis of the evolution and adaptations of these...