DOGS can be seen walking along our city parks, romping in backyards, wandering stray in search of food, napping in our living rooms, begging at our tables—just about anywhere in society. In most places, they are known as the family dog. It is estimated that there are 150 million members of the canine population in the world, and there is great variability, with more than 300 breeds throughout the world—from the Great Dane at 150 pounds (67.5 kilograms) to the Chihuahua at 1.5 pounds (0.68 kilogram). One of the things all canines have in common is their instinctive behavior as pack animals. A pack is a group of animals that live together all dependent on one another for protection, companionship, mates, babysitters for the young, and hunting companions. Archaeologists have found evidence of dogs on Earth 25 to 30 million years ago. Since then, humans have become the leader of the pack for domestic dogs. DOGS, a title in the popular series Pet Library, is an illustrated, practical guide to animals we love so much that we make them part of the family.