One reason why some dogs grew up to look different from other dogs was that they lived in different kinds of climate.

For example, Wild Dog and his children, grandchildren, and their grandchildren who lived for many hundreds of years in a northern country all needed thick coats. Without these, they died of the cold. Only the thick-coated dogs survived, and gradually a thick-coated kind of northern dog developed. Breeds like the Eskimo dog, who pulled sleds in the Arctic, and the Saint Bernard, who saved lost mountain climbers in the snowy Alps, developed in the cold countries. But if Wild Dog’s descendants lived for hundreds of years in a hot climate, they developed thin coats of hair, or sometimes none at all, like the Mexican Hairless.

The kind of country in which the early dogs lived also accounts for different breeds. Dogs that grew up in countries like Egypt, where there were flat plains and desert, all developed long legs and could run swiftly. This was the only way they could catch enough to eat, and also the only way they could save themselves from being eaten by larger animals, because there is no place to hide on a desert. Some of our fastest dogs today, like the Saluki, originally came from such countries.

Then there were dogs who grew up in a land that was covered with dense forests, like early England. These dogs could catch their food animals only if they were small and tough and could chase rabbits through the thick underbrush or dig for other small game in the ground. And the only way they could save their own lives when threatened by their enemies was to be so quick and so little that they could scurry into hiding places where larger animals could not follow. From dogs who lived in such countries come most of the breeds known as terriers.

And as one breed developed differently from another because of the influence of climate or country, they also developed differently because of the influence of man. When men learned the many ways that dogs could be useful, they decided to try to reproduce these valuable animals especially for the purpose for which they were most needed. For instance, if one man had a large flock of sheep, he would choose a father sheep dog who had proved to be the most alert to bark when a stranger came too close. And he would choose a mother sheep dog who was the smartest in guiding the sheep quickly back into the fold. The man hoped that at least some of their puppies would be able to do both these things equally well, and so grow up to be even better sheep dogs than their parents. These puppies, in turn, might be the parents of still better sheep dogs. By such experimenting, for hundreds of years, the shepherd breeds we now know were eventually developed.

By the same process, men tried to raise good watchdogs, hunters, or other work dogs. Finally, the more than two hundred different kinds of dogs in the world today came into being. Now there are about twenty million purebred dogs in the United States alone! (When a dog’s mother and father are both of the same breed, he is called a purebred dog.)

These purebred dogs we know today have been classified by experts into six groups, on the basis of the special abilities of the different breeds. These six groups are the Sporting Group, the Hound Group, the Working Group, the Terrier Group, the Toy Group, and the Non-Sporting Group.