Dogs belong to the dog family, Canidae. A dog is an animal that has lived with people as a pet for more than 10,000 years, longer than any other animal. During that time, breeders have developed about 400 dog breeds to perform various tasks, provide companionship, and please the human eye.
Most scientists believe that prehistoric human beings first valued dogs as watchdogs. Later, people realized that dogs could also be used for herding and hunting other animals. Over thousands of years, such breeds as collies, komondors, and pulis were developed to herd sheep, goats, and cattle. Hounds, pointers, retrievers, setters, spaniels, and terriers were bred for various kinds of hunting.
The intelligence, loyalty, and tracking ability that make dogs useful to herders and hunters serve people in other roles as well. For example, the police use dogs to track criminals and to sniff out illegal drugs and hidden explosives.
Dogs of all breeds provide company for human beings, and many breeds were developed for this purpose. These breeds include most of the small breeds called toy dogs, such as Japanese chins and Pomeranians. The companionship of a dog can contribute to a person's general well-being. Scientific studies have shown that petting a dog slows the heart rate and lowers the blood pressure of the person who is doing the petting.
Dogs assist disabled people in many ways. For example, they guide the blind and serve as "ears" for the deaf. In addition, dogs lift the spirits of patients in hospitals and nursing homes.