Dogs descended from wolves and were first domesticated by humans about 15,000 years ago.http://www.dogfacts.org/dog-facts.htm The term dog may also be applied to various wild species of the canine family such as hyenas and coyotes.

There are over 300 dog breeds in the world.http://www.sciencedaily.com/releases/2010/03/100301201937.htm?sms_ss=digg This figure includes the 170 breeds recognized by the American Kennel Club.http://www.sciencedaily.com/releases/2010/03/100301201937.htm?sms_ss=digg All of these breeds belong to the species Canis familiaris.http://www.pbs.org/wgbh/evolution/library/01/5/l_015_02.html

Dogs have been selectively bred by humans to create breeds that have special talent in performing particular functions such as pulling sleds, herding livestock or retrieving game. Breeders may also choose to breed animals to produce certain physical and behavioral characteristics including coat color and texture, temperament, ear shape and tail length.

Although their appearances may differ to the extreme, all dogs remain in the same species which means that they can interbreed with one another. Although pure-bred dogs have a higher financial value, mixed breed dogs are still purchased outside of dog competitions.

The American Kennel Club(AKC) recognizes six classes of dogs: sporting, hound, working, terrier, toy, non-sporting, herding and miscellaneous.http://www.akc.org/breeds/miscellaneous_class.cfm The AKC states that there are hundreds of other breeds worldwide that could be pure-breds.http://www.akc.org/breeds/miscellaneous_class.cfm However, the miscellaneous class only contains nine of them. They are American English Coonhound, Cesky Terrier, Chinook, Entlebucher Mountain Dog, Finnish Lapphund, Norwegian Lundehund, Rat Terrier, Russell Terrier, Treeing Walker Coonhound and Xoloitzcuintli. http://www.akc.org/breeds/miscellaneous_class.cfm

The sporting and hound class contain active dogs that perform well in outdoor field and hunting activities.http://www.akc.org/breeds/sporting_group.cfm http://www.akc.org/breeds/hound_group.cfm Working dogs actually perform tasks like pulling sleds or protecting property.http://www.akc.org/breeds/working_group.cfm The herding class of dogs were breed to herd livestock.http://www.akc.org/breeds/working_group.cfm