For thousands of years dogs have been bred. From time to time humans have done inbreeding even from their own ancestral lines and also by mixing them from various lines. Over the centuries the whole breeding process is continuing until the present day, resulting in a huge genetically diversity of all types of dogs, breeds and hybrids, no other mammal can present. Furthermore no speciation developed, despite the appearance of a wide variation of dogs no other animal could obtain. Just compare the extreme difference between a Chihuahua and a Great Dane.
Generally there is a wide interpretation of what is called “breed”. Breeds are actually categorized by a functional type from which a breed has developed. The most of the breeds are traditional breeds with a very long history, who are registered. There are some rare breeds, who have also their own registries, but some new breeds are still under development. There are even a lot of dog breeds, who are in danger to extinct. There are a few cases, where the origin of breed overlaps the frontier of two, three or more countries. As the general rule the dog is listed in the country in that he is most commonly associated, according to the FCI (Fédération Cynologique Internationale), by the designated country of the dog. There are some dogs, who have an uncertain origin, therefore they are getting classified under several countries.
There are subcategories as working dogs, companion dogs, herding dogs, guard dogs, hunting dogs and sled dogs. Working dogs are for example lapdogs, who are used as therapy dogs. Companion dogs are just providing companionship and are known as pets and who are usually not used for specific tasks. Herding dogs are known as stock dog and they are working with livestock. They are also called pastoral dogs, who do not necessarily have to be trained in herding. Guard dogs defend the property of people. They are also named watch dogs or attack dogs. They bark aloud, when there is a presence of a possible intruder and alert in this way their owners. Hunting dog hunts with or for their owners. There are a lot of different types of dogs, who have the special hunting skills. Sled dogs are also named sledge dogs or sleigh dogs, who were bred historically for pulling sleds to transport or haul supplies into areas which are inaccessible by another method.