The study found distinct genetic clusters within modern dogs that largely corresponded to phenotype or function. These included spitz-breeds, toy dogs, spaniels, Mastiff-like breeds, small terriers, retrievers, herding dogs, scent-hounds, and sight-hounds. There were 17 breeds that conflicted with phenotype or function and these were thought to be the result of crossing some of the other phenotypes. As in a 2004 study that found 9 ‘ancient breeds’ to be genetically divergent, the study found 13 breeds that were genetically divergent from the modern breeds: the Basenji, Saluki, Afghan hound, Samoyed, Canaan dog, New Guinea singing dog, dingo, Chow Chow, Chinese Shar Pei, Akita, Alaskan malamute, Siberian husky and American Eskimo dog. Results also indicated that the Basenji had recent admixture with Middle Eastern wolves.
In Great Britain the Kennel Club maintains a list of “vulnerable native breeds.” This refers to breeds that were developed in the UK which register fewer than 300 individual dogs per year. There are currently about 29 breeds on this list, with more breeds on the Watch list, meaning they are close to Vulnerable status. Although the Kennel Club in Britain registers fewer dogs than we do in the U.S., the situation with purebred dogs in the U.S. is similar. While the Labrador Retriever - the top dog registered by the AKC for over 20 years - has tens of thousands of individual registrations every year, other breeds have far fewer numbers. Beyond a few popular breeds, most breeds have relatively small numbers of dogs registered each year. We have many breeds in the United States which register only a few hundred individual dogs per year.
Dogs have been selectively bred for thousands of years, sometimes by inbreeding dogs from the same ancestral lines, sometimes by mixing dogs from very different lines. The process continues today, resulting in a widening in appearance without speciation, "from the Chihuahua to the Great Dane."
Today there are over 400 recognized breeds of dogs in the world. Many of them have historical origins dating back hundreds, even thousands of years. Wherever humans have lived, dogs have been alongside them performing various tasks. One of the reasons dogs have been such a successful species is because they are so adaptable. They have made themselves useful in countless ways to humans so we kept feeding them, providing shelter for them, and, yes, breeding them. It’s no accident that we have dogs able to hunt, herd, guard, track, and do so many other things at an expert level. Humans figured out early on that if you bred dogs that were good at these things, you would get offspring that were also good at doing them. All of these jobs performed by dogs were necessary for our own species to survive. It’s no secret that we owe a lot to dogs, just as we do to other animals.