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."
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 with short coats require virtually no grooming, just a brush and wipe down every so often. Pet dogs with long coats require either regular clipping every eight weeks or so (where their coats are clipped short) or there long coats need to be brushed practically every day. Show dogs, or dogs with long coats, require daily brushing or else there coat will become matted and tangled. Not only can it hurt your dog if he has tangled and matted hair, but it will also become dirty and he will look shaggy and ugly if you do not regularly brush his coat.
Some dogs will patiently put up with little children who pull their ears or accidentally poke them in the eyes, while others will not and map nip or bite back in defense. So if you want a dog who is excellent with children avoid breeds which may have a dominance streak or that have short tempers.