Gun dogs were developed in varying sizes from relatively small spaniels to medium-sized setters, retrievers and pointers. With the exception of the Pointer and the relatively modern Labrador, most gun dogs developed in the United Kingdom (the Clumber Spaniel and Golden Retriever for instance), have medium to longish coats whereas several European ones (like the German Wire and Shorthaired Pointers, the Hungarian Vizla and Weimaraner) have short or wiry coats. Nearly all have developed shapes that are slightly longer than they are tall with sleek ribbing and limited depth of chest. Coat color may vary because it is considered relatively unimportant.
Sighthounds were developed along Greyhound lines for speed at the gallop. An absence of massive bone or great substance, plenty of lung room and good eyesight were desirable. Such breeds have relatively long legs and considerable "tuck-up" in the loin. Other hounds were usually short-coated dogs selected for their pronounced scenting ability and were of various sizes depending upon the prey sought. Speed was a minor consideration other than in Foxhounds that were always geared toward endurance.
Terriers were essentially small, somewhat square dogs without layback of shoulder sought in most other breeds. Originally, terriers were specifically used down holes or in confined spaces where speed of movement was not required.
Some breeds were developed as bull or bear baiting animals. They needed to be shortcoated with small ears and fairly short tails but with massive jaws, often undershot to allow the dog to grip but still breathe. They were medium sized and agile with good length of leg and very muscular. When these barbaric sports were banned the "bull breeds" developed in no set direction since their role had disappeared. But Bull Terriers, Boxers, Bulldogs and American Pit Bulls are descendants of these original baiting breeds. Of course, fighting potential had been selected into such breeds and, once their roles changed, these potentials had to be modified in other less fearsome directions. In the same way, since fighting was no longer undertaken, agility became less necessary. Exaggeration by man led to such extreme types as the Bulldog, now vastly different from its bull-baiting progenitors.
Most of the selection undertaken in the development of breeds was done by trial and error. These animals that did a job well were used to produce the next generation. Failures were discarded from breeding programs. In the twentieth century. breed Standards have been used as yardsticks by which breeds are judged. As a consequence most dog breeds have been selected for so-called physical excellence regardless of function. For example, early Bernese Mountain Dog breeders sought a cleft nasal palate in the belief that it made the dog look more ferocious when, in fact, such a feature was harmful to the dog's health and eventually selected against. Similarly, the breed Standard called for a chest coming "at least to the elbow" and thus, in theory, permitted a chest that reached to the ground. The Bulldog Standard sought a head as large as possible, seemingly oblivious to the fact that this was inevitably going to lead to a high percentage of Caesarean births. Most Standards were drawn up in the country where the breed developed and simply translated into other languages as the breed spread. In modern times collaboration between kennel clubs has meant that many flaws in Standards have been removed, although many breeders may still be seeking to reproduce dogs that conform to ideals that no longer hold good and were not sound in the first instance.
The dog has been changed more in the last one hundred years than it had changed in the thousands of years preceding this century. Much of the momentum for change stemmed from the show ring and the desire of breeders to produce animals of a specific breed or type which would win in the ring. Although it would not be true of every breed, present day examples of certain breeds have little in common with their ancestors of a century ago. The modern Chow Chow bears minimal resemblance to those of 1900, in this same way the Bulldog no longer resembles its bull-baiting ancestors. In contrast, the Border Terrier of today is little changed from those which originally formed the breed. Similarly modern German Shepherd Dogs generally have better characters and are more athletic and functionally correct than those which were introduced to the United kingdom in 1918. Much of this change has only occurred in the past two decades.
In some breeds there has been a dichotomy between the dogs used for working and those bred primarily for the show ring. This is perhaps most obvious in some, though not all, breeds of gun dog. Labrador Retrievers used for working purposes tend to be smaller, lighter and faster than the dogs seen in the show ring although, as in any breed, there are exceptions to this general rule. If the working and show types were to be bred apart with little or no intermixing then in due course they would emerge as two distinct breed types of differing appearance, behavior and quite distinct bloodlines in the immediate generations.