"Today dogs are subject to a dangerous ‘game’ which involves irresponsible playing with one tiny aspect of their phenotype: the form. This leads to two important problems. Breeders are encouraged to inbreed in order to fulfil the requirements which lead to genetically homozygous populations, and the absence of selection for behaviour leads to the disappearance of breed-specific traits. Thus this trend brings nothing good for dogs in terms of their evolution because genotypes are being lost and genetic variability is decreasing."
Miklosi then cites P.D. McGreevy and F.W. Nicholas, whose article, “Some Practical Solutions to Welfare Problems in Dog Breeding,” 8 Animal Welfare 329-341 (1999), argued that breeds should not be considered closed populations, and dogs from other breeds should be crossed in. This would not change the appearance of the breeds, as breeding programs can create virtual breeds, as was done with the Pharaoh Hound (described by Miklosi, in another section of his book, as “probably a fake ‘look-alike’ recently created from different types of dogs”).
My father, M.E. Ensminger, would have agreed with the notion of breeding in animals from other breeds. In his treatises on Animal Science, Beef Cattle Science, and other books, he placed a high value on “hybrid vigor,” recommending that breeding programs regularly cross in other breeds to improve production. He had the advantage of working with the livestock production field where appearance is important, but other qualities, such as the amount of muscle that becomes hamburger, were even more important. Consequently, I'm not aware that he encountered much resistance to his arguments. (His books are still in print, being revised under a trust arrangement by staff at Iowa State University.)
Those concerned with dogs losing behavioral characteristics as a result of crossing in other breeds should consider the research of Kenth Svartberg, a Swedish scientist, who studied breed differences using tests of over 13,000 dogs in 31 breeds. Svartberg concluded that selection was often being dominated by show dog breeders, and that their programs were producing good show dogs, but that the behaviors correlated with the breed origins, often inconsistent with what is required for a show dog, were disappearing. Kenth Svartberg, “Breed-Typical Behaviour in Dogs—Historical Remnants of Recent Constructs?” 96 Applied Animal Behaviour Science 293-313 (2006).
My aunt, Lee Watts, was a well-known poodle breeder in Canada. She used to say that if you didn't get a purebred dog, "you don't know what you're getting." I still hear it when I go to obedience classes. What she didn't know, and what Svartberg's research indicates, that you may be getting the right form, but as time goes on you're not getting the same complex of behaviors. Domestication does not stay still for other factors, even if the form stays still.
Additional Note. The effect of letting show appearance dominate the breeding programs of a particular dog was decried long ago. Captian von Stephanitz, discussing the Scotch shepherd dog or collie in The German Shepherd Dog in Word and Picture (1923), noted that it is divided into "two varieties, a short smooth haired, and a long smooth haired kind, from which originated the long haired dogs so prized by the fancy breeders…. In the Shetland Islands, where the dwarf horse is bred, there is a dwarf variety of this collie.” He then says a picture of a long haired dog that was “a prize winner of some reputation, shows how far one-sided and exaggerated breeding may go till it becomes unnatural and a caricature. The collie of the fancy dog breeder is now only bred for beauty and is kept for luxury and show; with his slender small head and overbred face drawn out into an overlong nose—(this part from the tip of the nose to the division in the forehead is much longer than the cranium, while the proportion should be the reverse). Then there is the carriage of the ears, where only the upper third of them should tip over; but must only droop over that much, otherwise it is considered a great fault—(to the fancy breeder the erect eared Scotch dogs such as are also seen today are villainous rogues, worthy of death), and in conclusion the hair is everything…. The daily ‘toilet’—here the word must be understood in the English sense—of a collie beauty takes hours to perform; especially before an Exhibition.”
After discussing the show preparations that he finds offensive, Stephanitz then delves into the uselessness of the dog for real work:
“He lives more on the good reputation built up by the yeoman services of his ancestors, which he no longer knows how to perform. That is the meaning of the vacuous appearance of the shallow, unintelligent, ant-eater-like too elongated head…. The present day fancy Scotch dog with his slender needle like sharp teeth can tear very savagely and make serious wounds, but these qualities do not fit him for service with flocks and hers; and further, he lacks the strength necessary to stop and turn a stubborn sheep.”