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That's just the final polish, though: no dog can hope to be a champion without conforming to a very narrow standard of physical perfection set by individual dog clubs and ratified by the AKC. And customer-conscious breeders have obliged by creating prizewinning dogs with specific traits, such as long ears in cocker spaniels or sloping hips in German shepherds.
Biologically, this is just asking for trouble. For one thing, the characteristics judges and clubs have decreed to be gorgeous can themselves be bad for the animals' health -- huge heads on bulldogs that make it difficult for them to be born naturally, for example, or the wrinkled skin on Shar-Peis that sets them up for rashes. For another, the best way to produce a puppy with a specific look is to mate two dogs who have that same look. As with any species, though, the closest resemblances are found among the closest relatives. So breeders often resort to inbreeding, the mating of brothers and sisters or fathers and daughters. Or they "line-breed," having grandparents mate with grandchildren or cousins with each other. "If we did that in humans," says Mark Derr, who wrote a scathing indictment of America's dog culture for the March 1990 Atlantic Monthly, "we'd call it incest."
Both practices increase the likelihood of genetic disease. It is not that purebreds have more defective genes than other dogs, or that inbreeding - somehow causes healthy genes to go bad. Most hereditary disorders in dogs are caused by recessive genes; as long as an animal has a good copy of the gene from one parent, it will override a bad copy from the other parent. But if both parents pass on the same bad gene -- which is more likely if mother and father come from the same family -- the puppy has a problem.
The problem intensifies with what experts call "the popular sire effect," the result of a single desirable male's being used to sire a large number of litters. Says Michigan State's Schall: "If it is later determined that the male that looked perfect has a genetic disease, he will have dispersed it widely before it gets discovered."
Hereditary weakness can be introduced even when there is no underlying genetic defect at all. The biological interplay between individual genes can be extremely complicated, and breeding to enhance one characteristic can have unintended consequences. Vets believe the retinal disease that afflicts most collies may fall into this category. The gene responsible may lie very close to the one that gives collies their long noses and closely set eyes -- traits that have been deliberately emphasized by breeders. Says Dr. Donald Patterson, chief of the medical genetics section at the University of Pennsylvania's School of Veterinary Medicine: "Many people have bred dogs for desired traits, but in the process of doing this they have also got undesirable ones. The objective should be to combine breeding for good traits with more careful planning to get rid of genetic defects. Unfortunately, not much attention has been paid to that."