According to the American Pet Products Manufacturers Association, more than 43 million U.S. households keep nearly 74 million dogs as pets and de facto family members. We love our dogs and are often willing to spend exorbitant sums for the perfect pup. The American Kennel Club estimates that one in four dogs are purebreds.

Individual dog breeds are so familiar to us, it's easy to forget that they are just races of a single species -- races that we've invented. In the wild, nature selects for particular traits and behaviors. In dogs, we've stepped in for Mother Nature and made our own selections.

Those selections have produced a species that comes in shapes and sizes that are all over the map. English mastiffs tip the scales at up to 200 pounds, while Chihuahuas weigh in at less than six. The faces of a bulldog and a basenji give no hints that they belong to the same species. "Some people design dogs like it's an art form," says Coren.

Unfortunately, those art forms often beget health problems, linked not to genetic diseases but to the dog's body shape. We've selected for physical traits in dogs that would never have originated in nature because they're not adaptive. The English bulldog is a classic example, says Raymond Coppinger, an evolutionary biologist at Hampshire College in Amherst, Mass., and co-author (with his wife, Lorna) of "Dogs: A Startling New Understanding of Canine Origin, Behavior, and Evolution."

Bulldogs' heads are so big that they cannot fit through the birth canal, and their puppies must be delivered by cesarean section. And their radically flattened faces lead to deformed respiratory machinery, Coppinger says. As anyone who's come into contact with a snorting, snoring bulldog knows, they have a hard time breathing. Such a hard time, in fact, that they often have abnormally low levels of oxygen in their bloodstreams. "The dog isn't adapted to be that shape," he says. "The biology can't go there."

Some of our aesthetic choices have no apparent bearing on a dog's well-being; chances are, fur color doesn't much matter to a dog that doesn't have to camouflage itself in the wild. But in other cases, our choices could very well affect a dog's quality of life. Is it animal cruelty to create teacup breeds that are so small their mouths can't support a healthy set of teeth? Or to engineer Chinese Shar-Peis whose absurdly wrinkled skin harbors ulcers and mange?

Breeders themselves sometimes debate where to draw the line in shaping a dog's anatomy, says Patrick Venta, a professor of veterinary medicine at Michigan State University and a collaborator on DogMap, one of several canine genome projects. "If you breed to the extreme, you enhance the features of the breed, but if you push too far, it can create some type of health problem for the dog," he says. "There will be gray areas."

While much of current genetic research aims to benefit human medicine, a large number of scientists are working to improve the health of our favorite pet. Dogs suffer from an impressive collection of genetic diseases and disorders, thanks to a high incidence of inbreeding. Breeds such as Labrador retrievers and Afghan hounds are crippled by hip dysplasia, golden retrievers are prone to a specific type of cancer, and narcoleptic Dobermans fail as watchdogs when they topple over into a deep and sudden sleep.

Those and other health issues may very well be resolved with genetics research, but cloning isn't likely to play much of a role in identifying and eliminating genetic disorders. "Cloning is incredibly expensive ... and extremely inefficient," says Venta. "There are so many things people involved in canine genetics can do without whole-organism cloning."

In 2001, scientists at Cornell announced a gene therapy technique to cure congenital blindness in Briards, a type of French herding dog. Traditional genetics work has so far produced tests for as many as 30 canine diseases, Venta says, allowing breeders to avoid carriers of conditions like narcolepsy and hip dysplasia.

Animal rights activists often condemn genetic tinkering as well as cloning. But whether a dog was conceived by breeding or by cloning, maybe they have it made. Sure, they suffer a little manipulation, but they get food and healthcare and a warm place to sleep. While we've exterminated the wolf from much of its original habitat, we've made sure to ferry our pampered dogs into this millennium and probably the next.

"We wouldn't have any dogs if humans over the course of thousands of years hadn't selected certain characteristics," Venta says. "We'd be living with wolves."

Coren agrees and even calls dog breeds vital. "My wife and I recently got a beagle and we knew he'd be sweet and kissy-faced and dumb as a stone," he says. "Predictability is what you're paying for when you pay for a purebred dog, and it's a good thing. You don't want to have to roll the dice." Cloning would take that purebred predictability and bump it up a notch.

Schlegelmilch first fell in love with the Afghan hound when one ran by her house more than 30 years ago. "I had never seen any animal quite so elegant and graceful," she says. Within six months she owned one, and she and her husband have kept them ever since. With each new dog, they know just what to expect: a graceful, athletic, independent dog that doesn't necessarily obey commands.

Schlegelmilch now deals with a trusted breeder who tests for genetic disease and produces healthy puppies. Not all breeders are so responsible. Schlegelmilch's first Afghan hound Desiree died at age 3 from the canine version of Huntington's disease, a genetic disorder. "In retrospect, I think she came from a puppy-mill type of breeder," she says.

The irony of cloning, says bioethicist Fiester, is that it may prove more ethical than breeding, as there's no dearth of evidence that breeders can be irresponsible. Commercial cloning companies can also be fairly certain that a person spending thousands of dollars on a clone will pamper her pet. The average dog breeder has much less reassurance that clients will be loving owners. "Our initial reaction [to cloning] may be a yuck factor against Frankenpets," Fiester admits. "But ethically, cloning may have a leg up."

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