Rescuing a dog is indeed a noble gesture, even if there will never be enough humans to save every abandoned dog. But for the health of their daughter, the Obamas want a purebred dog. And last time I checked, Portuguese water dogs weren't turning up at the pound with any regularity.

Most of the purebred dogs that end up in shelters come by way of reckless backyard breeders or puppy mills, where dogs are routinely inbred, bred so narrowly for looks that they can't breathe properly, or bred with no thought for their health at all. Responsible breeders track their puppies assiduously and take them back if they don't work out. They don't put their dogs up for rescue, they "re-home" them.

If the Obamas find a Portuguese water dog in need of re-homing, good for them -- no doubt it will be theirs for the asking. But that dog won't qualify as a rescue. And it shouldn't have to.

For the record, I rescue dogs. I rescue, in fact, the kinds of dogs that end up in shelters in droves: Yippie, wild-eyed terriers and the much-maligned American Staffordshire (pit) bull terriers. I take them in, train them and keep them with me for longer than a decade; I work through their tendencies to bolt or their fears of men in baseball caps until they accept the compromises of life with humans. I am well set up for the task: My tolerant, dog-loving husband and I have no children; I love dogs that would drive sane women mad; and I have the tenacity to work with them.

But I also love purebred dogs and the whole notion that we humans have bred dogs for certain tasks. I love Newfoundlands that save drowning children, border collies that live to herd, brave terriers driven to hunt rats. And I despair that we may be heading into a world in which breeding dogs to do what dogs do -- work with, and beside, and indeed even for, human beings -- is considered, by some crooked measure, cruelty to animals.

There is something far worse than a family acquiring a dog from a conscientious breeder, and that's a family rescuing a dog that turns out to be fundamentally unstable or just plain unsuited to life with a family.

Childhood dogs shape attitudes toward animals for life; they can make kids lifelong advocates for animal welfare or create in them an ineluctable fear. A family that adopts a dog that incorrigibly nips children's hands, eats expensive furniture or lunges at other animals might at best end up investing in an expensive trainer. At worst, the dog ends up back in the shelter or on the street, leaving a family forever wary of canines.

In January, one month after the death of a beloved pit bull I rescued from the pound 13 years ago, I took in a 5-month old American Staffordshire named Tabitha. She is, from what we can tell, sane and hearty, a natural retriever, psychologically stable enough that neither ear-pulling nor toe-fondling nor the taunts of her Cairn terrier housemate, Thomas, faze her.

But Tabitha is still a puppy, and having lived with dogs -- seven in total -- nearly all my life, I know that puppies harbor secrets in their DNA. What we know about Tabitha is all good, but we could scribble it on a sheet of notebook paper. What we don't know could fill volumes.

We don't, for instance, know what her parents were like. We don't know if she harbors the gene for a debilitating neurological condition called ataxia that is common in her breed. Will she continue to put up with our ambushing cats? With the squeals of our friends' children? We think so, and we will work with her no matter what. If we had children to worry about, however, it might be different.

Symbolically, it would be nice if the Obamas could rescue a dog. But to insist that the only good dog is a rescued dog is to relegate our future with the canine species to random relationships in which humans are forced to settle for whatever renegade breeders produce and fail to care for.

And let it be said that the reason there exists such a thing as a Portuguese water dog at all, or any dog with a hypoallergenic coat and a game temperament, is not a happy accident but a triumph of the selective breeding humans have been practicing with canines for millenniums -- the very practice so many people who claim to care about dogs would prefer to see turned into a crime.

Judith Lewis is an environmental journalist and contributing editor to High Country News.