Few people have more intimate knowledge of my dog than Dr. John Trujillo does -- he did, after all, relieve Ace of his reproductive bits -- but as far as what Ace might be, breed-wise, Trujillo had never volunteered a guess and didn't particularly care.

He gets the question from many mutt owners. "Lots of people want to know, but a lot more don't care," he said. "As long as it's a happy dog, that's all they care about."

It's all I really care about, too. But, being curious -- not to mention being frequently bombarded with the question myself -- I was on a mission to find the answer. So I demanded a diagnosis.

"What do I think he is? He looks like shepherd and Akita," said Trujillo, who runs Light Street Animal Hospital. "The reason I say Akita is because his tail is twisted like an Akita, but you don't see this coat on an Akita; you see this coat on a German shepherd. But more of what I see is Akita."

Dr.Thomas C.Jett, a veterinarian who helps out at the Baltimore Animal Rescue and Care Shelter, known as BARCS and formerly the city animal shelter, sized up Ace and offered the same opinion -- shepherd and Akita.

For a third,we went to Dr. Jill Shook at Citypets Veterinary Care and Wellness. "I would say, just based on his coloring and the length of his coat, there's some German shepherd, probably; possibly, with the tail, a little bit of chow. But the shape of his head fits in more with Labrador retriever, or maybe a little bit of Rottweiler," Shook said.

In the year and a half I've had Ace, I've heard dozens of other guesses -- Rhodesian Ridgeback, retriever, collie,chow, Catahoula, Kangal and redbone coonhound, to name just a few.

There are more than 400 dog breeds, 162 of which are recognized by the American Kennel Club; and there were only two ways to find out how many of those might be in Ace.

One, I could find his parents -- unlikely since the shelter I got him from knew only the name of the man who found him wandering the streets, and it wasn't giving me that. Two was through his DNA,which I had already harvested and sent to the lab.

As I waited for the results, I went from pondering what breeds are in Ace to the larger question:What is in a breed? The answer, when you get right down to it, is mutts.

With the exception of the wolf, every breed of dog is, or at least at one time was, a hybrid of some sort. The first German shepherd, the first Doberman pinscher came from other kinds of dogs-- and most were shaped, if not designed, primarily by the hand of man.

"In the beginning, all dogs were mixed," said Raymond Coppinger, professor emeritus of biology at Hampshire College and co-author of Dogs: A Startling New Understanding of Canine Origin, Behavior & Evolution.

"Purebred is a terminology that started off in the end of the 19th century with the idea that rich people were better than anyone else, leading to all the talk of genetic purity and eugenics," Coppinger said. "Of course, it was one of those things that never worked on people, and efforts to impose it were all bad news."

After World War II, purebred dogs surged in popularity, Coppinger said.

"As a boy growing up,my goal in life was to be able to get a purebred dog. Having read Lassie, I thought that was going to be something special. We were all kind of duped into that belief." Coppinger, in his latest book, cowritten with his wife, Lorna, criticizes some breeders, especially those breeding to win dog shows.

"Breeders and owners forget what the historical dog looked like," he wrote. "They select for the exaggerated form. They select for the really big ones. They select for the flattest face. They select for the longest face.…Each breed takes on an unnatural shape, becoming a freak of nature. They are loved the way the hunchback Quasimodo was loved--a dichotomy between the grotesque form and the honorable personality.

"I believe the modern household dog is bred to satisfy human psychological needs, with little or no consideration of the consequences for the dog. These dogs fill the court-jester model of pet ownership."

He was particularly critical of dog shows: They "are comparable to human beauty-queen pageants. Compare each individual with the others in the show and see which one comes closest to some arbitrarily designated, idealistically 'perfect' form."

As for testing my dog's DNA, Coppinger didn't have much respect for that plan, either.

"You're wasting your money, and somebody out there is preying upon you to believe in all this stuff," he said. "Go and have someone do your genealogy; you can hire somebody to do that. What does it mean? It doesn't mean anything. But if that makes you happy, do it."

Coppinger's views, cranky as they might sound, aren't coming from right field. They are echoed by James Serpell, associate professor of humane ethics and animal welfare at the University of Pennsylvania and author of In the Company of Animals: A Study of Human-Animal Relationships.

"Pedigree dog breeding is an exercise in eugenics, and the efforts to maintain racial purity have had moderately to severely damaging effects," he said. Many bulldogs, for example, as a result of efforts by breeders to produce animals with even larger heads, must now be born by Caesarean. "There's a strange aesthetic going on here. The strategy is not to produce healthy dogs, it's for producing dogs of a uniform physical type. … It's all about just the look."

The trend, while driven by breeders and dog shows, is fed by consumer demand, he said. "A lot of people contemplating getting a dog actively seek out a particular breed. It's like buying a car; it's like owning a Corvette. They have a particular notion of this particular breed being just right for them."

Sometimes that's based on sound reasoning; sometimes it's based on vanity -- "the breed may be seen as the perfect accessory," he said.

Serpell, the owner of a mutt of undetermined origin, said he, too, is frequently asked what breed his dog is. He usually responds with a made-up breed.

"Bosnian snakehound," he tells them. If you say it with enough authority, he has found, people often accept it.

I've toyed with that idea myself … South Baltimore alleyhound, Formstone terrier, shorthaired Patapsco retriever.

I want the real answer, though, and impossible as it might be to find, Ace and I aren't done sniffing around yet.