“If you were going to get a pet / What kind of animal would you get?” Robert Creeley asked in the opening couplet of a poem that only occasionally rhymes or makes sense thereafter.

Never mind: An answer is provided in Sunday’s superb PBS two-part series, “Dogs That Changed the World: The Epic Story of Man’s Best Friend,” and I say this despite a theoretical fealty to my cat, which has been sprawled on the bed for, oh, about eight hours now. Amazingly, she hasn’t even asked for food. Nor did she bestir herself to join me in front of the television. A cat may look at a king, but it will not, apparently, deign to glance at a government-funded documentary about filthy, slobbering canines and their detestable, practically Stakhanovite work habits.

The film, narrated excellently by F. Murray Abraham, begins in the forests of Papua New Guinea, where tribesmen are hunting for tree kangaroos and possums, aided by a motley band of mutts in whose magical powers the men fervently believe. Off in the mist-shrouded mountains we hear a haunting form of near-music produced by the rarely seen “singing dogs of New Guinea,” which should really form a band and get in touch with a record company pronto.

The hunters believe these singing dogs are the ur-dogs, the mother of all dogs, so to speak, but this, as we shall learn, does not correspond to the latest science, which places the original wolf (from which all dogs descend) near Siberia. In the meantime, their hunting dogs race nimbly through the forest, sniffing and poking and pawing at everything in sight until a great volley of barking goes up as they surround a tree with an unfortunate possum frozen in place halfway up the sturdy trunk. The tribesmen then do the easy part: They shoot the possum with a bow-and-arrow. Without the dogs to lead them to it, and to alert them to the dangers of other animals around them, they’d never have found it.

Thus we are introduced to a well-worn but endlessly recyclable theme: Dogs are useful (vital, even) and immensely hard-working. Over the years they have functioned as guides, protectors, friends, and, by catching and herding other animals, they’ve helped put food on the table as reliably as millions of working stiffs. As a contemporary shepherd in England’s Lake District says of the Border Collie, “It’s just unbelievable what you can do with that animal.” What’s more, it’s happy to do it — and do it, and do it, and do it, pretty much until it drops.

The mystery is how dogs, including the yapping Pekinese and the Park Avenue Poodle, emerged from that aloof, predatory, proto-dog, the wolf, 15,000 years ago. This program speculates that they evolved independently — and at glaringly un-Darwinian speed — by hanging around early human settlements, looking for food and ingratiating themselves with the locals. This makes intuitive sense, since dogs are geniuses of interpretation. (“… I am quite alone / And cannot understand what people say / But like a dog must guess it by the tone,” W.H. Auden once wrote in Iceland, mentally switching species.)

However it happened, dogs proved so useful (they’re nature’s cops) that people not only kept them and bred them, but traveled with them for protection: Thus they spread across the planet just as people did. The Inuits might never have colonized the Arctic Circle without sled dogs to guide and drag them across it while also locating their meals (seals). These tawny, sometimes blue-eyed creatures, can run the equivalent of five marathons a day and are as beautiful as they are bold. They’ll even fight off polar bears. Though replete with the lush photography one expects from PBS’s “Nature” series, “Dogs” includes a lot of spooky-looking, computer-generated models of how different breeds (the Saluki, the Bloodhound) function. How they have evolved over time, how they run, how they attack, and why their senses (particularly their sense of smell, which outdoes ours by 1,000 to one), are so extraordinary. The hunter-gatherers of Papua New Guinea reverently put it down to the spirit-world, but then they don’t watch television.

The second part of this two-hour documentary will show next Sunday. It deals with modern dogs — those decadent creatures you see parading in the park and the inbred freaks displayed in competition. There are lots of cute shots, taken in a white studio setting, of the boundless variety of the canine. That there is such variety can be blamed, like most things, on the British, who grabbed five Pekinese when they plundered Beijing’s Summer Palace in 1860, and presented them to Queen Victoria upon returning home.

The vogue for dogs as toys and pets then began in earnest, as did the desire to create ever more exotic breeds. There were about 40 at the start of the Industrial Revolution; there are more than 400 now. Many, like the grotesquely bulbous bulldog, are examples of overbreeding. The original bulldog was a much fleeter, nimble-footed creature. In fact, some dogs are now so biologically bizarre that their health is permanently precarious — good news for veterinarians.

As one trainer says, “For thousands of years man and dog have had a very efficient, symbiotic working relationship, and that relationship now is in crisis. We have completely forgotten the nature of this animal, and what it was designed for.” As an example, we are offered the sight of a small but hyper-aggressive terrier in an apartment. Well, they weren’t called terriers for nothing. They were bred to kill rats in the 17th century, not sit in front of the TV and look cute. Sixty-five million Americans own dogs, 4.5 million are bitten by them each year, and 5 million dogs are put down annually because they’re uncontrollable.

As well as hunting and protecting, 21st-century dogs, like everyone else, have entered the newer sectors of the service economy. For the most part, this means keeping people company. But they also sniff out bombs, counterfeit bills, and narcotics, and are being trained to do the same with cancer. Incredibly, they can even sense a diabetic’s blood sugar running low before the symptoms manifest themselves. A future New Yorker cartoon, involving a human nurse and a canine physician, seems inevitable: “The dogtor will see you now.”

bbernhard@nysun.com