“Service animals” have been much in the news these past few years. During one recent summer, stories proliferated about problems on airplanes as passengers were bringing all manner of wildlife on board under the rubric of “emotional support.” Suddenly there were service pigs in the friendly skies, and service ducks, as well as the occasional service turkey, penguin, peacock, and, yes, even a service kangaroo. It was hard to escape the conclusion—later corroborated by reports that shady businesses were selling fraudulent service-animal authorization letters—that some people wanted to avoid airline shipping fees (or were unwilling to entrust their animals to the cargo hold).

This spate of stories was especially regrettable because such cynicism obscures, and can even appear to lessen, the importance of the original service animal: the seeing-eye dog. We have all heard of these extraordinary creatures, and have probably seen a few in action, but I wonder if most of us have ever considered how these animals, and the work they do, contribute to our understanding of the human person. In their unassuming way, they reveal to us—if we are prepared to look for it—the true nature of our shared humanity. Seeing-eye dogs are not only for the seeing-impaired. They can help whoever thinks about them in a serious way to become aware of things not quite appreciated before.

There are many animals, of course, which serve humankind in some way. Horses, mules, and oxen have borne man and his burdens for millennia. Cows and goats have given him milk to drink. Sheep have given him wool for clothing. Antebellum ladies wore hoop skirts flared out with crescent-shaped whalebones. Hog bristles make excellent hairbrushes. And many modern-day apartment-dwellers are cheered by the company of turtles, goldfish, cats, finches, and canaries.

How is a seeing-eye dog different from other dogs and other kinds of service animals?

I had never really thought of this question until, on a recent trans-Pacific flight, I watched a remarkable documentary. Pick of the Litter is an award-winning 2018 film about Labrador Retriever siblings going through a grueling selection process to determine which, if any, will become Guide Dogs for the Blind. A seeing-eye dog, I later reflected, is not like other animals whose bodies we harness to do work for us. Guide dogs do not merely serve man. They love him. Camels must be whipped into doing our bidding, and falcons tethered to stay on the wrist, but a seeing-eye dog, once properly trained, wants to help, wants to keep his/her owner out of harm’s way. A seeing-eye dog forms a relationship with a human being that is utterly unlike the way in which we interact with any other animal. Somehow, the seeing-eye dog affirms our humanity at the deepest level, a reminder that giving of oneself is the meaning of our human existence.

Indeed, a seeing-eye dog’s own existence is rooted in sacrifice, both human and canine. Potential seeing-eye dogs are sent out as puppies to people who initially raise them and teach them how to live among humankind. Dogs are a different species, after all—though many dogs I have known apparently had long forgotten they were not part of the human family—so they must be taught how to take on our ways as much as they can.

Once socialized and housebroken, dogs that show character potential—confidence, work-ethic, friendly disposition—are returned to Guide Dogs for the Blind facilities for intensive training in how to lead visually-impaired people through the world. The entire process is riven with emotional and physical pain. The trainers and dogs wear themselves out in round after round of trials. Legs ache, patience frays, blisters bubble, break, and bleed. And, despite their best intentions—and despite knowing that the inevitable day of separation will come—foster-owners love their dogs, go through thick and thin with them as they teach them and overcome failures, and cry when it is time for the dogs to leave. In a strangely beautiful way, the eyesight that is lacking in a stranger is, somehow, supplied by the suffering of other people—and through the medium of this goofy, gangly, intensely loyal animal that is not for nothing called “man’s best friend.”

In the end, even most of this hard work must be sacrificed, as only the best of these canines will make the cut. Most of them, of course, are just regular dogs, born to gnaw on sticks and chase squirrels in the backyard, to beg for table scraps and sigh during belly rubs—in short, to join a human family in the usual doggy way. But some dogs complete the training and, in the process, are utterly transformed. The clumsy puppy, over time, gives way to an animal that can only be described as noble. The hard work and sacrifice of countless people, and of the dog itself, temper the raw material into a new thing, a gift to the blind person whose life, in all likelihood, will also be transformed thereby.

This is not hyperbole. Seeing-eye dogs daily perform miraculous feats of protection. Morris Frank and Blake Clark’s 1957 book First Lady of the Seeing Eye details a whole bevy of ways in which Frank’s seeing-eye dog, Buddy, guided him safely up and down stairs, into and out of elevators, and across busy New York City streets. A seeing-eye dog is like a guardian angel with a rambunctious tail. Pick of the Litter shows all of this in full color. At stoplights and at key moments during every human activity, the dogs look around at the world as they also watch their owners intensely. The dogs know us, and want to keep knowing us better. This is how they guide us. A seeing-eye dog does not just help the blind cross at the crosswalk. In some sense, and after their own fashion, they have entered into our interior selves and formed a communion with us as fellow creatures. As one recipient of a seeing-eye dog puts it in the film, “It’s not easy to be visually impaired. A cane can help, but it’s not as great as a fuzzy face and a wet nose.” Grace completes nature. And the seeing-eye dog’s nature is, in a mysterious way, a conduit for the grace of giving.

When people cynically game the system to bring various animals onto airplanes, they are, sadly, acting out the script of our modern age: Use one another, gain the advantage, do whatever you need to do to survive. But when people give up time, money, sweat, and heart to train dogs—often with but small chance of success—so that someone else’s life might be immeasurably made better, they are reading from a different text, one written deep in the fabric of who we really are. It is, surely, much more than a coincidence that one animal, among all the others, understands this about us, and teaches us while we are training them.