Which dog breed is the strongest and healthiest of them all? Is it the Border Collie, with its elegant coat and affectionate personality? Or is it the English Bulldog with its burly frame and gentle disposition?

To tell you the truth, it’s neither. Nor is it any other dog breed you’re familiar with. In fact, purebred dogs are the unhealthiest variety of canine because of the way they’ve been bred: We bred them to emphasize attributes that we find cute or useful, while we ignored the attributes that keep dogs healthy and fit for a life in our natural world.

Humans began breeding dogs 14,000-17,000 years ago, but it’s only been in last few centuries that we developed most of the dog breeds we know today. And now, despite all belonging to the same species, Canis lupus familiaris, dogs come in all shapes, sizes, and colors.

Along with their variety of visual characteristics, different purebred dog breeds harbor a host of health issues. Half of Cavalier King Charles Spaniels, for instance, develop heart disease by the time they’re five years old. Additionally, due to their large size, Great Danes often suffer from hip problems and arthritis, and their hearts aren’t strong enough to pump their blood through their bodies.

Pugs and other breeds with flat noses have shortened nasal passages and a compressed upper respiratory system, which makes it hard for them to breathe. On top of that, they sometimes experience an odd problem called “reverse sneezing.” The dog’s throat muscles spasm, causing it to gasp loudly, its eyes to bulge, and its windpipe to narrow, making it even more difficult for the poor dog to breathe.

Unfortunately, there’s an epidemic of disease among our dogs. How did we get to this point?

Several hundred years ago, we began selectively breeding dogs to develop traits that could help us in the home and in the fields. If we found a dog that looked like it had potential as a house pet or a working dog, we bred it with similar dogs until the traits we wanted started to show up consistently in their offspring. Once we found a dog that looked and acted the way we wanted, we decided to call it by a certain name (what we now call breeds), and we continued to only breed it with dogs of the same breed so those traits would stick.

Where do breeders find so many dogs with similar traits to pair up? Start by thinking about whose traits are most similar to yours. Your family, right? To maintain a genetically pure lineage, breeders often breed dogs with their family members, so that together, they will produce genetically similar offspring. Breeders continue this practice today to maintain the purest breeds that we all know and love.

dangers dog breeding
Citrus greening disease has spread rapidly across the southeastern United States because orange trees lack lack of genetic diversity.

Meanwhile, nature’s strength comes from its genetic diversity. In a forest that is not genetically diverse, for instance, a disease that exploits a genetic weakness in one tree will probably find the same weakness in all the trees and kill off the whole forest. (This is what is happening to Florida’s fruit trees.) But if the forest is genetically diverse, a disease that affects one tree likely won’t have an effect on most of the forest, leaving behind a healthy and prosperous population.

And unfortunately, it’s difficult to create diversity out of a population that is not diverse to begin with. For example, instead of a forest, think of a school of fish. Let’s say one fish in that school carries a genetic mutation that causes it to grow small fins. Smaller fins are a weakness for this fish, so if it knew what was best for its offspring, it would mate with a fish with normal fins. Doing so would reduce the chance that this weakling will produce a new generation of weaklings. Rather, this fish’s progeny might inherit normal fin traits from its other parent.

Now, if this small-finned fish is in a genetically diverse school, it will have no trouble finding a mate with normal fins. But if that school is not diverse, that fish is bound to mate with another fish with the same problem, and together, they will pass this harmful trait down to their offspring. Ashkenazi Jews suffer from this problem. Today’s Ashkenazi population originated from a “genetic bottleneck” of just 350 closely related individuals about 700 years ago, and ever since, the harmful traits they carried, such as the ones that cause Tay-Sach’s disease, have been passed on from one generation to the next.

The same principle applies everywhere in nature: in bacteria, flowers, and you guessed it, dogs.

Because we’ve interbred dogs for so long, the harmful genetic mutations that would normally get washed out in the gene pool have perpetuated from one generation to the next in a process called “genetic drift.” In a normal population, such as flowers in a natural prairie, all of the individuals in that population would mate randomly, producing offspring with a solid mix of traits from the whole population. But since domestic dogs don’t mate randomly, and instead mate almost exclusively with dogs that are very similar to them, the population has “drifted” away from its wild ancestors. And we choose to perpetuate these disease traits because they piggyback on traits that we find cute, majestic, or useful in our culture. Meanwhile, domestic dogs have drifted away from their most closely-related cousins, the wolf, losing many traits, such as assertiveness and self-reliance, that make them fit for the natural word.

dangers dog breeding
Aww, look at that face!

Are there any dogs out there that are healthy? Yes. They’re the ones we call mixed-breeds, or mutts. These dogs, which are mixes of two or more breeds, are closer their wild ancestors, genetically speaking, than their pure breed cousins. This means they are more fit to survive in nature. Mutts have what scientists call “hybrid vigor,” and while their survival skills may never be tested in nature, they’re more likely to live longer, healthier lives in your home.

If you are thinking about getting a dog, consider where the dog is coming from. The choice to spend thousands of dollars on a purebred dog from a breeder supports an industry that harms dogs by making them prone to disease and disability. Instead go to a shelter, and you’ll have a better chance of finding mixed-breed dogs that will live longer, healthier lives, and who really need loving homes.


  • Ben Marcus

    Ben Marcus is a public relations specialist at CG Life and a co-editor-in-chief of Science Unsealed. He received his Ph.D. in neuroscience from the University of Chicago.

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