Sex with your sibling is called incest and is illegal in almost all 50 states. Sex with your sibling or other close relations, if you are a dog, is called inbreeding, and inbreeding is part of the practice of pure-breeding dogs.
Breeders are not typically mating siblings, though it is not prohibited by the American Kennel Club and is not unheard-of. Any mating within a closed gene pool of candidates will do, as far as breeders are concerned. But according to research published by a team from the University of California, Davis, and Wisdom Health Genetics in Finland, purebred dogs have, on average, a “coefficient of inbreeding” of 0.25, the same number you get when two siblings have a child. This number indicates the probability that two individuals will share two alleles from a common ancestor, like a parent or grandparent. And this number — 0.25 — is a problem.
The results of pure-breeding, on display recently at the Westminster Kennel Club Dog Show in New York, are profound. The radical morphological diversity of dog breeds today — from four-pound Malteses, white-haired and small-faced, to 170-pound Great Danes, large of body and of presence — is due to selective breeding.
So, too, are the consequences: the occurrence of several hundred health disorders related to genetics or to adherence to the standards set by breed groups that have emerged since dog pure-breeding took off in the 19th century. These include changes to anatomy so drastic that they affect reproduction (the bulldog’s head is so big that the overwhelming majority cannot be birthed naturally), respiration (the pug’s small skull leads to a constellation of abnormalities that make breathing difficult) and recreation (the German shepherd and other large-breed dogs are prone to debilitating hip dysplasia).
The U.C. Davis research, led by Danika Bannasch, a veterinary geneticist, also found that the more inbred a breed was, the more inherited disease the breed had. (Remember the number they found, 0.25? Healthy rates of genetic similarity occur with a coefficient of inbreeding below 0.05.) This finding aligns with what anyone who has taken biology already knows: When you limit the breeding population, the frequency of potentially unhealthy mutations increases, as deleterious but recessive alleles become prominent.
When we breed to a type, genetic diversity is lost. Now we have dozens of small- and large-scale studies showing the inevitable results of inbreeding with dogs: smaller litter sizes, fewer surviving newborns and even decreasing life spans. A large 2019 study found, controlling for size, that purebred dogs lived over a year less than mixed-breed dogs did. As a society, in other words, we’re trading a year of their lives for the ability to choose their shape, size and color.
Morbidity is a measure of suffering from disease, shown here as the number of non-routine vet visits for each breed, per 10,000 dog years, as observed by an insurance company.
Dogs are living examples of a paradox — the paradox of our human impulses. I know no dog people who want their dogs to live a year less than they would, statistically speaking, if they were mutts. But I know lots of people who want to purchase a purebred dog. Why is this? I think it comes down to our psychological tendencies, on one hand, and consumer mind-set, on the other.
Psychologically, we love anecdotal data and are easily persuaded by single data points. As a researcher on dog cognition for the past 20 years, I have seen this demonstrated in reaction to published and replicated research when our experiences seem to belie the results. When I describe research that finds that the guilty look of dogs is a response to their owners’ behavior, not a reflection of their understanding of their own misbehavior, the most common reaction I receive is: But my dog looks guilty only when he is guilty.
There are plenty of individual examples of long-lived purebred dogs — several of the oldest living dogs on record, north of 20 years, are purebred — so we hold on to those anecdotes, like a smoker to cigarettes because a grandmother lived until 102 clutching her Marlboros. Also contributing to our paradoxical behavior is our love for buying things, even (sometimes especially) living things. Societally, we treat dogs as commercial products, although each dog purchaser is hoping the dog will become a member of the family, not shelved with our other household objects for display.
In an era when you can get groceries and a new computer delivered to your home in an hour, I am surprised that we can’t buy puppies on Amazon (yet). But we can head online, scrolling through websites and collecting recommendations from other dog purchasers. We start to imagine the kind of dog we would like, with features we can choose. The American Kennel Club and the dog breed clubs within it are happy to tell you about the features you can expect in your new dog — friendly, good with kids, trainable. The possibility of a reliable dog product is more fun to believe in than the scholarly research that clearly demonstrates that breed type is a poor predictor of behavior. The illusion of certainty mesmerizes us.
The deluge of evidence showing both the ubiquity of inbreeding and its detrimental results is a chance for reflection. While science is steadily producing more details about exactly how inbreeding is deforming the species we claim to love, there is nothing fundamentally new here: We have known for years about the poor results for dogs. What the evidence may now be showing us, though, is the poor result for us: We are a species that is willfully damaging dogs.
This result is born not just of our obsession with breeds or our willingness to overlook the damage of inbreeding but also of our thinking about dogs as objects to be molded to our desires. We are drawn to the infantile look of big-eyed, flat-faced dogs, and as a result, we inadvertently created dogs whose eyes ulcerate and whose noses and tracheas are small and often nearly blocked. We are drawn to dogs with distinctive coats (Dalmatian: spotted; Rhodesian Ridgeback: with a characteristic line down the spine), the genes for which also lead to disorders (Dalmatian: deafness; Ridgeback: dermoid sinus, a neural tube defect).
As a species, we are so attached to the idea that we should be able to buy a dog who looks however we like — flat of face or fancy of coat — that we are willing to overlook the consequences for the species, for the breeds and often for the very sweet, exuberant pup we add to our families.
We have a chance to redeem ourselves. Right now, the American Kennel Club has no constraints on inbreeding (even as it encourages breeders to remember that “crippling or fatal” hereditary diseases may result). But I am not counting on the American Kennel Club. Instead, we could make outcrosses — the introduction of different genetic material to breeds — the norm. Research looking at dog genotypes and phenotypes has found several putative genes associated with longevity in dogs. What if we pursued robust health, instead of breed standards based on appearance, by investigating and working with those genes? If we loosen our grip on the idea that dogs are consumer objects to be designed and from whom we can demand certain behaviors, we will have a chance to meet dogs again on their own terms.