Several different dog breeds on the seashore and in the waves.

Swimming is for the dogs: research shows that dog breed does not predict behaviour, such as an eagerness for a doggy paddle.Credit: Kay MacCoubrey/Getty

Dog enthusiasts have long assumed that a dog’s breed shapes its temperament. But a sweeping study comparing the behaviour and ancestry of more than 18,000 dogs finds that although ancestry does affect behaviour, breed has much less to do with a dog’s personality than is generally supposed1.

“When you adopt a dog based on its breed, you’re getting a dog that looks a certain way,” says co-author Elinor Karlsson, a computational biologist at the University of Massachusetts in Worcester. “But as far as behaviour goes, it’s kind of luck of the draw.”

Form over function

That’s partly because breeds are something of a modern invention. Humans have been shaping how dogs look and behave since domestic dogs first evolved from wolves more than 10,000 years ago. But for most of that time, these efforts were focused on dogs’ working ability — how well they herded livestock, guarded against danger or pulled sledges, for example.

Breeds as we think of them today — distinctive canines such as beagles, pugs and Labradors — are a by-product of more recent evolutionary meddling. Starting around 200 years ago, dog enthusiasts in Victorian England began inventing breeds by actively selecting for canine traits that they found aesthetically pleasing.

This experimentation created today’s breeds. Contemporary purebred dogs are defined by their looks, but breed is also thought to influence temperament. The American Kennel Club, for instance, describes pugs as “mischievous” and border collies as “affectionate”.

But, as Karlsson points out, “anyone who’s owned eight dogs from the same breed will tell you all about their different personalities”. Wanting to get a better sense of how breed influences behaviour, Karlsson and her colleagues surveyed thousands of dog owners about their pets’ backgrounds and activities, ranging from whether they had a propensity to eat grass to how likely they were to chase toys. The researchers then sequenced the DNA of a subsection of the survey dogs to see whether ancestry could be linked to behaviour.

The team found that some traits were more common in certain breeds. For example, compared with a random dog, German shepherds were more easily directed; beagles, not so much. And the authors’ genetic studies revealed that mixed-breed dogs with a particular ancestry were more likely to act in specific ways. Mutts with St Bernard ancestry, for instance, were more affectionate, whereas mutts descended from Chesapeake Bay retrievers had a penchant for wrecking doors.

Photo of Sandy, one of the mixed-breed dogs featured in the study for this story.

Among the mutts who contributed data to the new study was Sandy, whose heritage includes Australian cattle dog (21.4%) and collie (8.6%).Credit: Angela Lek

But, on average, breed explained only around 9% of the variation in how a dog behaved, a number “much smaller than most people, including me, would have expected,” says Karlsson. Particularly low was the connection between breed and how likely a dog was to display aggressive behaviour, which could have implications for how society treats “dangerous” dog breeds, says Evan MacLean, a comparative psychologist at the University of Arizona in Tucson who was not involved in the study.

“We talk about breeds like they’re categorically different,” he says. “But in reality, that’s not the case.”

Genetic analysis revealed 11 regions of the genome that are linked to specific behaviours. A tendency to howl, for example, was associated with a region near two genes whose human analogues are involved in speech. The most significant link was between a region of the genome that in humans is involved in cognitive performance — but in dogs increased the likelihood of getting stuck behind objects.

These genetic traits have been around for much longer than breeds have existed, says Kelsey Witt, a population geneticist at Brown University in Providence, Rhode Island. “At first glance, it seems surprising that breed isn’t a good predictor” of behaviour, she says. “But when you think about how recent breeds are, it makes sense.”