Most pups love to play, whether it’s chasing balls, engaging in a game of tug-of-war, or tearing that squeaky toy to smithereens. For humans, playing with a dog usually lifts our spirits; in fact, science shows that dog owners laugh more often than cat owners.
So it’s no surprise that dogs’ willingness to play with us may have been a key factor in their domestication, and may have guided our subsequent efforts to breed canines for specific functions, according to a new study published today in the journal Biology Letters.
While researchers continue to debate when, where, and how dogs were first domesticated, most agree that a wolf ancestor likely initiated the first contact with humans.
This as-yet-unidentified species of wolf likely began to hang around human settlements in Germany or Siberia between 20,000 and 40,000 years ago, snagging garbage and leftovers. The less-fearful individuals in the pack likely lost their wolfish demeanors, such as skittishness and shyness, and evolved over time into the happy, friendly, and loyal domestic dogs that warm our hearts and hearths.
In the new study, the scientists investigated if more curious and fun-loving wolves carried these traits into the new species of domestic dog, and if people intentionally bred dogs with those characteristics. Previous research, for instance, has found that some wolf puppies know intrinsically how to play ball with people.
“A dog’s willingness to play with us likely has been important to us throughout dog domestication,” says study leader Niclas Kolm, an evolutionary biologist at Stockholm University in Sweden. (Read how dogs are even more like us than we thought.)
Indeed, after analyzing the evolutionary relationships between modern dog breeds, the team found their most common ancestor, an animal akin to a present-day basenji (a type of African herding dog), would have played with people—albeit it with some encouragement.
They also found that herding dogs, such as Hungarian vizslas and Australian shepherds, were, “by far, the most playful,” engaging quickly and actively in games, Kolm says.
“It makes practical sense: If a dog is interested in playing with you, it’s much easier to train as well,” he says, adding that herding dogs need to have strong bonds with their owners to be effective, and that frequent play can strengthen such relationships.
Nearly all juvenile mammals engage in play, typically with others of the same species. They do so for physical, social, and cognitive development, and to practice skills, such as hunting, that are vital in adulthood.
Once they’ve grown up, animals rarely play, simply because they must focus on finding territories, food, and mates. Nor do they often play with animals outside their own kind.
But dogs seem to bring out the jovial nature of many species, from humans to turtles to chickens—interactions that are well documented on YouTube. Dogs and horses, which have been domesticated alongside one another on farms for centuries, also play together and share similar behaviors, such as bowing to each other.
To dig deeper into the roots of playful pups, Kolm and his colleagues investigated how human-directed play behavior evolved in 132 modern American Kennel Club breeds. These breeds are grouped by their various functions, such as herding, hunting, guarding, companionship, working (such as pulling sleds), and sporting (such as retrieving quarry). The researchers entered genetic data from the breeds into an evolutionary computer model that predicted which breed had playful traits.
The team then plugged in data collected by the Swedish Kennel Club, which analyzed the personalities and play behavior of more than 89,000 dogs from these 132 breeds between 1997 and 2013. The Swedish Kennel Club researchers assessed a dog’s willingness to play tug-of-war with an unknown person: Dogs that readily and actively participated in this game were categorized as highly playful. (Why are dogs so friendly? Science finally has an answer.)
While the results revealed herding and sporting breeds were most likely to play, toy breeds, such as pugs and papillons, were least likely. “They’re designed to be small and carried around,” Kolm says. “Playing with you isn’t important to them.”
Kolm was more surprised to find that terrier breeds, such as the Staffordshire—originally bred to be fighting dogs—are very playful, perhaps, he speculates, because they’re bred to respond to human instruction—including invitations to play.
Old dog, old tricks
Most intriguing, however, was that the basenji, the African hunting dog, was also playful, though not at a high level. The basenji is likely the oldest domesticated breed, dating to at least the 18th century. But researchers believe basenji-like dogs have been around since at least 6,000 B.C., based on Libyan cave paintings depicting such canines on a hunt.
It's impossible to know if today's basenjis behave similarly to those early dogs. But the combination of the breed’s ancient history and its playfulness strengthens the study’s finding that people have been breeding dogs in part for their sense of fun for a very long time, the study authors say. (Learn why “puppy dog eyes” evolved.)
“It’s a nice advance in the study of play,” says Gordon Burghardt, a comparative ethologist and animal-play expert at the University of Tennessee in Knoxville.
Marc Bekoff, an emeritus professor of ecology and evolutionary biology at the University of Colorado in Boulder, says the Swedish team is “likely correct in suggesting that play with humans was important in the early domestication of dogs.”
“Humans could have then directly selected for that trait,” creating dogs that were more or less playful, Bekoff, who wasn’t involved in the research, said by email.
One mystery the study doesn’t shed light on is those wolves that led to today’s fun-loving Fidos, leaving a future topic of study into the origins of our canine best friends.