In a rare candid moment, researchers have observed a captive-bred wolf puppy spontaneously playing fetch with a human in what could help illuminate why some dogs were domesticated and others not over the course of human-canine evolution.

The canine ability to interpret human social and communication cues was thought to arise in dogs only after human domestication some 15,000 years ago. Now, it appears this unique ability also exists in wolves, according to research published in the journal iScience.

"When I saw the first wolf puppy retrieving the ball I literally got goose bumps," said researcher Christina Hansen Wheat, of Stockholm University in Sweden, in a statement. "It was so unexpected, and I immediately knew that this meant that if variation in human-directed play behavior exists in wolves, this behavior could have been a potential target for early selective pressures exerted during dog domestication."

Hansen has been hand-raising wolves and dogs under identical conditions for the last three years in an effort to collect data that might explain how dogs became man’s best friend. Her team observed the behaviors of 13 wolf puppies from three different litters in order to study how domestication affects behavior. Each animal was raised from the age of 10 days and put through a variety of behavioral tests, one of which included a stranger throwing a tennis ball across the room and encouraging an untrained pup to bring it back. Puppies were scored on a scale of 1 to 5, with 1 being no interest shown in the ball and 5 indicating that the animal responds and retrieves.

Three 8-week-old puppies showed interest in the ball and returned it to the stranger upon encouragement. Hansen says this finding comes as a surprise. The first two litters of wolf puppies showed no interest in the balls, whereas some in the third litter not only went after it but brought it back when encouraged by an unfamiliar person.

Hansen notes that although watching a wolf pup spontaneously play fetch is surprising, it makes sense a wolf pup would connect with a person.

"Wolf puppies showing human-directed behavior could have had a selective advantage in early stages of dog domestication," said Hansen, a finding that could have “significant implications” for understanding the genetic foundation of animal behavior in response to human cues.

Of course, the wolf pups are raised by humans at 10 days old, which begs the question of whether they truly replicate wolf behaviors in the wild. Domestication has been shown to alter phenotypes, observable characteristics in an individual animal, through genetic mutations and variations. Throughout the course of history, humans likely domesticated dogs that had desirable traits just like we saw in the farm fox project, where Russian breeders chose foxes that were more docile, tame, and better-suited for pet life.

Dogs today are bred for highly specific reasons to exhibit different physical and mental traits – some are hypoallergenic, while others are extremely good workers. The researchers say they will continue with their dataset to learn more about how dogs evolved alongside humans.