Some wolf puppies are unexpectedly willing to play fetch, according to scientists who saw young wolves retrieve a ball thrown by a stranger and bring it back at that person's urging.

This behavior wouldn't be surprising in a dog. But wolves are thought to be less responsive to human cues because they haven't gone through thousands of years of domestication.

Exactly how dogs emerged from a now-extinct population of ancient wolves is a mystery. Wolves are large, dangerous carnivores, and yet they were the first animals that humans tamed. More than 15,000 years ago, when humans were still hunter gatherers, this large predator somehow began cozying up to people, eventually becoming their "best friend."

To try to get clues about how that happened, scientists such as Christina Hansen Wheat of Stockholm University in Sweden have been studying the differences between dogs and modern wolves. As part of her work, she raised litters of wolf puppies, feeding them and acclimating them to her presence but not playing with them or training them.

At the age of 8 weeks, the wolf pups were put through a series of standard behavior tests that were administered by a person the wolves had never met.

This set of tests is normally used by dog breeders, says Hansen Wheat, to assess how their puppies act in social situations. "The fetching test just happened to be part of this test battery. It wasn't something we were targeting at all," she says.

The person conducting the test threw a tennis ball and urged the wolf puppy to bring it back. Two litters of puppies utterly failed to do this, surprising the scientists not at all.

"There's some hypotheses out there that the ability to understand human social cues is a unique dog trait, a trait that arose after domestication had been initiated," Hansen Wheat explains, so fetching on command is not a behavior expected in wolves.

But then a third litter went through the tests. And as she watched through a window, one of the wolf puppies went for the ball and returned it to the tester, according to a report in the journal iScience.

"When I saw the first puppy fetch — I still get goosebumps when I talk about this — it was such a surprise," Hansen Wheat says. "It wasn't just one puppy, it was actually three of them. That was very exciting."

Because three of the 13 tested wolf puppies spontaneously did this, a willingness to fetch might not be a dog trait, she says. Instead, it might be a wolf trait that existed in the ancestral wolf populations.

"It might have been something that we have tried to select upon during early domestication," Hansen Wheat says. "Wolf puppies doing this during early stages of domestication might have had a selective advantage, if they managed to establish a connection to our forefathers."

She notes that researchers who work with wolves typically have few animals to test. That means scientists simply might not have enough wolves to detect rare traits, making it hard to see variations as they attempt to compare wolves with dogs.

"I think it will surprise dog owners as much as it surprised me that wolves actually can fetch a ball, or retrieve a ball for a person," she says.

Evan MacLean, who studies dog cognition at the University of Arizona, says this is an interesting observation that no one has made before.

"To my knowledge, this is actually the first test ever to look at whether wolves do something like this," he says.

Watching the video, MacLean sees two discrete behaviors: first, chasing the ball and biting it, and then later coming back to the person while carrying the ball. To him, it doesn't appear to be exactly the same kind of goal-oriented game of "fetch" that a dog would play with its owner.

"But I think it's an intriguing observation," he says. "I think it opens up a series of interesting questions and other studies you could do to try to look at this in a more controlled and systematic way."

Would the wolves behave this way if there were distractions in the room, for example, or if the ball were thrown by a machine instead of a person?

There's no agreement on how dog domestication happened — whether some brave wolves started hanging around human camps to get scraps or whether humans actively kidnapped wolf puppies to raise them.

In recent times, MacLean notes, wolves have been extensively hunted by humans, so today's wolves might be more skittish around people than past wolf populations were. "It's possible that the modern populations are quite different than the population that actually gave rise to dogs," he says.

Dogs do seem to be sensitive to human gestures, such as pointing, in ways that other species are not, including our closest relatives, chimpanzees.

"Dogs have become special in that regard," MacLean says, "and some people, myself included, have made claims that maybe this is something really unusual about dogs, and something that changed during dog domestication."

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