As cameras rolled, the young researchers stretched forward on their bellies toward the two wolves, raw meat in hand.

“Puppy, look!” Gitanjali Gnanadesikan and Daniel Horschler called in unison, holding out chunks of fresh hamburger.

The six-week-old predators, all floppy tails and ears, padded around the small enclosure in search of the meat, interested in the behavioral test disguised as a game. They wiggled to the chirps and calls of the humans who’ve nurtured them. But not for long.

Researchers like Gnanadesikan and Horschler know that wolf puppies harbor an ancient wariness of humans beneath the surface, even if they’ve been hand-raised and bottle-fed. The sharp shift from friendly pup to fearful wolf is a phenomenon that has drawn teams from the University of Arizona and Duke University to the Wildlife Science Center in Anoka County, where researchers are spending the summer studying how wolves think.

Scientists want to know what happened to dogs thousands of years ago during domestication, and what that might reveal about human evolution. Since 2014, researchers have been probing these questions among the captive wolves at the Wildlife Science Center, an internationally known education and research facility west of Stacy where thousands of students venture each year for science programs.

Two small teams from Duke and Arizona are making a concerted push to gather more data in the hope that they’ll soon have a sample large enough to publish some of their findings, no small feat. Wolf puppies can be tough to come by in a research setting.

“It’s the biggest summer on this kind of work that we’ve ever had,” said Evan MacLean, director of the Arizona Canine Cognition Center at the University of Arizona.

For nearly two months, researchers have been working with adult wolves and pups at the Science Center, using simple problem-solving games with food rewards. The tests often involve social cues from humans, such as pointing to food, and then seeing how wolves respond to “cooperative communication.”

The researchers also have been collecting biological samples — saliva, urine, feces, blood — to track hormonal changes during development. The scientists wonder if some biological change may help explain the shift when wolves lose their willingness to interact with people.

Such research, they say, could reveal more about how dogs evolved.

From friendly to fearful

Questions about dog and wolf differences have been studied for years, but sample sizes for wolves are typically small and sometimes offer conflicting findings, MacLean said.

That’s why it’s especially useful to study wolves and dogs during development, from puppyhood to adulthood, paying attention to when differences between the two emerge.

Scientists know that dogs seem to understand human gestures like pointing, grasping that people are trying to communicate something helpful to them. Not so with most animal species, including chimpanzees, MacLean said.

“Dogs seem sort of predisposed to treat humans almost as if we’re members of the same species,” he said.

Take, for instance, a dog trying to retrieve food from a box with a lid. At first, Fido manages to do so. Then the problem gets trickier: Can the dog get food if the lid is locked?

When stumped, dogs seem to look to humans to solicit help. Wolves, meanwhile, “will basically persist on their own,” MacLean said.

Scientists suspect dogs have taken many of the skills that wolves use to cooperate and communicate with each other and adapted those skills to interact with humans and perhaps other animals.

But in all this canine talk, human cognition is never far from view. Researchers think some of the changes that unfolded in dog domestication bear similarities to changes in human evolution, especially when it comes to cooperative gestures like pointing or following another person’s gaze.

These basic skills for communicating help set the stage for things like language acquisition, MacLean said.

“We’re interested in these questions because we think there’s actually something very special about our own species,” he said.

Bonding with wolves

For wolf puppies, there’s a narrow window to do this kind of testing before the fear sets in.

Wolf expert Peggy Callahan, executive director at the Wildlife Science Center, knows this shift all too well, having worked with wolves for decades and hand-raised her share of litters.

“It’s literally overnight,” Callahan said. “Normally they run up and are greeting everybody that comes in the bedroom, and then one day you open the door and they run and hide in the closet.”

Even with the most dog-like wolf puppies, she said, “You can’t love the wolf out of them.”

The Duke and Arizona researchers have been living at the center since May. They plan to compare this summer’s findings with the deep cache of dog data already kept at both universities.

The team from Duke has been working primarily with adult wolves, including some that researchers tested as puppies in years past.

“There’s really not anything that’s been done with this big of a sample size” over time, said James Brooks, a recent Duke grad involved with the project.

Meanwhile, the Arizona team has been studying 12 wolf puppies born at the center this spring. While the two-person team has performed similar behavioral tests with dog puppies, it didn’t take long to realize that some tests needed tweaking to suit young wolves.

“The wolves really react much better to humans when they’re sitting or lying down on the ground,” said Gnanadesikan.

On a recent morning, Gnanadesikan and Horschler, both Arizona graduate students, showed the wolf puppies bright red hamburger meat while crouching nearly on their bellies in a cabin at the center.

The pair leaned forward to show two puppies the food before setting it on X’s chalked before them on the concrete floor. During some trials, one person sat facing the puppies and looked at the meat, while the other sat facing away, the meat and wolves behind them.

They wanted to see whether the puppies seemed to follow the human’s gaze to help find the food, or if they seemed more comfortable searching without a person facing them.

Gnanadesikan and Horschler have spent weeks bonding with the pups. They call each of them by name, observing their behavior by day and taking turns sleeping with them outside by night.

But soon, they know the ancient fear will kick in. And in just a few short weeks, the puppies likely will begin to treat the humans who’ve cared for them less like bedfellows and more like strangers.