The Dog Breeds Most Attached to Humans
We're learning more and more about how ancient dogs became domesticated. However, some dog breeds clearly remain more closely related to wolves and don't look to humans for help, while others have a higher level of attachment to humans and may be less fearful and aggressive.
Analysis by Dr. Karen Shaw Becker
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STORY AT-A-GLANCE
- A new study reveals genetic changes that lowered the stress levels of ancient dogs may have played a role in domestication
- The study results show that dog breeds that remain relatively closely related to wolves (e.g., Siberian Huskies, Akitas) don’t look to humans for help as often as breeds more distantly related to wolves
- The researchers concluded that more recent dog breeds have a higher level of social attachment to humans
- An earlier study provides evidence that even wolf pups hand-raised by humans from birth don’t “get” us like domesticated dogs do
- Unlike dog puppies, even hand-raised wolf puppies don’t look to humans to help them solve problems
The wolf ancestors of today’s canine companions began their evolutionary journey toward domestication over 10,000 years ago, but not for lack of trying, scientists have yet to solve the mystery of exactly how and why the process took place.
Undeterred by their 100-years-and-counting quest, researchers remain doggedly determined to put the puzzle together. Another piece of that puzzle may have slid into place with the results of a new study titled "Identification of genes associated with human-canine communication in canine evolution," published in Scientific Reports.
The study reveals that genetic changes that lowered the stress levels of ancient dogs when they encountered humans may have played a role in domestication.
"This is the first genetic demonstration that supports the hypothesis that mutations in the stress response system initiated canine domestication," study senior author Miho Nagasawa, an animal scientist at Japan’s Azabu University, told the Scientific American.
Some Breeds Are More Trusting of Humans Than Others
The research team recruited 624 dogs and their humans to participate in their study. They divided the dogs into two groups, with one group consisting of breeds relatively closely related to wolves (e.g., Siberian Huskies and Akitas), and the other group containing breeds more distantly related to their wild cousins.
The experiment involved two behavioral tasks. The first task required the dogs to look to cues from the researchers, such as the direction of their gaze or a pointing gesture, to determine which of two bowls had a treat hidden under it. The purpose was to determine how well the dogs understood human communication signals, and it built on earlier study results that show even very young puppies understand human signals better than adult wolves raised by people.
In the current study, the researchers found no differences in performance between the two groups of dogs.
In the second task, the dogs were given a challenge they couldn’t conquer: getting into an unopenable container that contained a yummy food treat. The researchers measured how much time the dogs spent looking to them for help, which is another behavior dogs are better at than wolves.
Interestingly, during this task a significant difference emerged between the two groups. The group with the Akitas and Siberian Huskies (the "wolfier" breeds) spent less time looking to the humans for help. The researchers concluded that more recent dog breeds have a higher level of social attachment to humans.
More Recent Dog Breeds May Have Evolved Lower Stress Levels
With the behavioral tasks completed, the researchers next analyzed four genes in the dogs to look for differences that might influence their relationship with humans. Included were genes involved in the production of oxytocin (the "love hormone"), and the stress hormone cortisol.
What they found were mutations in a cortisol-producing gene that differed between the two groups of dogs, suggesting the more recent breeds had lower cortisol levels. These findings are in line with an earlier study that showed foxes selectively bred to be less fearful and aggressive around humans also had lower cortisol levels.
Since there appears to be a correlation between mutations in the cortisol-producing gene in the more recent dogs and the underdeveloped social-cognitive abilities of the wolfier dogs, the authors theorize that lower stress levels probably played a role in dog domestication. After all, becoming less distrustful of humans would be a logical first step in developing the social-cognitive skills needed to interact and communicate with them.
"Although it is not yet clear whether cortisol, a marker of stress, is actually lower in dogs than in wolves," says Nagasawa, "the fact that two genetic mutations were observed — one of which is accompanied by changes in the production of intracellular cortisol — may provide clues to how the canine tolerance and ability to adapt easily to human society was acquired."
The researchers are now involved in follow-up research to check whether cortisol levels actually differ between the two groups.
Dogs Have Evolved to Possess ‘Theory of Mind’
A 2021 Duke University study demonstrated that you can hand raise a wolf puppy, snuggle and cuddle him often, and otherwise manage him exactly as you would a domesticated pup, but little Wolfie will never quite "get" you like your dog does.
When you point and say, "go get your ball," your dog will run right to it. Wolfie? Not so much. The ability to comprehend human gestures may seem like a no-brainer, but it’s actually a complex cognitive skill that is rare among animals. Chimpanzees, our closest relative, can’t do it.
After thousands of years of domestication, it seems dogs have developed some of the same cognitive abilities as human babies. They’ve evolved to possess something called "theory of mind" mental skills that give them the ability to infer what humans think and feel in certain situations.
Dog Pups Win Big in the ‘Find the Treat’ Test
The Duke study involved 44 dog and 37 wolf puppies between 5 and 18 weeks of age. The wolf pups were housed at the Wildlife Science Center in Minnesota and were genetically tested to ensure they weren’t wolf-dog hybrids. They were raised with lots of human interaction: they were hand-fed, slept in their caretakers’ beds at night, and received round-the-clock human attention from just days after birth.
In contrast, the dog puppies, who were from Canine Companions for Independence, lived with their mother and littermates and had less human contact.
In one test, a treat was hidden in one of two bowls, and each dog or wolf pup was given a clue by a researcher to help them find the food. Clues included pointing and gazing in the direction the treat was hidden and placing a small wooden block beside the right bowl — a gesture the puppies had never seen before — to indicate where the treat was hidden. According to a Duke Today news release:
"The results were striking. Even with no specific training, dog puppies as young as eight weeks old understood where to go, and were twice as likely to get it right as wolf puppies the same age who had spent far more time around people.
Seventeen out of 31 dog puppies consistently went to the right bowl. In contrast, none out of 26 human-reared wolf pups did better than a random guess. Control trials showed the puppies weren't simply sniffing out the food.
Even more impressive, many of the dog puppies got it right on their first trial. Absolutely no training necessary. They just get it."
Wolf Pups Lack People-Reading Skills, Fear Strangers
It’s important to note that the study wasn’t about which species is "smarter," and in fact, all the pups performed equally in tests of other cognitive abilities such as memory and motor impulse control. The difference became obvious only in the realm of people-reading skills.
"There's lots of different ways to be smart," said doctoral student and lead study author Hannah Salomons. "Animals evolve cognition in a way that will help them succeed in whatever environment they're living in."
Other tests showed that the dog pups were also 30 times more likely than wolf pups to approach a stranger.
"With the dog puppies we worked with, if you walk into their enclosure they gather around and want to climb on you and lick your face, whereas most of the wolf puppies run to the corner and hide," Salomons said.
Domestication Is Responsible for the ‘Social Genius’ of Dogs
In a test in which treats were placed inside a sealed container so the puppies couldn’t access them, like the "wolfie" dog breeds in the Japanese study, the wolf pups mostly tried to solve the problem on their own, while the dog puppies spent more time asking for help from nearby humans through direct eye contact, as if to say, "I’m stuck, can you fix this?"
Brian Hare, senior study author and professor of evolutionary anthropology at Duke believes the research provides some of the strongest evidence to date to support the "domestication hypothesis." From the news release:
"Somewhere between 12,000 and 40,000 years ago, long before dogs learned to fetch, they shared an ancestor with wolves. How such feared and loathed predators transformed into man's best friend is still a bit of a mystery.
But one theory is that, when humans and wolves first met, only the friendliest wolves would have been tolerated and gotten close enough to scavenge on the human's leftovers instead of running away. Whereas the shyer, surlier wolves might go hungry, the friendlier ones would survive and pass on the genes that made them less fearful or aggressive toward humans.
The theory is that this continued generation after generation, until the wolf's descendants became masters at gauging the intentions of people they interact with by deciphering their gestures and social cues."
According to Hare, "This study really solidifies the evidence that the social genius of dogs is a product of domestication." He believes it’s this ability that makes dogs born prepared to be great service animals. Like human babies, dog puppies intuitively understand that when humans point, they’re trying to communicate something. Wolf puppies don’t possess this understanding.
"We think it indicates a really important element of social cognition, which is that others are trying to help you," Hare said.
And according to Salomons, "Dogs are born with this innate ability to understand that we're communicating with them and we're trying to cooperate with them."
