Are you a fan of big, liquid “puppy” eyes that gaze at you soulfully, begging for, well, just about anything?
Of course you are, but don’t blame your pup. Study finds humans contribute to those irresistibly sweet eyes; in fact, we bred those sad eyes into today’s domesticated dogs starting around 33,000 years ago. The findings suggest that humans contributed to dogs’ ability to form facial expressions over thousands of years of selective breeding.
“Dogs are unique from other mammals in their reciprocal bond with humans, which can be demonstrated through mutual gaze, something we don’t see between humans and other domesticated mammals, such as horses or cats,” she said. lead author Anne Burrows, professor in the department. of physical therapy at Duquesne University’s College of Health Sciences Ranges in Pittsburgh, in a statement.
“Throughout the domestication process, humans may have selectively bred dogs based on facial expressions that were similar to their own,” Burrows said.
It turns out that dogs, compared to their genetic cousin the wolf, have more “fast-twitch” facial muscles, Burrows said. That allows the dogs to more closely mimic our expressions, or at least look at us in a way that melts our hearts.
“Over time, dog muscles may have evolved to become ‘faster,’ further benefiting dog-human communication,” Burrows said.
Fast twitch fibers vs. slow
Fast-twitch fibers are found in muscles throughout the body, allowing us to make sudden, more powerful movements, like jumping off a starting block in a race. However, fast-twitch muscles tire quickly, so we can’t sustain that intensity for very long.
Just as their name implies, slow-twitch muscle fibers work in a more even and leisurely manner, such as allowing a runner to run long marathons where the energy needs to last.
The study, presented Tuesday at the American Anatomy Association annual meeting in Philadelphia, examined fibers in facial muscle samples from wolves and domesticated dogs.
The results showed that wolves have a lower percentage of fast-twitch than slow-twitch fibers compared to today’s domesticated dogs. Having slow-twitch muscles around the eyes and face would be helpful to wolves while howling, the researchers said, while having faster-twitch muscles would help dogs get their owners’ attention with short, quick barks and expressions. more varied.
“These differences suggest that having faster muscle fibers contributes to a dog’s ability to communicate effectively with people,” Burrows said.
Wolves also lack another ability that most dogs have, according to an earlier 2019 study by Burrows and his team. That study found that dogs have a muscle called the levator anguli oculi medialis, which can raise the inner “eyebrow,” making the eye look larger and more baby-like. A 2013 study found that dogs that do that are often more likely to be adopted.
“This movement of the eyebrows creates the ‘puppy dog eyes’ expression, which resembles the facial expressions we humans make when we are sad, making them irresistible and resulting in a nurturing response from humans,” said co-author Madisen Omstead. , laboratory director of the School of Health of Ranges. Department of physiotherapy sciences.
“We also know we’re still unconsciously selecting for these characteristics in dogs,” Omstead said, pointing to a 2013 study that showed dogs using those expressions more often “were relocated more quickly than less expressive dogs, reinforcing this.” kind of evolutionary scenario even today.”
Another muscle, called the retractor anguli oculi lateralis muscle, pulls the outer corners of the eyelids toward the ears, effectively producing what we humans would call an “eye smile.” The 2019 study found that while wolves had some of this muscle fiber, most domesticated dogs had more developed muscle and used it frequently.
The exception to that rule is the Siberian husky, which is more closely related to wolves than many other breeds, the researchers said.
If the muscles that allow your dog to smile and look sweet aren’t enough, looking into the eyes of our “best friends” also seems to trigger an “oxytocin feedback loop” between humans and our dogs, much like the one that exists between human mothers and their babies, according to the researchers.
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