Humans have bred dogs to have puppy eyes

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Of course you are, but don’t blame your pup. A new study finds that humans are the culprit behind these irresistibly cute peepers — in fact, we bred those sad eyes into today’s domesticated dogs, starting around 33,000 years ago.

“Dogs are unique from other mammals in their mutual attachment to humans, which can be demonstrated through mutual gaze, something we do not observe between humans and other domesticated mammals such as horses or cats,” said senior author Anne Burrows, a professor in the Department of Medicine Physiotherapy at Duquesne University’s Rangos School of Health Sciences 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 have more “fast-twitch” facial muscles compared to their genetic cousin, the wolf, Burrows said. This allows dogs to more closely mimic our facial expressions — or at least look at us in a way that melts our hearts.

“Over time, canine muscles may have evolved to become ‘faster,’ further facilitating communication between dogs and humans,” Burrows said.

Fast vs. slow twitch fibers

Fast-twitch fibers are found in muscles throughout the body and allow us to make sudden, more powerful movements, such as walking. B. breaking out of a starting block in a race. However, fast-twitch muscles tire quickly, so we can’t sustain that intensity for long.

As the name suggests, slow-twitch muscle fibers work more evenly and at a leisurely pace, e.g. B. enable a runner to function during long marathons where energy must be sufficient.

Tiny “mimetic” muscles help form facial expressions in mammals. In humans, these muscles contain many fast-twitch fibers that allow us to form facial expressions quickly and easily — imagine flashing a big smile in response to a joke or a compliment.

The study, presented Tuesday at the American Association for Anatomy annual meeting in Philadelphia, examined fibers in facial muscle samples from wolves and domestic dogs.

The results showed that wolves have a lower percentage of fast-versus-slow-twitch fibers compared to today’s domesticated dogs. Slow-twitch muscles around the eyes and face would be helpful for wolves when howling, the researchers said, while more fast-twitch muscles would help dogs attract their owners’ attention with short, quick barks and more varied expressions.

“These differences suggest that faster muscle fibers help a dog communicate effectively with humans,” Burrows said.

Wolves also lack another ability that most dogs have, according to a previous stud from 2019j by Burrows and her team. This study found that dogs have a muscle called the levator anguli oculi medialis that can raise their inner “eyebrow,” making the eye look larger and more childlike. A Study 2013 Found dogs that do this often are more likely to be adopted.

“This eyebrow movement creates the expression of ‘dog eyes’ that resembles the facial expressions humans make when we’re sad, making them compelling and leading to a nurturing human response,” said co-author Madisen Omstead, laboratory director at the Rangos School of Health Scientific Department of Physiotherapy.

“We also know that we still unconsciously select these traits in dogs,” Omstead said, pointing to a Study 2013 showing that dogs that use these expressions more often “found new homes more quickly than less expressive dogs, reinforcing this type of evolutionary scenario even today.”

Another muscle called the retractor anguli oculi lateralis pulls the outer one Corners of the eyelids toward the ears, creating what humans would call an “eye smile.” The 2019 study found that while wolves had some of this muscle fiber, most domesticated dogs had a more developed muscle and used it frequently.

The exception to this rule is the Siberian husky, which is more closely related to wolves than many other breeds, the researchers said.

If muscles that allow your dog to smile and look cute 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 researchers according to human mothers and their infants.

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