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Those melt-your-heart puppy eyes? Humans could be responsible for it!4 min read

April 13, 2022 4 min read


Those melt-your-heart puppy eyes? Humans could be responsible for it!4 min read

Reading Time: 4 minutes

Collective *aww*

If you’ve had a dog companion at home, or even if you’ve associated with our furry canine friends, then you definitely have come across those puppy-dog eyes. Those sad eyes that can make even the toughest of us melt is a unique characteristic of dogs. However, new studies say that this adorable look is something us humans may have had a big role to play in.

Scientists suggest that domesticated dogs may have evolved extra facial muscles to win people over with their adorable expressions. Humans may have contributed to the heart-warming look through thousands of years of selective breeding for the animated faces, a study finds.

“Dogs are really unique from any other domesticated animals in that they reciprocate a bond with their humans. They truly are our companions,” says study author Madisen Omstead, a biologist at Duquesne University in Pittsburgh, to New Scientist. “They demonstrate this through their mutual gaze – that ‘puppy-dog eye’ look that they give us.”

In humans, tiny muscles around our eyes and mouths are responsible for small, quick facial expressions like raising an eyebrow. Our facial muscles, called mimetic muscles, are powered by fast-twitch myosin fibres that tire quickly, which is why we can can’t hold them these expressions for very long, say studies. Other muscles contain slow-twitch myosin fibres used for long, controlled movements.

These are the muscles in humans that are responsible for facial expressions.
Photo: anatomy.com

The study, presented at the American Association for Anatomy annual meeting in Philadelphia, US, examined fibres in facial muscle samples from both wolves and domesticated dogs.

Evolutions from wolf to woof! Photo: petbeings.com

Results showed wolves have a lower percentage of fast- verus slow-twitch fibres compared with today’s domesticated dogs. Having slow-twitch muscles around the eyes and face would be helpful to wolves as they howl, the researchers said, while having more fast-twitch muscles would help dogs get their owners’ attention with short, fast barks and more varied expressions.

“These differences suggest that having faster muscle fibres contributes to a dog’s ability to communicate effectively with people,” Burrows said.

Wolves also lack another ability that most dogs have, according to a previous 2019 study by Burrows and her team. That study found dogs have a muscle called the levator anguli oculi medialis, which can raise their inner “eyebrow,” thus making the eye look larger and more infant-like.

“This eyebrow movement creates the ‘puppy-dog eyes’ expression, resembling facial expressions humans make when we are sad, making them irresistible and resulting in a nurturing response from humans,” said co-author Madisen Omstead.

“We also know that we are still unconsciously selecting these characteristics in dogs,” Omstead said, pointing to a 2013 study that showed dogs who use those expressions more frequently “were re-homed more quickly than less expressive dogs, reinforcing this type of evolutionary scenario even today.”

Another muscle, called the retractor anguli oculi lateralis muscle, pulls the outer corners of the eyelids toward the ears, in effect producing what humans would call an “eye smile.” The 2019 study found that while wolves had a bit of this muscle fibre, most domesticated dogs had a more fully 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 muscles that allow your dog to smile and look sweet aren’t enough, looking into the eyes of our furry best friends also appears to trigger an ‘oxytocin feedback loop‘ between humans and our dogs — much like the one that exists between human mothers and their infants, according to researchers.

So, next time your dog gives you those eyes, you know that evolution has a lot to do with why you just cannot resist that face!

Sources: CNN, New Scientist

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