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A New Study Finds The Reason For Those Adorable Puppy Dog Eyes

According to a new study, humans bred dogs to have ‘puppy dog eyes‘ nearly 33,000 years ago.

That’s right, those cute, irresistible eyes are our doing! When compared with their genetic cousin, the wolf, they found that dogs have more “fast-twitch” facial muscles. This meant that dogs can mimic our facial expressions and give us those adorable little eyes that melt our hearts.

“Throughout the domestication process, humans may have bred dogs selectively based on facial expressions that were similar to their own,” said senior author Anne Burrows in a statement.

“Dogs are unique from other mammals in their reciprocated bond with humans which can be demonstrated though mutual gaze, something we do not observe between humans and other domesticated mammals such as horses or cats.”

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So what are fast-twitch muscle fibers? Fast-twitch fibers are muscles throughout the body that allow us to make sudden and powerful movements, like beginning to sprint. These muscles wear out quickly, and intensity can’t be kept up for a long time.

On the other hand, slow-twitch muscle fibers are the ones that allow us to keep going. If fast-twitch muscles are what allows runners to start sprinting, slow-twitch muscle is what gives us endurance and energy to last.

Source: Ali Tajran/Youtube

Minuscule “mimetic” muscles help mammals use facial expressions. These muscles have fast-twitch fibers, allowing us to make expressions easily and quickly.

The study presented at the American Association for Anatomy examined these facial fibers in both wolves and domesticated dogs. They found wolves have a much lower percentage of fast slow-twitch fibers, compared to domesticated dogs. Researchers pointed out that slow-twitch muscles in the face help the wolves howl, while fast-twitch muscles help our pet dogs get our attention on different variations of barks and other expressions.

“Over time dog muscles could have evolved to become ‘faster,’ further benefiting communication between dogs and humans,” Burrows said.

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

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Burrows and her team discovered another interesting ability of domesticated dogs back in 2019. They found that dogs have a muscle called the levator anguli oculi medialis, which can raise their eyebrow area, making it look like what we know as puppy dog eyes. Interestingly, another muscle dogs have in their face is called the retractor anguli oculi lateralis, which is what allows them to give an eye smile.

“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 coauthor Madisen Omstead.

This cute trait was likely formed through thousands of years of selective breeding. Whether people know it, they’re more likely to choose a dog at the shelter who is expressive, which reinforces the trait. A study in 2013 proved that more expressive dogs were more likely to be rehomed.

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