New research found that evolution played a big part in why our furry friends are able to communicate without making a sound.
Cute Cocker Spaniel Puppy Eyes
Credit: Busybee-CR via Getty Images

Most dog owners know when their pup wants something or is vying for their attention-without whining or barking, dogs are known for "puppy eyes" that convey a sense of emotion, even to humans. Using just their eyes to get someone's attention may be more of a recent canine trait, however, as new research claims dogs didn't always have the muscles around their eyes necessary to make the expressions that melt their owners' hearts. According to a study published in the journal Proceedings of the National Academy of Sciences, dogs evolved to have to have the facial muscle that enables them to mimic what researchers call an "infant-like" expression that often prompts a "nurturing response" from humans around them.

According to the study, dogs use their eyebrow muscles to create what's known as "expressive eyebrows" and, combined with rounded eyes, use the expression to knowingly influence anyone around them. "When dogs make the movement, it seems to elicit a strong desire in humans to look after them," the study reports. This particular eyebrow muscle has become stronger over time to allow dogs' eyes to "appear larger, more infant-like, and also resembles a movement humans produce when they are sad."

The group of researchers behind the study examined the eye muscles in six different deceased dogs and two different wolves-the wolves didn't have the same eyebrow muscle that the dogs did. The scientists also recorded 27 different dogs and nine wolves as they interacted with nearby humans; the pups frequently flexed their eyebrow muscles to make sad expressions, whereas the wolves in the experiment rarely conveyed the same expression. Previous research from England's University of Portsmouth has also shown that dogs are more likely to use puppy eyes when a human is looking at them, which suggests that they certainly know how to influence humans, the BBC reports.

This new study suggests that the evolutionary trait has been passed down to modern dogs because owners chose to breed pups who had it in the first place; an "unconscious preference" to protect and breed dogs who used puppy eyes over the years. Dogs may have developed the trait soon after they were domesticated from wolves, but researchers say their work has suggested that facial change has occurred over the thousands of years that dogs have lived alongside humans.


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