Dogs selectively bred thousands of years ago to achieve perfect puppy dog eyes

By Joe Morgan via SWNS

Dogs were selectively bred by humans thousands of years ago to achieve the perfect "puppy dog eyes," according to a new study.

Adoring and pleading expressions in dogs are actually intended so they can make more human-like faces, say scientists.

The more they pull off that "puppy dog eye" trick, they were not only given more treats but bred in order to keep that desirable trait going.

This trait to form facial expressions was achieved through thousands of years of selective breeding.

In the study, researchers analyzed the anatomy of tiny muscles used to form facial expressions called mimetic muscles.

In humans, these muscles are dominated by "fast-twitch” myosin fibers that contract quickly but also fatigue quickly, which explains why we can form facial expressions rapidly but not hold them for long.

Muscle cells with more “slow-twitch” fibers are more efficient for long, controlled movements and don’t tire as quickly.

For the study, researchers compared the myosin fibers in facial muscle samples from wolves and domesticated dogs.

The results revealed that, like humans, both dogs and wolves have facial muscles that are dominated by fast-twitch fibers, but wolves have a higher percentage of slow-twitch fibers relative to dogs.

Having more fast-twitch fibers allows greater facial mobility and faster muscle movement, enabling small movements such as a raised eyebrow and the short, powerful muscle contractions involved in barking.

Slow-twitch fibers, on the other hand, are important for extended muscle movements such as those wolves use when howling.

Dogs also have an additional muscle that is absent in wolves and contributes to the "puppy-dog eye" expression.

Professor Anne Burrows, at Duquesne University in Pittsburgh, said: "Dogs are unique from other mammals in their reciprocated bond with humans which can be demonstrated through mutual gaze, something we do not observe between humans and other domesticated mammals such as horses or cats.

“Our preliminary findings provide a deeper understanding of the role facial expressions play in dog-human interactions and communication.”

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

“Throughout the domestication process, humans may have bred dogs selectively based on facial expressions that were similar to their own, and over time dog muscles could have evolved to become ‘faster,’ further benefiting communication between dogs and humans."

The research was presented at the American Association for Anatomy at Experimental Biology annual meeting.