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How Dogs Evolved To Be So Cute: More Human-Like Facial Muscles

    a labrador retriever

a labrador retriever
Photo: Simon Lees/PhotoPlus Magazine/Future (fake images)

The new preliminary data offers insight into why we may find dogs so lovable. One study found that dogs generally have faster facial muscles than wolves, muscles that allow them to react quickly with more expression, similar to humans. These same muscles may also help explain why dogs tend to bark, while wolves tend to howl.

That dogs can easily enter our hearts is no secret. But for years, researcher Anne Burrows and her colleagues have been trying to figure out how dogs have evolved over the millennia to become the lovable bums we know and love. Her previous research has He suggestedfor example, that dogs have a certain muscle largely absent in wolves that allows their eyes to open wide to create that “puppy face” appearance.

His latest research, being submitted this week at the annual meeting of the American Anatomy Association, adds further evidence to the notion that dog faces have become naturally suited to win us over.

The team looked at muscle tissue taken from a variety of dog breeds and the gray wolf under a microscope, looking for two different types of muscle fibers in particular: fast-twitch fibers and slow-twitch fibers. Fast twitch fibers can contract quickly but wear out sooner, while slow twitch fibers are the opposite and allow for longer lasting expressions. Tissues were taken from the orbicularis oris muscle (OOM), which surrounds the mouth, and the zygomaticus major muscle (ZM), located along the cheek. Both are important for creating facial expressions in dogs and humans, and the researchers looked specifically at the ratio of slow-twitch and fast-twitch fibers in these muscles.

Gray wolves and domestic dogs had fast-twitch fibers, the team found. But the percentage of fast-twitch fibers was substantially higher in the latter group: in dogs, between 66% and 95% of the fibers in these samples were fast-twitch, while the average in wolves was around 25%. By contrast, just under 30% of the fibers were slow-twitch in wolves, while only 10% were slow-twitch in dogs.

The researchers are careful to point out that their findings are preliminary and have yet to go through the typical peer-review process. But the ratio of fast-twitch and slow-twitch muscles seen in these dogs is similar to what has been documented in human faces, they note. And that suggests that modern dogs and their faces, following their split from the wolf lineage tens of thousands of years ago, have evolved to look more like us over time.

“It helps us conceptualize what Upper Paleolithic humans, roughly 40,000 years ago, valued when they domesticated dogs,” Burrows told Gizmodo in an email. “Because we and dogs communicate with each other using facial expressions, Upper Paleolithic humans must have wanted, consciously or unconsciously, a dog that used facial expressions in a similar way.”

The evolution of these faster facial muscles may not only have changed dogs’ ability to express themselves, but also the way they communicate verbally, Burrows said. While wolves occasionally produce short-lived barks, they more often stick to longer-lasting howls, and the reverse is generally true for dogs. The team theorizes that these behaviors are directly influenced by the facial muscles that each line of canines now work with.

“Howling requires a sustained muscular contraction of the muscles around the mouth to form a funnel shape that can last as long as a wolf barks. Barking is a short, staccato activity that requires little sustained muscle contraction,” Burrows explained. “So at some point in the dog domestication process, we selected faces that were fast in dogs, faces that could quickly make meaningful facial expressions to communicate with us, but we also selected a very fast face, one that could produce this new sound. . -bark.”

Our human ancestors might even have encouraged a shift from howling wolf-like dogs to modern barking dogs, the researchers argue, as they might have preferred canine companions who could quickly inform them of approaching danger or other necessary alerts.

The team plans to collect more data from facial muscles before submitting their findings for peer review in late summer, Burrows said. And they won’t stop there in trying to trace the origins of modern dogs. His next goal is to study and compare the ear muscles of dogs and wolves, to understand how they may be involved in social communication and hearing.

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