Dogs’ faces evolved to improve connections with people, study suggests

Dogs have evolved to have muscles in their faces that are very different from those of wolves, which means that they have changed in a way that makes them more appealing to people.

Kenji, a 13-week-old German shepherd puppy, looks to his puppy raiser, Cindy Tait, at a Guiding Eyes for the Blind Foundation class in Easton, Md. on Feb. 15.Carolyn Kaster / AP file

Unlike the wild wolves from which they descended, the faces of dogs have developed over tens of thousands of years to make them more appealing to humans, according to a new study.

The study found that dogs’ face muscles contain a considerably higher proportion of “fast-twitch” muscle fibers than wolves’, which scientists believe allows dogs to transmit their emotions to their owners more effectively.

The same scientists were engaged in the finding a few years ago that dogs had created a muscle above their eyes that they utilized to make their eyes appear larger and generate the lovable “puppy dog eyes” expression.

The muscle was found not to be developed in wolves, which means that “puppy dog eyes” are something that dogs have evolved to manipulate people with.

Taken together, the muscular alterations show that dogs’ faces have developed anatomically to better their interactions with people, according to project leader and biological anthropologist Anne Burrows, a professor of physical therapy at Duquesne University in Pittsburgh.

“There’s a significant difference between dogs and wolves,” she remarked. “They just don’t move their faces in the same way.”

Burrows and a colleague at Duquesne, animal physiologist Kailey Omstead, showed off some of their findings at the Experimental Biology 2022 meeting in Philadelphia on Tuesday.

They discovered that the muscles of dogs’ faces are made up of 66 to 95 percent fast-twitch fibers, whereas wolves have about 25 percent.

All mammals’ muscles, including humans and dogs, are made up of millions of fibers of a protein called myosin. Each muscle contains a mixture of fast-twitch fibers, which contract swiftly but fatigue quickly, and slow-twitch fibers, which contract slowly but do not tire as quickly.

Because the muscles in our faces are dominated by fast-twitch fibers, we can convey our ideas on our faces in an instant, but only for a short time. The muscles in our backs, on the other hand, are dominated by slow-twitch fibers that can withstand higher weights for longer periods of time.

“You can hold a 10-pound weight for a full minute,” Burrows explained. “However, you won’t be able to hold a smile in the mirror for a complete minute.” Because your face is dominated by fast-twitch fibers, your face muscles get tired.”

According to the findings of Burroughs and Omstead, the high proportion of fast-twitch fibers in the faces of dogs is now closer to that of humans than to that of wolves.

According to Burrows, this could be because of the process of domesticating dogs, which involves picking puppies who seem to be the most open to humans. This could make dog faces grow “faster” over time.

“When Upper Paleolithic people in Europe and Asia domesticated the first dogs some 40,000 years ago, they appear to have chosen pups with fast-moving faces,” she said.

Dogs’ face muscles may have evolved as well because prehistoric people favored dogs that barked—an action that relies on fast-twitch muscle fibers—over dogs that howled like wolves, which relies on slow-twitch fibers.

“They were choosing against that howling habit, and selecting for these new dogs that created this new sound, this bark,” she explains, implying that barking dogs were better at warning danger than howling dogs.

However, Marc Bekoff, emeritus professor of evolutionary biology and animal behavior at the University of Colorado, Boulder, cautions that the study’s findings are preliminary, and it’s possible that the facial muscles of dogs don’t make much of a difference in their personalities.

Bekoff has worked with coyotes and wolves that were born in the wild and were raised by humans. While the mature animals were not as obedient as dogs, he said that “hand-reared coyotes and wolves can converse successfully with humans.” “No one has ever investigated whether they communicate with people as well as dogs, but they are social animals.”

Burrows and Omstead highlight that when compared to dogs and wolves, the face muscles of domesticated horses and cats do not display the same modifications as wild horses and wild cats.

It has also been proposed that dogs exhibit a form of “neoteny,” in which they retain several characteristics of juvenile wolves in adulthood, such as their less aggressive personalities, while wolves grow out of them, possibly because such characteristics were favored by humans during the dog domestication process.

Evan MacLean, director of the University of Arizona’s Canine Cognition Center and a biological anthropologist, said future research could look into whether the proportion of fast- and slow-twitch facial muscle fibers varies with age in wolves, which could indicate that this, too, could be a result of neoteny.

h/t: NCB News


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