There's a reason humans melt when they see 'puppy dog eyes,' new research reveals – USA TODAY

Ever wonder why dogs are able to melt hearts the way they do?
A group of researchers in the U.S. and the United Kingdom may have an answer for you.
As it turns out, researchers discovered dogs have a facial muscle that has evolved over the past 33,000 years, making their eyes look bigger and their faces sadder, younger and cuter, reeling in the humans who come across them.
In other words, “puppy dog eyes” are real, dogs are manipulating humans and it’s all thanks to domestication.
Researchers deemed the expression “the AU101 movement” and came to the conclusion after using coding and software to analyze the facial expressions of nine gray wolves and 27 dogs in the United Kingdom.
The group’s initial study, “Evolution of facial muscle anatomy in dogs,” was published in 2019 by the peer-reviewed journal Proceedings of the National Academy of Sciences of the United States of America,” or PNAS. Tuesday, one of the researchers presented the latest findings on how dogs’ facial muscle makeup is more similar to humans at an Experimental Biology meeting in Philadelphia.
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For their initial experiment, the researchers dissected dog and wolf heads to study their facial muscles, finding that dog and wolf faces are pretty much the same minus one muscle around the eye: the levator anguli oculi medialis muscle, also known as LAOM.
Amanda Lee, an assistant professor in human-animal interactions at Carroll University in Wisconsin who is not affiliated with the study, said the finding showed clearly how different dogs and wolves faces are structurally. 
“Once the paper came out, it was just such an enlightening thing to see that ‘Oh my gosh. Yes. Here’s the scientific backing,'” Lee said.
While dogs have the LAOM, wolves have muscle fibers surrounded by connective tissue, and sometimes, a tendon that blends with a different muscle. So, it’s more difficult for wolves to raise the inner corner of their brows and perform the “puppy dog eyes” act.
What’s most shocking is that the muscle developed in just 33,000 years since humans domesticated dogs, said Rui Diogo, an associate professor in the College of Medicine at Howard University who worked on the project.
For example, it took 6 million years for differences to show up in human and chimpanzee head muscles, Diogo told USA TODAY.
Diogo also said that the inner eye muscle is prevalent in a subgroup of dogs and that they mainly use the muscle when they are around humans.
“Clearly, they are cautious,” Diogo said. “They are doing that on purpose. It’s really impressive that they literally are using that to manipulate us in a way.”
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Anne Burrows, a professor in Duquesne University’s Rangos School of Health Sciences, said all mammals have both fast-twitch and slow-twitch fibers in their muscles. Fast twitch fibers contract rapidly, but they also get tired quickly, making it difficult to hold facial expressions for long periods of time.
Dogs’ faces are made of almost all fast-twitch fibers, allowing them to make facial expressions like humans. Wolves aren’t able to move their faces in the same way.
According to the researchers, domestication and the desire to appeal to humans transformed dogs’ facial muscle anatomy so they could communicate with them — and in a record amount of time.

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