What is behind those hard-to-resist puppy dog eyes? New research suggests that over thousands of years of dog domestication, people preferred pups that could pull off that appealing, sad look, and that encouraged the development of the facial muscle that creates it.
Today, pooches use the muscle to raise their eyebrows and make the baby-like expression. That muscle is virtually absent in their ancestors, wolves.
“You don’t typically see such muscle differences in species that are that closely related,” said Anne Burrows of Duquesne University in Pittsburgh, an author of the study released on Monday by the Proceedings of the National Academy of Sciences.
Photo: AFP
Dogs differ from wolves in many ways, from having shorter snouts to their different sizes and more expressive faces. Unlike wolves, dogs rely heavily on human eye contact, whether to know when someone is talking to them or when they cannot solve a problem, such as hopping a fence or getting out of the door.
Burrows and her colleagues examined the eye muscles in the cadavers of six dogs and two wolves. They found dogs have a meaty eye muscle to lift their eyebrows and make puppy dog eyes, but in wolves, the same muscle was stringy or missing.
The scientists also recorded 27 dogs and nine wolves as each stared at a person. Pet pooches frequently and intensely pulled back their eyebrows to make sad expressions, while the wolves rarely made these faces, and never with great intensity.
The researchers believe dogs, over their relatively short 33,000 years of domestication, used this eye muscle to communicate, possibly goading people to feed or care for them — or at least take them out to play — and people obliged.
Dog experts not involved with the study were impressed.
“The implications are quite profound,” said Brian Hare from Duke University, who edited the article.
These muscles almost certainly developed because they gave dogs an advantage when interacting with people, and people have been unaware of it, Hare wrote in an e-mail.
Evan MacLean at the University of Arizona said the findings were fascinating, but cautioned that the muscle difference could be an indirect effect of other changes.
Clive Wynne of the Canine Science Collaboratory at Arizona State University said: “Kudos to the researchers for thinking of a cool way to investigate an important aspect of dogs’ success” with humans.
However, he said in an e-mail that the study has a few snags, particularly the small sampling — only five dog breeds were examined and videos were mainly of Staffordshire bull terriers — and the lack of background information about each animal.
Burrows said she is planning follow-up studies to examine more breeds.
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