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New research suggests that over thousands of years of dog domestication, people preferred pups that could pull off that appealing, sad look. Photo: AP

How dogs learned to manipulate us with their sad puppy eyes, according to scientists

  • Pooches use the muscle to raise their eyebrows and make the babylike expression
  • That muscle is virtually absent in their ancestors, the wolves
Pets

Ever wondered how dogs learned to use their “puppy eyes” to bend us to their will?

It turns out our pet pooches have evolved human-like eyebrow muscles, which let them make the sad faces that melt our hearts, according to a new study published on Monday in the Proceedings of the National Academy of Sciences (PNAS).

It involved dissecting the cadavers of domestic dogs and comparing them to those of wild wolves, our best friends’ ancestors, whom they branched off from around 33,000 years ago (don’t worry, no animals were killed for the research).

A separate part of the study saw scientists videotaping two-minute interactions between dogs and a human stranger, then repeating the experiment with wolves, to closely track how much they used a specific muscle around the eye that produced an inner eyebrow raise.

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The researchers found two muscles around the eye were routinely present and well formed in the domestic dogs, but not the wolves, and only dogs produced high-intensity eyebrow movements as they gazed at the human.

“It makes the eye look larger, which is similar to human infants,” Professor Anne Burrows of Duquesne University in Pittsburgh, who was one of the co-authors, said.

This diagram shows a comparison between dog and wolf facial muscles. A study suggests that over thousands of years of dog domestication, people preferred dogs that could pull off the ‘puppy dog’ eyes look. Photo: AP

“It triggers a nurturing response in people.”

The study suggests ancient canines with expressive eyebrows might have elicited that nurturing from humans and that care would have given the animals a selection advantage that allowed them to pass on puppy-dog eyes to their descendants.

The current study was led by Juliane Kaminski at the University of Portsmouth and also included researchers from Howard University in Washington and North Carolina State University.

It builds on past work, including a notable 2015 paper by a group of researchers in Japan that showed that gaze exchange between humans and their pet dogs led to a mutual spike in the so-called love hormone oxytocin, similar to an effect seen between human mothers and their babies.

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Evan MacLean at the University of Arizona called the findings fascinating, but cautioned that the muscle difference could be an indirect effect of other changes rather than a specific response to human influence.

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.

But he noted 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.

Additional reporting by Associated Press and The Washington Post

This article appeared in the South China Morning Post print edition as: cientists take a peek behind those sad puppy dog eyesWhy ‘puppy eyes’ have that cute look
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