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Study Shows How 'Puppy Dog Eyes' Are an Evolutionary Key In Our Relationship

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Image Credit: Well Pet Coach


Humans and dogs have been partners for thousands of years, forming a strong bond that helped both creatures survive as social beings, hunting in packs, and cooperating in ways that have proven mutually beneficial. It’s logical to assume evolution has stepped in to serve or build on that partnership, and new research published in the Proceedings of the National Academy of Sciences (PNAS) has just detailed one particular way in which this has happened: Canines have evolved to present those ever-familiar puppy dog eyes as a tool for connecting with humans. 

Researchers in Britain and the United States compared the facial muscles of both wolves and domesticated canines — species that are obviously very similar and share an ancestral history, but at some point broke apart when dogs started to become domesticated by humans more than 30,000 years ago. This is when dogs started to change more drastically in physical ways to accommodate their new partnership, while wolves continued to live in the wild. 

Specifically, the heads of two wolves and four dogs were examined in the study. Most of the bone structure and facial features were similar or identical between the two, however, researchers found a noteworthy, major difference exists above the eyes. Dogs, as it turns out, have two well-formed muscles above the eyes that wolves either do not possess or were less developed.  

“You don’t typically see such muscle differences in species that are closely related,” Anne Burrows, a leader of the study and professor at Duquesne University in Pittsburgh, Pennsylvania, told the Associated Press.

The unique eyebrow-raising feature is what allows dogs to form the puppy dog eyes we’ve all seen a million times (and likely melted over), creating a nurturing feeling in humans when the eyes appear larger, as well as creating an expression that somewhat mirrors that of a human baby. It’s actually the exact same expression humans have developed as a way to convey sadness. 

“The evidence is compelling that dogs developed a muscle to raise the inner eyebrow after they were domesticated from wolves,” Comparative psychologist Juliane Kaminski from Britain’s University of Portsmouth said.

As a separate part of the study, researchers then observed how 27 dogs and nine wolves interacted with a human. When exposed to the person for two minutes, researchers observed the dogs raising their inner eyebrows more frequently and at a higher intensity than wolves. Technically, wolves have muscles that control function over this part of the eye, but the extra muscles dogs have developed allows them to make a more “intense” expression with what we’ve all come to call those “puppy dog eyes.” Researchers say dogs evolved to use this expression as a way to get humans to do things for them, like giving food, care, or attention. Instantly, you probably imagine getting that same look from your own dog and now realize there are tens of thousands of years of evolution at play here. Dogs rely heavily on eye contact as a way to process and interpret communication with humans, more so than through verbalized communications. In fact, dogs have a limited capacity for learning words. On 2009 study determined that the average dog has the ability to learn about 165 different words — a limited vocabulary compared to humans, of course, but also far beyond the typical “stop” and “no” commands we instinctively order. However, those 165 words actually include hand gestures as well, a vocabulary that’s equivalent to that of a developing two-year-old infant.  And the absolute smartest dogs, by this scale, have the capacity to learn as many as 250 words. The Border Collies, Poodles, and German Shepherds in the top of that pack are on par with a child at two and a half years. 

Meanwhile, another recent study in Italy, researchers sought out a way to determine if dogs learn commands better with verbal communication or physical gesture with 10 Golden retrievers and 15 Labrador retrievers, all recruited at the Italian School of Water Rescue Dogs and already qualified as water rescue teams. According to the report, the dogs were already trained to obey basic commands like "sit", "lie down”, "stay", "come", "fetch", and “turn" as well as hand signals. 

In the test, the dogs were given those same common commands both verbally and physically. First, the dogs were given four basic commands delivered by their owner using only hand signals. In the second test, the owners stood with their hands loosely by their sides and gave the same commands verbally. And finally, in a third test, the dogs were given verbal and physical commands at once. But the catch here was that the commands were always incompatible. “Lie down” was used with the gesture for sitting. ‘Sit down” was paired with the signal for lying down. “Come” was used with the signal for staying put, and “stay” was paired with the gesture indicating come here. 

What researchers found was that the dogs obeyed hand gestures on their own with no voice command 99% of the time, while verbal commands only commanded 82% correctness in behavior. When the hand gestures and voice commands were paired together, the dogs responded to hand gestures 70% of the time. So even when you’re verbally telling your dog something, he’s more than twice as likely to obey your body language or hand gestures as commands. 

With all this in mind, it’s easy to see how important this one simple gesture — dogs learning to use their eyes as a way to communicate with humans — has had a profound impact on our relationship. Over time, this simple expression could have been a major turning point in humans favoring dogs over wolves in our eventual partnership. 

Interestingly enough, one particular species of domesticated dogs in the study doesn’t have this feature of muscles above the eye, the Siberian husky, which the researchers referred to as an “ancient” breed.” They’re also the breed that probably most closely resembles wolves, something they suggest shows us the link between the two as one paired up with humans and another didn’t. According to Burrows, the study’s small sample size of dogs and wolves offers limited data, while the same work can now be extended to observing other animals that have developed long-lasting relationships with humans through domestication, like horses or cats. 

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