But researchers believe they are getting close to finding the answer. A group of neuroscientists from the University of Cambridge recently declared that non-human animals like dogs have emotions and the capacity to show intentional behaviors.
However, K.C. Thiesen, the director of pet care issues for the Humane Society of the United States, advises people not to think a dog's smile is the same as a human's smile. While almost all mammals have some sort of facial expression that they use when they are trying to be friendly, this expression in dogs doesn't always mean approachability. When misinterpreted, it can lead to unpleasant canine encounters.
"Learning what [a] dog's body language can tell you is super important, since a dog 'smiling' may or may not be approachable and friendly," says Thiesen.
Maybe not a smile
Juliane Kaminski, a researcher studying dog cognition, also advises caution when interpreting a dog's facial expression as a smile.
Dog owners, she says, should learn how to read the behavior of their pups instead because there's zero data saying that a dog's smile is really a smile. Humans have a tendency to anthropomorphize, especially when it comes to their pets. This makes them more likely to misinterpret their dog's facial expressions. (Related: Dogs found to be more attracted to SMILING human faces.)
According to a study published in the journal Scientific Reports, dogs can show distinctive facial movements in response to different emotional stimuli. However, these facial movements are not the same as those displayed by humans under similar conditions.
For instance, dogs often use a relaxed, open-mouth expression when they're happy and trying to invite other dogs to play. However, there's no evidence suggesting that dogs use this intentionally to try to communicate something to humans.
This finding may be disappointing, especially for dog owners and dog lovers out there. But Kaminski believes more research needs to be done, and they should include objective research techniques, such as the facial action coding system (FACS), which can measure every minute facial motion dogs make when interacting with people.
Puppy dog eyes
FACS-based research may be able to shed light on the meaning of a dog's smile, as a study done by Kaminski herself has proven. In it, they demonstrated that a dog's "puppy dog eyes" expression is something the animals developed to help improve their relationship with humans. This facial action of inwardly raising the brows makes a dog's eyes look larger and more infant-like, thus generating an emotional response from humans.
"When dogs make the movement, it seems to elicit a strong desire in humans to look after them," said Kaminski. This gives those dogs a selection advantage over others and reinforces the "puppy dog eyes" trait for future generations.
Conversely, scientists have found that wolves, dogs' closest living relatives, don't have the muscle needed to make this expression in their eyebrows. This strongly suggests that the "puppy dog eyes" is an evolutionary response to dogs' relationship with humans.
These findings have led Kaminski to believe that future research involving FACS technology can help explain the mystery of a dog's smile. Dogs are really good at understanding human speech patterns and body language. Even chimps, the most closely related animals to humans, don't understand human gestures as well as dogs do. So whether or not man's best friend actually knows how to smile, it's clear that dogs understand people, and owners should try their best to communicate with their pets in ways dogs are capable of understanding.
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