There aren’t many things in life that can compare to the satisfaction of coming home to the love and companionship of a pet dog. A loving lick, a joyful jump, a heartwarming look, a wagging tail—when your dog is happy to see you, you can tell.
And according to recently completed research, the joy of being reunited with their favorite human can even make dogs cry a few happy tears.
The authors of a new study published Monday (August 22) in the peer-reviewed journal Current Biology found that the emotional response dogs have when they see their favorite human is designed to tug on our heartstrings so that we want to be better owners.
“Unlike any other animal, dogs have evolved or have been domesticated through communication with humans and have gained high-level communication abilities with humans using eye contact,” the researchers wrote.
“Through this process, their tears might play a role in eliciting protective behavior or nurturing behavior from their owners, resulting in the deepening of mutual relationships and leading to interspecies bonding.”
However, in contrast to humans who cry easily, blubbering dogs do not generate the kind of tears that run down cheeks and soak the pillow when they are sad.
For dogs, they simply start to choke up and get teary-eyed, which gives them the appearance of having adorable puppy eyes.
Instead of counting individual teardrops, the authors of the study examined the amount of tears that were present in the eyes of dogs when they were at home with their owners and again when they were reunited with their owners after being apart for five to seven hours.
According to the findings, the volume of the dogs’ tears greatly rose when they were reunited with their owners, but this effect was not observed when the dogs were reintroduced to familiar humans who were not their owners.
Dogs seem to share a special bond with their favorite human.
Previous studies have shown that interactions between dogs and humans cause both species to release oxytocin—also known as the “love hormone“—and people and dogs both share the same oxytocin receptors.
The authors of the study hypothesized that dogs’ overly affectionate behavior could be explained by oxytocin, as it is known to play an important part in social bonding as well as emotional responses.
“We also made the discovery of oxytocin as a possible mechanism underlying it,” said study lead author Takefumi Kikusui.
As part of the investigation, they found that giving oxytocin to the eyes of dogs induced an increase in the number of tears produced by the canines.
The fact that a different peptide solution was applied to the animals’ eyes and the same reaction was not seen demonstrates that the production of tears was not a response to irritation in the eyes of the animals.
“We found that dogs shed tears associated with positive emotions,” Kikusui said in a statement. “We also made the discovery of oxytocin as a possible mechanism underlying it.”
In the final step of the research, the authors showed people photos of dog faces with and without tears, and they asked the participants to rate the degree to which they desired to care for the animals shown.
Participants, on average, reported a larger impulse to care for dewy-eyed dogs, which suggests that the creation of tears may help to play on our emotions.
Although the findings of these experiments suggest that dogs can shed tears of joy in response to positive interactions with humans, it is unknown whether or not they also generate tears when they are feeling unhappy.
The researchers were unable to determine whether or not tears have any use in mediating the social contact between dogs, or whether or not puppy-dog eyes serve no purpose other than to make people feel all warm and fuzzy inside.
“Dogs have become a partner of humans, and we can form bonds,” explained Kikusui. “In this process, it is possible that the dogs that show teary eyes during interaction with the owner would be cared for by the owner more.”
Outside of humans, dogs are the only species known to possess this trait.
“We had never heard of the discovery that animals shed tears in joyful situations, such as reuniting with their owners, and we were all excited that this would be a world first,” said Kikusui.
Perhaps dogs truly are man’s best friend.
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