There are few things more enjoyable than returning home and meeting the love of a pet dog. New research shows that the happiness of being reunited with its owner can cause a dog to shed tears. Describing their findings in the journal Current Biology, the study authors say that dogs’ emotional response to seeing their favorite human occurs to win our hearts and inspire us to be better owners.
“Unlike any other animal, dogs have evolved or domesticated by communicating with humans and have acquired superior communication abilities by making eye contact with humans,” the researchers write. “Through this process, tears may play a role in eliciting protective behavior or nurturing behavior from their owners. , which in turn can lead to deepening interrelationships and interspecies bonding.”
But unlike us crying humans, crying dogs don’t produce the kind of tears that roll down their cheeks and wet the pillow. Instead, they simply fill and tear, creating an irresistible puppy dog eye effect.
So instead of counting the tears, the study authors measured the volume of tears in the dogs’ eyes when they were at home with their owner and then when they were reunited with their owners five to seven hours apart. The results showed that tear volume increased significantly when dogs were reunited with their owners, not when they were reintroduced to familiar people who weren’t their owners.
Previous research has shown that interactions between dogs and humans trigger the release of the so-called “love hormone” oxytocin in both species. Because oxytocin plays a central role in social bonding and emotional responses, the study authors suggest that dogs’ crying behaviors may be triggered by this neuropeptide.
To investigate, they gave oxytocin to the dogs’ eyes and found that it caused an increase in tear volume. The absence of such a reaction when a different peptide solution was added to the eyes of animals confirms that the tear is not caused by irritation.
“We found that dogs shed tears associated with positive emotions,” study author Takefumi Kikusui said in a statement. “We also made the discovery of oxytocin as a possible underlying mechanism.”
Finally, the study authors showed people photos of dogs’ faces with and without tears and asked them to rate how much they would like to look at the depicted animals. Overall, participants expressed a greater urge to stare at dogs with tearful eyes, noting that tear production can serve to activate our emotions and increase our desire for protection.
“Dogs have become humans’ best friends and we can bond, too. In the process, it may be possible for dogs who have tears in their eyes to be given more attention by their owner,” says Kikusui.
While the results of these experiments show that dogs shed tears in response to happy encounters with humans, it is not known whether they also produce tears when they are sad. Also, the researchers can’t say with certainty whether tears have any function in mediating social interaction between dogs, or whether the puppies’ eyes that affect us exist solely to stimulate human emotions.
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