This Dog Study Is a Big Deal, If It Holds Up

We humans are known to well up with tears when we're particularly happy. Now a new study out of Japan suggests the same applies to dogs, a first-of-its kind assertion for any non-human animal, reports the Guardian. Dogs have tear ducts just as humans do, but the longstanding belief has been that the tears they produce (which tend not to fall) serve the purely functional purpose of keeping the eyes healthy and clean, explains CNN. The new study at Current Biology, however, makes the case that dogs' tears can be triggered by happiness. "We found that dogs shed tears associated with positive emotions," says Takefumi Kikusui of Azabu University in a news release.

In one part of the experiment, the researchers measured dogs' baseline tear volume (through a standard test known as the Schirmer test) and then compared it to the volume when a dog was reunited with its owner after several hours. Tear volume shot up. They also reunited the dog with a familiar person who was not the owner, and no such increase was seen. "If we accept the evidence of this paper, this is one of the most stunning discoveries in animal expression of emotions of all time," Clive Wynne, an expert in dog behavior at Arizona State University, tells the New York Times. However, he adds, "it would take a lot to convince." (For one thing, the study was small, involving only 20 dogs.)

In another part of the study, the researchers say they showed that oxytocin (the "love hormone") plays a role in the formation of dogs' tears. They administered either a solution with oxytocin or a control substance into dogs' eyes and found that the oxytocin mix produced more tears. Extending this experiment, they also found that humans looking at dogs with the resulting shiny eyes felt more nurturing toward them than to dry-eyed dogs. Among future areas of research to be explored: "We do not yet know if dogs show an increase of tears during a dog-dog reunion," says Kikusui. "We also do not know how dogs use tears to communicate with each other." (More dogs stories.)