A discovery that further relates the dogs with human beings is research published in the journal Current Biology that analyzes the tears of dogs, reaching the conclusion that like men, they also cry with joy.
“We found that dogs shed tears associated with positive emotions,” said co-author Takefumi Kikusui from Azabu University in Japan in a statement Monday. “We also made the discovery of oxytocin as a possible underlying mechanism.” Oxytocin is known as the “love hormone.” In humans, it is like hugging
Kikusui and his colleagues made the discovery after one of his two poodles gave birth to puppies 6 years ago. They noticed that when his dog nursed the puppies, something changed in the animal’s face and there were tears. These tears do not fall as they usually do in humans, but they do fill their eyes with tears. “That gave me the idea that oxytocin might increase tears,” says Kikusui.
The team measured the volume of tears in dogs before and after meetings with their owners and compared that data to when the dogs met an unknown owner. Tear volume increased during owner reunifications, but not when dogs were reunited with non-owners. Additional work found that adding oxytocin to a dog’s eyes increased tear volume.
“We had never heard of the discovery that animals shed tears in joyful situations, such as meeting their owners, and we were all excited that this was a world first,” Kikusui said.