Now, new research by Japanese scientists suggests that a dog’s eyes can water with happiness when it’s reunited with its owner after a period of absence. The tears could help cement the bond between humans and dogs — a relationship that dates back tens of thousands of years.
Like humans, dogs have tear ducts filled with tears to keep their eyes clean and healthy. But tears in dogs, which don’t usually fall the way they do when humans cry, had not previously been associated with emotions.
Takefumi Kikusui, a professor at the Laboratory of Human-Animal Interaction and Reciprocity at Azabu University in Japan, decided to study dog tears after observing one of his two Standard Poodles when she had puppies six years ago. He noticed her eyes watered as she nursed her puppies.
“We found that dogs shed tears that are associated with positive emotions,” Kikusui, co-author of the study published Monday in the journal Current Biology, said in a press release.
“We also discovered oxytocin as a possible underlying mechanism,” Kikusui said, referring to the hormone sometimes called the love or maternal hormone in humans.
To investigate the link, Kikusui and his team measured the amount of tears in 18 dogs using a standard test known as the Schirmer tear test. It This involved a strip of paper placed in the dogs’ eyelids for a minute before and after they were reunited with their owners after five to seven hours of separation.
“Tear volume was evaluated by the length of the wet part on the STT. The baseline was about 22mm and owner reunion increased by 10%,” Kikusui explained via email.
Using 20 dogs, the researchers then compared the amount of tears before and after reunion with theirs Owners and people with whom the animals were familiar. Only the reunion with the owner made the tears flow.
To understand whether oxytocin played a role in tear production, a solution containing the hormone was applied to the surface of 22 dog eyes. Tear volume increased significantly after using oxytocin compared to a control solution.
There’s still a lot researchers don’t know about dog tears. People often cry in response to negative emotions, but researchers haven’t tested whether dogs do the same. They also don’t know if a dog’s ability to tear has a social function in the dog World.
said Kikusui It was possible that humans would take better care of dogs that got teary-eyed. His team showed 74 persons pictures of dog faces with and without artificial tears in them and asked them to rank the animals. People reacted more positively when they saw dogs with watery eyes.
“Dogs have become partners with humans,” Kikusui said in a statement, “and we can form bonds.”