Have you ever wondered if dogs cry? A team of Japanese scientists has concluded that they do, more specifically out of joy. Of course, the tears do not slide down their faces, but accumulate in the eyes. According to this study, published in Current Biology , dogs cry with joy when they are reunited with their owners (and only with them) after a period of absence.
Researchers recruited 18 dogs and found that when dogs were reunited with their owners, their tear volume increased by 10% compared to normal wetness. This did not happen if they saw a known person who was not their owner.
In the study, tear droplets were measured by placing absorbent paper against the dog’s eye for 60 seconds and recording how far the moisture reached.
In humans, a greater volume of tears is related to a greater arousal of emotions. The results of the dog study suggest that it is positive emotions that cause tears in the animals.
The researchers carried out another experiment in which they applied a solution containing oxytocin , known as the love hormone and which is associated with feelings such as trust, empathy and the creation of relationships, directly in the eyes of 22 dogs. What they saw was that the animals generated more tears when the oxytocin was applied in this way. From this they have concluded that the increase in oxytocin, which occurs, for example, when greeting a loved one, is possibly what triggers the extra tear production in dogs.
“We had never heard of the discovery that animals shed tears in situations of joy, such as reunion with their owners, and we were excited that it was a world first,” says animal behaviorist Takefumi Kikusui, who participated in the study. from Azabu University in Japan.
Although discovering that our dogs cry with happiness when they meet us again would be a revolutionary finding, other scientists do not agree with the experiment or its methodology.
At the moment, only humans cry as an emotional reflex. Other animals use the moisture in their eyes to remove dirt or clear vision . According to this, it is possible that as a result of the application of oxytocin, the dogs have generated more tears to “clean” the dirt in their eyes. Tears would not be, therefore, of happiness but cleansing. Kikusui does not think this is the case, as the control substance used in his experiments did not cause more tears in the dogs.
What is clear is that it is not easy to differentiate a tear of emotion and another of cleaning , so it would be necessary to carry out more studies to know if the tears of dogs when seeing their owners are of one type or another.
It would also be necessary to determine whether the watery eyes of dogs are due to a similar adaptation to the muscles that have developed around their eyes to put on “puppy eyes”, which are irresistible to humans, or would be a way of expressing their emotions. In line with this, scientists discovered that dogs that had watery eyes attracted more attention from humans than those that did not. To do this, they showed 10 photographs of dogs to 74 people who were asked to rate how they felt when they saw them. Moist-eyed dogs touched more people’s hearts.
“Dogs have become companions to humans, and we can bond,” says Kikusui. “In this process, it is possible that dogs that show watery eyes during interaction with the owner receive more care from the owner.”
Are we seeing in the eyes of our pets what we want to see? Only time and science will give us the answer.
Referencia: Murata, K., Nagasawa, M. et al. 2022. Increase of tear volume in dogs after reunion with owners is mediated by oxytocin. Current Biology. DOI: https://doi.org/10.1016/j.cub.2022.07.031
