Scientists from Japan’s Azabu University have proven that dogs produce tears in cases of positive emotions, as happens, for example, when they meet their owner after a long separation.
Dogs reportedly have human-like social-cognitive skills, which are thought to result from convergent evolution with humans1. Eye contact plays a pivotal role in attachment behavior in dogs, with eye contact between dogs and humans eliciting human caregiving behavior. It is also hypothesized that canine tear production during reunions with owners can facilitate human caregiving, a phenomenon which has similarly been reported in human children.
Furthermore, dogs have evolved muscles responsible for raising the inner eyebrows, which trigger nurturing behavior in humans4. A dog’s gaze initiates interactions with its owner, and stimulates secretion of oxytocin, a key hormone involved in bond formation, in owners.
The journal Current Biology notes that veterinarians first noticed tears in a dog’s eyes when she was breastfeeding puppies, and it became clear to them that this was due to the hormone oxytocin and positive feelings.
And veterinarians conducted an experiment, during which they followed what happens when do-gs meet their owners. They discovered that the amount of tears increases in her eyes when she meets someone she knows, while the amount of tears does not change when she meets someone she does not know. After that, the researchers increased the level of the hormone oxytocin in the body of the participating do-gs, which led to their tears.
The researchers conducted a third experiment, which involved asking people to rate images of dogs with and without tears in their eyes. It became clear to them that the pictures with tears arouse more feelings then.
The researchers concluded that tears help dogs bond more closely with humans.