Dogs use blinking to communicate friendliness and build social bonds with their owners, scientists from the University of Parma in Italy have discovered.
Researchers found that dogs started blinking faster when watching video footage of a human blinking, but the response only occurred if the person in the video was their owner.
The study showed that this effect was strongest when the owner shown in the recording was a woman.
In contrast, when the animals were shown videos of people staring straight ahead with their eyes open, their blink rate remained completely unchanged.
Testing how dogs respond to human blinking
To test how dogs react to visual cues, researchers showed 35 dogs videos in which humans were either blinking or staring straight ahead.
Lead author Dr Chiara Canori told the Daily Mail that the findings suggest canine communication is more sophisticated than previously realized.
"I believe that it suggests that dog-human communication may be more subtle and responsive to social relationships than we actually recognise," Dr Canori said.
"There may be a much richer layer of communication in these small, overlooked changes in behaviour, and learning to recognise and acknowledge them could help us better understand our dogs," she added.
Dr Canori pointed out that blinking primarily serves a biological function to protect the ocular surface.
"At its most basic level, blinking is a physiological behaviour that protects the eye and maintains the ocular surface," Dr Canori said. "What is interesting is the possibility that this very old, automatic behaviour may also have acquired some social relevance."
The authors cautioned, however, that they cannot yet determine whether these blinks carry any specific meaning beyond social engagement.
Social context and nonverbal communication
"Our study does not show that a dog is deliberately 'saying something' every time it blinks; rather, it suggests that this apparently simple and automatic behaviour can be influenced by the social context," Dr Canori explained.
She noted that the selective reaction demonstrates how deeply dogs evaluate social connection.
"The fact that dogs modulated their blinking depending on whether the human was their owner suggests that their responses are not simply triggered by seeing a human face or movement, but may be influenced by the social relevance of that particular person," Dr Canori said.
"So the connection between dogs and humans is built not only through obvious signals such as vocalisations or gestures, but also through these much more subtle, dynamic behavioural cues," she added.
Facial expressions and scent recognition in dogs
The discovery builds on earlier research showing that dogs possess remarkable skills in interpreting human emotional states.
Previous studies have established that dogs can tell the difference between human happiness, anger, fear and sadness from facial expressions alone.
Researchers discovered that seeing a human smiling lights up a unique region of a dog's brain, which does not react to negative facial expressions.
Separate studies have also demonstrated that dogs have the unique ability to smell human stress in sweat and on breath.
Blinking signals across the animal kingdom
Blinking has also been shown to carry social relevance in other animals, notably cats.
Cats will return their owners' slow blinks as a sign of affection, and felines are more likely to approach people who have blinked at them first.
History of canine domestication
The subtle bond between dogs and humans is the product of tens of thousands of years of co-evolution.
A genetic analysis of the world's oldest known dog remains revealed that dogs were domesticated in a single event by humans living in Eurasia around 20,000 to 40,000 years ago.
Dr Krishna Veeramah, an assistant professor in evolution at Stony Brook University, told the Daily Mail that domestication was a gradual evolutionary process.
"The process of dog domestication would have been a very complex process, involving a number of generations where signature dog traits evolved gradually," Dr Veeramah said.
"The current hypothesis is that the domestication of dogs likely arose passively, with a population of wolves somewhere in the world living on the outskirts of hunter-gatherer camps feeding off refuse created by the humans," he added.
"Those wolves that were tamer and less aggressive would have been more successful at this, and while the humans did not initially gain any kind of benefit from this process, over time they would have developed some kind of symbiotic relationship with these animals, eventually evolving into the dogs we see today."
