Dogs have developed their "sad eyes" facial look so as to draw humans’ attention and hearts, said a new study published at the University of Portsmouth scientists.
Scientists compared the anatomy and behaviour of dogs and wolves, and found that the facial structure of dogs had gradually changed to enable them to communicate with humans.
"Researchers found that the facial musculature of both species was similar, except above the eyes,” a university spokesman said.
"Dogs have a small muscle, which allows them to intensely raise their inner eyebrow, which wolves do not,” he pointed out.
"The authors suggest that the inner eyebrow-raising movement triggers a nurturing response in humans because it makes the dogs' eyes appear larger, more infant-like and also resembles a movement humans produce when they are sad,” he added.
According to Psychologist Dr Juliane Kaminski, who led the research, “the evidence is compelling that dogs developed a muscle to raise the inner eyebrow after they were domesticated from wolves.”
"We also studied dogs' and wolves' behaviour and, when exposed to a human for two minutes, dogs raised their inner eyebrows more and at higher intensities than wolves,” she said.
"The findings suggest that expressive eyebrows in dogs may be a result of humans' unconscious preferences that influenced selection during domestication.”
"When dogs make the movement, it seems to elicit a strong desire in humans to look after them,” she added.
"This would give dogs that move their eyebrows more a selection advantage over others and reinforce the 'puppy dog eyes' trait for future generations."