Dogs have evolved their “sad eyes” expression in order to help endear them to humans, a study found.
University of Portsmouth scientists compared the anatomy and behaviour of dogs and wolves.
Their findings suggest the facial structure of dogs changed over thousands of years specifically to enable them to communicate with humans.
A university spokesman said: “Dogs have a small muscle that allows them to intensely raise their inner eyebrow, which wolves don’t.
Dr Juliane Kaminski, who led the research, said the evidence was “compelling” that dogs developed the muscle after they were domesticated from wolves.
She said: “When dogs make the movement, it seems to elicit a strong desire in humans to look after them.
“This would give dogs that move their eyebrows more a selection advantage over others and reinforce the ‘puppy dog eyes’ trait for future generations.”
Psychologist Kaminski’s previous research showed dogs move their eyebrows significantly more when humans are looking at them.