Dogs that frequently portray child-like faces (raising their inner brows to make their eyes look wider) have higher chances of being selected by a prospective owner than the other dogs, according to a University of Portsmouth study.

Previous studies showed that humans are more inclined toward childlike faces (puppy dog eyes) in both infants and animals. But this is the first study that has found how childlike facial expressions play an important role in the selection of pet dogs.

For the study, Waltham Centre for Pet Nutrition and Portsmouth researchers developed a tool called 'DogFACS' to examine dogs' facial expressions. Using the tool, the researchers studied the eye movements of 27 dogs (Staffordshore Bull Terriers and Mastiff dogs aged seven months to eight years) in re-homing shelters. The tool recorded the number of times the pets produced puppy dog eye movements as a potential owner approached their pen.

Dogs, which made these cute child-like expressions, were able to attract an owner faster than those that did not.

"The results of this research suggest that wolves which produced childlike expressions may have been more tolerated by humans, and so modern dogs have inherited these features," Dr Bridget Waller, an expert in the evolution of social communication and the study's lead author, said in a statement.

"Our study suggests that dogs' facial movements have evolved in response to a human preference for childlike characteristics. In other words, we might have automatically opted for dogs which produced facial movements that enhanced their baby-like faces."

Waller said that making puppy dog eyes is associated with sadness by humans. This is the reason why owners can't resist selecting dogs with these cute facial expressions as they feel that they are just responding to their sadness.

 "The results suggest dogs have evolved childlike facial features which make them more attractive to humans. It is highly likely that these facial expressions do not make a dog a better pet than one that doesn't widen its eyes, but this superficial trait is still preferred over other traits, such as tail wagging," Dr Juliane Kaminski, an expert in dog cognition and study's co-author, said.

The findings have been published in Plos One.