Dogs may have evolved to capitalize on our preference for big-eyed, child-like faces, according to new research.

When man's best friend raises its inner brows, it makes the eyes appear larger — like those of a baby — a look that prospective dog adopters respond to.

Scientists at the University of Portsmouth observed 27 shelter dogs and counted the number of times each animal raised its inner brows and widened its eyes when a person approached.

The dogs were all Staffordshire bull terriers and Mastiffs between the ages of 7 months and 8 years old, and the ones that raised their brows were consistently adopted faster than those that didn't.

Head researcher Dr. Bridget Waller says this is evidence that domestic dogs have evolved to make these "puppy dog eyes."

"The results of this research suggest that wolves which produced child-like expressions may have been more tolerated by humans, and so modern dogs have inherited these features," she said.

"We might have automatically opted for dogs which produced facial movements that enhanced their baby-like faces. Raised inner brows are also closely associated with sadness in humans and so another possibility is that humans are responding to a perceived sadness in the dog."

Study co-author Juliane Kaminski said that we know very little about the early domestication of wolves and it’s likely that humans had a preference for animals with faces that reminded us of our own.

"It is clear that specific physical features were actively selected for as wolves were domesticated to become dogs, but other features may have also been selected for unconsciously," she said.

Previous research suggested that the domestication of wolves was simply a byproduct of people avoiding aggressive animals.

However, this new study indicates that dogs' child-like expressions are a result of indirect selection by humans.

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