(CNN) – Every dog owner has been there; brought to your knees by your favorite canine’s “puppy dog” eyes.
Well, a study published Monday says evolution may be behind that famous facial expression.
According to researchers, a specific muscle causes dogs’ inner-eyebrow to raise and that makes their eyes appear bigger and more infant-like.
The scientists believe dogs do it specifically to get a reaction out of humans.
Researchers say canines adapted the expression as they became domesticated over 33,000 years ago.