A new study found evidence that dogs developed in physical ways to present "puppy dog eyes" as a way to help connect with humans.
The study compared the facial muscles of dogs and wolves, which share ancestral history. Dogs broke off from wolves after being domesticated about 33,000 years ago. During that time dogs changed physically and behaviorally to adapt to life with humans.
The researchers examined the heads of six dogs and two wolves for comparison. They found the facial structures of both animals were mostly very similar. But one major difference was found above the eyes. The dogs were found to have two well-formed muscles around the eye that were not present in the wolves. These small muscles permit dogs to raise their inner eyebrows, the study found.
Juliane Kaminski, a comparative psychologist from the research suggests this eyebrow-rising movement causes "a warm" feelings in humans because it makes the dogs' eyes appear larger. This expression also makes the dog look more like a human baby. The eye movement is similar to that which humans make when they are sad.
"The evidence is very obvious that dogs developed a muscle to raise the inner eyebrows after they were domesticated from wolves," Kaminski said.
In a separate part of the study, the researchers observed how 27 dogs and nine wolves interacted with a human. "We also studied dogs' and wolves' behavior. And when exposed to a human for two minutes, dogs raised their inner eyebrows more and higher than wolves," Kaminski said.
The researchers suggest that the eye movements developed over time as a way for dogs to get humans to do things for them, such as giving them food, care or attention. The only dog species in the study that did not have the muscles was the Siberian husky, which is an ancient kind of dog. The husky could be the best living example of what the link between dogs, and wolves looked like.
