A new study reveals the science behind those sweet viewers. And it turns out that we bred that irresistible look ourselves.

Can’t resist your dog’s admiring expression when he begs for a treat? A new study reveals key anatomical features that could explain what makes your dog’s face so attractive. And the findings may surprise you. Because dogs didn’t invent the ‘puppy eyes’ themselves. In fact, we ourselves are to blame.

Puppy eyes

Anyone who owns or has owned a dog knows what it is: puppy eyes. The eyebrows are raised, making the eyes appear larger and more childlike. And who can resist that look? Putting on those cute eyes does indeed pay off. Those irresistible puppy eyes instill a strong desire in people to take care of them and… give in.

extra muscle

In a previous study by the same researchers, they already revealed that dogs – unlike wolves – have an extra muscle above the eyes. This muscle allows them to raise their eyebrows and set up puppy eyes. In the new study, the researchers go a step further. Because that sweet look of our four-legged friend, it does something to us. So it seems that dogs have found a way to communicate in a “human-like” way. But how did that come about?

Anatomy

The new study focuses on the anatomy of small muscles used to form facial expressions. These muscles are also called ‘mimetic muscles’. “All mammals we know have mimetic muscles,” researcher Anne Burrows told Scientias.nl from. “These partly consist of fast-moving fibres, the so-called ‘fast twitch fibres’. The fast twitch fibers contract quickly, but also tire quickly. This is why we can’t smile for a long time during family photos. We also have ‘slow twitch fibres’. These contract slowly, but are resistant to fatigue.”

Study

The researchers compared the different fibers in the faces of both wolves and domestic dogs; two species that are closely related. Although the exact timing is unclear, scientists estimate that wolves and dogs were genetically separated about 33,000 years ago. That’s also when humans started to selectively breed wolves; the first species ever domesticated.

facial expressions

Research into their mimetic muscles yields an interesting insight. The results show that dogs have more fast twitch fiber than wolves. Having more fast twitch fibers makes the face more ‘flexible’, thus allowing them to form facial expressions. In addition, they allow for quick, but small movements, such as raising the eyebrows – hello puppy eyes. And this just might be the reason dogs are so good at communicating with humans. “People can make facial expressions at lightning speed,” Burrows says. “That’s partly due to the dominance of fast twitch fibers. Because dogs have a lot of those too, they can communicate with us in a way that is similar to how our own muscles contract. Essentially, dogs almost ‘mirror’ human facial expressions.”

The face of a wild gray wolf, a domestic Golden Retriever and a human. Below you see the corresponding tissue samples from the oral sphincter. In the photos, the human and dog are both actively using this muscle (note the dog’s raised lip, which mimics a smile). Also, the tissue samples reveal many similarities between dogs and humans that likely contribute to facial flexibility compared to wolves. Image: Anne Burrows, Duquesne University

domestication

The fact that dogs only started to have more fast twitch fibers after they separated from wolves means that humans must have been involved in this process, according to the researchers. In fact, Burrows suspects that humans contributed to dogs’ ability to shape facial expressions through thousands of years of selective breeding. “During the domestication process, people may have bred dogs based on facial expressions similar to their own,” she explains. “Over time, dogs’ mimetic muscles have evolved, giving them more fast twitch fibers, further enhancing communication between dogs and humans.” Incidentally, according to Burrows, it is unlikely that people from the Paleolithic era consciously bred for this. “I think they just kept dogs around longer with pleasant facial expressions,” she says.

Deeper insight

The findings from the study provide a deeper understanding of the role facial expressions play in human-dog communication. It somewhat explains why dogs—unlike other mammals—are able to bond with humans and reciprocate our gaze. “This is something we don’t see between humans and other domestic mammals, such as horses and cats,” Burrows said. “That probably has to do with the fact that we’ve been dealing with dogs for over 30,000 years; much longer than with other domestic animals such as the goat (domesticated about 8,000 years ago) and the cat (also 8,000 years ago). It is clear that people have not domesticated dogs to eat them, but rather to hang out together.”

Overall, the study suggests that having lots of fast muscle fibers may have contributed to dogs’ ability to communicate effectively with humans. But not only that. “Perhaps the most important implication is that it gives us insight into what early humans, who lived about 40,000 years ago, valued,” says Burrows. “They wanted a dog that would be a companion to them and help them with various tasks, such as hunting. It also tells us that there is a lot going on in our human-dog bond that we may not be aware of when we stare into our dog’s eyes. Dogs are here to be our companions, communicate with us and support us. We should be the same buddy for our dogs!”