With those big eyes and perfect little paws, dogs hold a special place in our hearts. Our strong bond with these furry creatures started around 40,000 years ago in hunter-gatherer societies. New research from Duquesne University has explored exactly how and why we’ve chosen to transform ferocious wolves into adorable companions. The findings were reported at the annual American Association for Anatomy meeting.

Dogs’ “eyebrow” muscles are what allow them to contort their faces into pleading adorable expressions. Interestingly, these are not present in wolves, meaning humans have selectively bred for this trait when domesticating these wild animals.

“This movement makes a dog’s eyes appear larger, giving them a childlike appearance. It could also mimic the facial movement humans make when they’re sad,” explained evolutionary psychologist Bridget Waller.

Researchers conducted composition research comparing dog, wolf, and human facial muscles. They found that a variety of muscles all over dogs’ faces were drastically different from those of wolves, although were strikingly similar to a human’s muscular face structure.

Analysis of mouth muscles, called orbicularis oris, revealed an abundance of fast-twitch muscle fibers in dogs and humans. These fibers respond quickly, making them perfect for barking and raising eyebrows, although they fatigue speedily. On the other hand, wolf mouths are composed of slow-twitch muscle fibers, perfect for sustaining longer movements for howling.

“These differences suggest that having faster muscle fibers contributes to a dog’s ability to communicate effectively with people,” said Anne Burrows, lead author of this study. “Throughout the domestication process, humans may have bred dogs selectively based on facial expressions that were similar to their own, and over time dog muscles could have evolved to become ‘faster,’ further benefiting communication between dogs and humans.”

Better communication between the species created a mutual survival advantage from predators and catching prey. This evolutionary relationship was extremely successful, causing a deep inter-species understanding to form. In some ways, dogs can understand us better than we can ourselves, with studies showing they can tell when we’re lying and sense and react to our moods.

Knowing this helps explain the reasons why we have driven canine evolution down this particular path. Overbreeding in some species is a huge issue that has unfortunately caused joint and breathing problems in our furry friends. Being aware of how powerful our choices are in this regard can help breeders make better future decisions for healthier dogs rather than “cuter” ones.