With just the power of a pleading stare and big eyes, dogs can wrap us around their perfect little paws. It turns out that this ability is at least partly our own doing.
Recently, a team of researchers discovered that the “eyebrow” muscles that twist canine faces into adorable pleading expressions are not usually present in wolves, suggesting that they appeared after us humans, domesticated Canis familiaris.
“The movement of the raised inner eyebrows in dogs is driven by a muscle that does not consistently exist in their closest living relative, the wolf,” said Anne Burrows, an anatomist at Duquesne University at the time.
“This movement makes a dog’s eyes appear larger, giving them a childlike appearance. It could also mimic the facial movement that humans make when they are sad,” added evolutionary psychologist Bridget Waller of the University. of Portsmouth, UK.
But how we’ve changed our smart canine friends is more than superficial.
Burrows and his colleagues have since built on their eyebrow research, finding that not only do dogs have different muscles from wolves, but their facial muscle structure differs as well. Even the internal makeup of the dog’s facial muscles has changed to look suspiciously like our own.
The stained samples of the muscle around the mouth (orbicularis oris) below reveal that both dogs and humans have more fast-twitch muscle fibers (dark spots) than slow-twitch fibers (light spots), whereas it is the opposite for wolves.
As implied, fast twitch fibers react quickly – perfect for raising eyebrows or barking – but they also tire faster. Slow-twitch muscles sustain sustained movements longer, like those required for a wolf howl.
“These differences suggest that having faster muscle fibers contributes to a dog’s ability to communicate effectively with people,” mentioned Burrows. “Throughout the process of domestication, humans may have selectively bred dogs based on facial expressions similar to their own, and over time dogs’ muscles may have evolved to become ‘faster’. , further promoting communication between dogs and humans.”
Back when our bond with these animals began, back in the hunter-gatherer days of mankind up to about 40.00 years a few years ago, it was clear that rapid interspecific communication provided a survival advantage against mutual predators.
With such pressure to communicate better with humans, natural selection has also honed dogs’ ability to understand us; in some ways, perhaps even better than we can understand ourselves. To begin with, our canine companions can tell when we’re lying and instinctively sense and react to our moods.
“Dogs are unique from other mammals in their reciprocal bond with humans, which can be demonstrated by mutual gaze, something we do not observe between humans and other domesticated mammals such as horses or cats” , mentioned Burrows.
Our long shared history with these animals has created an unparalleled partnership, which has grown and thrived through millennia of change to always provide us many advantages today. During this period, dogs have also influenced our evolution – our bond is in our genes.
It is well established that humans, even at a young age, are naturally drawn to a childlike facial appearance – a set of childish traits known as the “baby schema”. These characteristics include a relatively large head compared to body size, large eyes, and a small nose – traits shared by many baby animals, including dogs and ours.
Brain scans revealed baby faces – no matter how related to us they are – hit us right in our neurophysiology. They turn on our nurturing behavior. Data from animal shelters suggests that this also applies to dogs: those with facial features with an enhanced baby pattern are more likely to be adopted.
Unfortunately, our innate fondness for the human-baby-cute has also resulted in great suffering in some of our beloved pets. While gradually warping certain breeds to shapes of our whims, over many generations we have inadvertently left them with serious medical issues.
Breeding small dogs (with larger heads) has also made some breeds more prone to heart disease. Breeding for flatter, baby-like faces has left others like pugs and bulldogs struggling to perform the most basic daily function: breathing.
You can see how much we’ve shocked some races in just over 100 years here. The good news is that now that we know how much we can shape their evolution, we can make better choices for them. We owe at least that to the dogs.
Preliminary muscle structure results were presented at the American Anatomical Association annual meeting.