A Strange Detail About Dogs’ Eyebrows Is Leaving Pet Owners A Bit Uneasy

When it comes to their evolutionary history, dogs remain somewhat mysterious to us. There are plenty of theories out there about how they ended up the way they did, but nobody really knows for sure. For experts concerned with this question, there’s plenty to debate and try to learn about.

Dogs are quite an unusual species, all things considered. There are very few others capable of having members so wildly different in terms of their characteristics, while still being able to breed with one another. Just think about a German shepherd standing beside a pug — the differences speak for themselves.

Dog evolution is a fascinating subject. Even Charles Darwin gave it a great deal of thought, though it turns out he got some things wrong. He was under the impression dogs were the culmination of many different wild canines mating and passing on their traits. But contemporary science tells us quite a different story.

According to more recent research, it seems we can trace dogs back to an animal that lived something like 60 million years ago. That would place us in the geological epoch known as the Paleocene, which began after the big extinction event that wiped out the dinosaurs. This dog ancestor was called the Miacis.

With its long, slinky body, it’s probably fair to suggest the Miacis looked, if anything, more like a weasel than a modern dog. Its legs weren’t proportionately as long as those of most dogs today, plus its brain wasn’t as big either. It did have similar kinds of teeth, though.

Fast-forward about 35 million years, and we find ourselves in the Oligocene epoch. This is when a creature known as the Leptocyon was scampering around, which was maybe a little more recognizably like a dog. It could probably be argued, though, that it looked quite a bit more like one of today’s foxes.

Down the line we have an animal called the Mesocyon, which was around something like 20 million years back. This creature definitely looked more like a dog, and its brain was bigger than the ones belonging to its ancestors. This grey matter was better equipped to remember things, which likely helped the animal to recall the members of its own family. This, then, would have laid the groundwork for the development of a pack mentality.

Somewhere between 5 and 7 million years back, we finally see wolves enter the picture. These animals were really effective hunters, displaying an ability to successfully pursue and capture prey. Over time — taking us to about 1 million years ago — they evolved into the version of wolves we’d recognize today.

The hunting abilities of wolves are legendary — literally. A whole host of myths exists about wolves within human culture, and that’s as true now as it ever was. We’ve all seen a movie or read a book about a werewolf. For whatever reason, wolves really seem to capture our imagination.

Maybe wolves fascinate us so much because of their intrinsic connection to our own species’ best friends. Dogs descend from wolves — and both species still exhibit some of the same features. These similarities have their limits, though, as dogs have changed a great deal compared to their wild ancestors.

But how did these changes come about? Well, that’s up for debate. One theory says wolves realized human communities could provide them with food. Over time, the argument runs, they spent more and more time within the vicinity of people, gradually becoming more comfortable in their presence.

The process could have worked both ways. As wolves became more comfortable with humans, we started to see a use for them, too. People may have enlisted wolves’ help to react to approaching danger. Eventually, the animals were trained and used in hunts. It’s possible they could even have provided us with warmth.

Incredibly, some experts think this process of wolf domestication happened more than once. In other words, the consequential development where wolves gradually adapted their ways to become friends with humans happened in different places at different times, totally independently of one another. If true, it lends the story an air of inevitability.

Even today, dog trainers keep the behavior of wolves in mind as they set programs for people’s pets. But at the same time, dogs have changed quite a bit since their days out in the wild. You can’t just treat them totally like wolves and expect them to respond appropriately.

Plus, the level of variation seen in dogs today is immense: what works for one breed might not work for another. But how is it that a species can contain members with such different characteristics? What happened during the course of dog evolutionary history that led to all the breeds we know and love nowadays?

Well, responsibility for that basically falls at our feet. Through a process of artificial selection, human beings have changed the course of dogs’ evolutionary history. Our species is responsible for breeding dogs, which encourages certain traits to be passed along and not others. That’s why we have so many different kinds of pup.

For thousands and thousands of years, humans have been drawn to dogs like no other animal. And that’s had a direct impact on the ways in which they’ve evolved. But what is it about dogs that have always drawn people in? Well, a researcher named Juliane Kaminski has a theory about that.

Dr. Kaminski and a team of colleagues from Duke University in Durham, North Carolina, have undertaken a study on the famous “puppy-dog” look of our pooches. You know the one: the stare that turns people to mush and makes them fuss over the dog. Well, why does that look have such an effect on us?

Well, the researchers seem to think it has to do with the fact the puppy-dog face looks a little like the expression people wear when they’re upset. When a person sees another person looking this way, it makes them feel as though they want to nurture the upset party. Maybe a similar response is at play when we see dogs wearing it?

But if dogs can make a face that elicits a nurturing response from us, then surely wolves can too? Well, not so much. The researchers studied both animals and found that dogs had a special muscle which raised their eyebrows, thus helping them to make the face. Wolves, on the other hand, didn’t.

Without this muscle — which, incidentally, is known as the “levator anguli oculi medialis” — wolves can’t make the cute puppy-dog face anywhere near as effectively as their more domesticated cousins. And the researchers actually studied them both to check. Sure enough, they found dogs moving their eyebrows and looking adorable far more often than their wild counterparts.

None of this is particularly surprising, though. Most of us, after all, have been taken in by the puppy-dog look personally, so on some level we already knew it affected us in an intense way. But it gets interesting when the researchers point out what the implications of all this are.

Another group of researchers from the University of Sydney have done some work at a dog pound. Basically, they were analyzing which dogs tended to get adopted from the facility after people paid the place a visit. The findings were stark: the animals with the most infant-like features tended to be favored.

There’s a fancy word that’s worth knowing when getting to grips with all this. It’s “paedomorphism,” which basically just refers to a living thing holding onto juvenile traits even in maturity. In this case, dogs with more paedomorphic characteristics appealed to humans more than animals who looked more mature.

What can be drawn from the two pieces of research? On the one hand, we have some experts claiming dogs have a special eyebrow muscle that helps them look young and cute. Whereas on the other, we have a study saying humans are drawn to young-looking dogs. That can’t be a coincidence.

Laying out their thoughts on this potential link, Dr. Kaminski and her many colleagues wrote, “One hypothesis suggests that wolves underwent a process of self-domestication as tamer individuals took advantage of opportunities to scavenge from human settlements during the agricultural revolution.” The paper noted that evidence had been uncovered in recent times which suggested domesticated canines had genetically evolved to cope better with a diet high in starch.

The group goes on, “During domestication, dogs have departed from wolves on various other behavioral and physical dimensions, one of the most striking being paedomorphism. In many ways dogs appear more like wolf puppies than wolf adults. These features are thought to have evolved as a byproduct of the domestication process, and arose accidentally when aggression was actively selected against.”

So, breaking through the academic tone of those passages, what are the researchers actually saying? Well, speaking broadly, their basic point is that dogs have held onto those traits that make them seem young because that’s what humans like. We then breed dogs in pursuit of animals with those very characteristics.

Of course, the eyebrow muscle responsible for the puppy-dog face isn’t the only paedomorphic trait in dogs. Far from it, in fact. The shape and size of their skulls, for instance, have been described as infant-like, as have their shorter noses and tails compared to those of wolves.

Accentuating the eyes and making them seem big is a very striking paedomorphic trait, as it, in some way, makes humans think of their own young. Babies have big round eyes, so seeing something similar in animals might make us feel protective towards them. You even see teddy-bear manufacturers take advantage of that tendency in us.

Paedomorphic traits don’t necessarily have to be physical, though. Aspects of animals’ behavior might also be considered infant-like, traits which are very clear to see in dogs. They are, after all, very fond of playing, even well into maturity. They also bark more than their wild predecessors. You might say they never fully stop being puppies.

Given the sheer variety of dog breeds around, though, not all exhibit infant-like traits to the same degree as others. There are some pooches, after all, that have held onto a lot of the same characteristics we can see in grown-up wolves. These are the lupine breeds, which include samoyeds and huskies.

Where paedomorphism is most evident in dogs is definitely within toy breeds, such as the Pekingese, the shih tzu, and the Cavalier King Charles spaniel. With their short noses and round heads, these pups can be cited as a pretty extreme example of animals defined by very clear infant-like qualities.

If you’re not convinced by the theory, let’s just think about what those supposed paedomorphic characteristics seen in toy breeds are. First, the animals are soft to the touch. On top of that, they’re very small — and they’re not exactly independent. Their owners even tend to handle them as they would an infant, picking them up and holding them.

In addition to all that, there are more subtle babyish traits in toy breeds. Some even have eyes that seem to tear up, which is something we might associate with our own young. Even the curly tail a lot of these dogs have is similar to what you’d see in a baby wolf.

It can feel a little weird to think dogs’ development has taken such a dramatic turn, all because of us. Just because human beings like it when dogs look and act like baby wolves, a whole host of toy breeds have come into being. Morality aside, it’s certainly a strange evolutionary development. Remember that the next time your pooch pulls the puppy-dog look.

Of course, it’s not just dogs that exhibit paedomorphic traits that capture our attention. Cats are probably the other notable example, as one piece of research has suggested the purring sound they make evolved to appeal to us. It apparently somewhat resembles the sound of a human baby crying, so naturally it tends to cut through with us.

So, if these researchers are to be believed, it seems human beings can be pretty easily manipulated into liking certain animals. All they need to do is act really quite juvenile. Do that, and we’ll be putty in their paws. In some ways, that really means they’re the ones in charge!

Still, there are limits to this argument. It’s not as though the only reason humans like dogs is because they act like baby wolves. Like us, they’re complicated animals, and there’s a lot going on with them. But maybe this research just sheds a bit of light on the relationship between humans and man’s best friend?