Other than the sloth, whose smile is pretty much permanently attached, the non-human animal most associated with smiling is the bottlenose dolphin. But somewhat like the sloth, the dolphin’s smile is just a feature of the way its mouth turns up at the sides. A dolphin that appears to be smiling at you when it bobs up beside your boat might not be thinking, “Hey, let’s be friends!” even though it’s difficult for humans to interpret that delightful expression any other way.

But if dolphins aren’t smiling at us, they may be smiling at each other — or at least doing something very similar. Researchers in Italy and France found that dolphins are more likely to display an expression that looks like a human smile (what the researchers called an “open mouth facial display”) when they’re playing with other dolphins.

However, the authors point out that the expression could also be used defensively. Even when they’re playing, a dolphin’s smile might not mean what a smile means to humans.

Analyzing Animal Faces

Dogs, too, have an open-mouth expression that is very much like a human smile. But again, what’s behind the expression can be difficult to know. A group of researchers in the U.K. analyzed a variety of canine facial expressions.

They found that dogs do indeed show a variety of expressions in response to emotions. However, those expressions don’t map onto emotions in the way we might expect. In fact, the U.K. team found that dogs often display a smile when they’re afraid.

Cats, on the other hand, don’t seem to smile at all. In a now-classic comedy routine, the comedian George Carlin said cats don’t have facial expressions because they don’t have eyebrows. Some researchers beg to differ (not about the eyebrows, but about the lack of facial expressions in cats).

In research published in 2017, a team from England and Australia took software that had been developed to objectively code human facial expressions and adapted it for cats. The results showed that cats’ faces do express emotions, including fear, anger, and frustration. But, alas, no smiles.

Read More: Humans Are the Only Animals That Cry — And We Don’t Know Why

Evolution of the Smile

If you’re looking for an animal with something like a human smile, it makes sense to look at other primates. And indeed, research has shown that the open-mouth expression that apes use when playing is likely an evolutionary precursor to the human smile. But again, the expression is not always easy to read. Frans de Waal, the late primatologist and animal ethologist, described the many meanings behind primate grins. 

A smile, it seems, can mean a lot of things. Even in humans, a smile does not always convey friendliness and joy. Think of nervous smiles, insincere smiles, and smirks. There’s a fine line between a grin and a grimace. So why should we expect smiles to always signal happiness in animals?

The impulse to assume friendliness or happiness in an animal’s expression is understandable. Greg Bryant, a cognitive scientist at UCLA who studies communication and social behavior, points out that seeing smiles on animals’ faces is a bit like the phenomenon of seeing faces in the clouds. We tend to see patterns in things, and humans — social animals that we are — tend to see faces everywhere (even in toast). So naturally, it’s easy to see an upturned mouth as a smile.

Read More: Reptiles are Highly Emotional, Contrary to Their Cold Reputation

Proceed with Caution

But we should proceed with caution. Marc Bekoff, evolutionary biologist and animal ethologist, is careful about using the word smile when talking about animals.

“I don’t think they’re necessarily ‘smiling’ because they’re happy or joyous,” he says.

Take dogs, for example. Bekoff says that to interpret a dog’s expression, we need to consider the context. “Who is the dog? Who else is in the picture? Another human? Another dog? What’s happening?” A dog’s smile (open mouth, lips pulled back, tongue lapping over the teeth) usually occurs in situations when dogs are relaxed, but also occurs when they pant, Bekoff says. “A dog could be panting as a part of fear.” 

We may be doing our beloved pets a disservice by slapping a human interpretation on their smiles. “A person who doesn’t really know their dog well could make a grievous mistake about what the dog is feeling,” Bekoff says.

It might seem harmless, even kind, to treat your pets as if they’re human. But that’s probably a mistake. “A dog needs to be treated like a dog,” says Bryant. “Dogs want you to be the pack leader. They don’t want a negotiation of power. When you treat your dog like another person, it makes them uncertain about the power hierarchy, and that causes them anxiety. Trying to treat your dog in an egalitarian way can actually cause them stress.” 

So yes, animals do smile. But be careful what meaning you take from those adorable facial expressions.

Article Sources:

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Avery Hurt is a freelance science journalist. In addition to writing for Discover, she writes regularly for a variety of outlets, both print and online, including National Geographic, Science News Explores, Medscape, and WebMD. She’s the author of Bullet With Your Name on It: What You Will Probably Die From and What You Can Do About It, Clerisy Press 2007, as well as several books for young readers. Avery got her start in journalism while attending university, writing for the school newspaper and editing the student non-fiction magazine. Though she writes about all areas of science, she is particularly interested in neuroscience, the science of consciousness, and AI–interests she developed while earning a degree in philosophy.