Dawn of the smile
When my daughter was born this past August, it felt like a long wait was finally over. But soon after she came into the world — wriggling and wailing — another wait began.
Babies are born notoriously helpless. And they’re not particularly happy. Their behavioral repertoire at first skews toward the negative and the involuntary. They cry; they furrow their brows; they sneeze and hiccup and yawn. But it’s some time before they actually start to engage with the social world. It’s weeks before one day, out of the blue, they look at you and smile.
Our daughter first really smiled — unambiguously — in her sixth week. I say “really” because babies do, from day one — actually, even while in utero — form their mouths into the shape of smile. They make this face while they’re sleeping or drowsy. Adults love to interpret these so-called endogenous smiles as signs of gas or good dreams, but they’re more likely the result of fleeting brainstem activation. Chimpanzees and macaques produce these early “pseudo-smiles,” too.
You might think that a baby’s first real smiles would be tentative, a testing of the social waters. Not necessarily. Our daughter’s early social smiles — according to notes I took at the time — were big and goofy. They tended to come on fast, as if a switch had been flipped. Slowly, they became more fine-tuned. Now at four months, her smiles are on more of a smooth dimmer switch: some are subtle, others are broad and beaming. Invariably, the largest smiles we get all day are the first ones of the morning, around dawn, when she wakes up cooing and squirming, her face one big “cuddle me” beacon.
It’s no accident that we talk about smiles in terms of light. We speak of radiant smiles, incandescent smiles, high-wattage smiles. We say that someone’s smiling eyes sparkle or twinkle. There’s just something about the expression that seizes our attention and somehow warms us. When Charles Darwin described the first smiles of his own children — right around that six-week mark — he noted that, as they smiled, their eyes became “decidedly bright.”
The smile is such a powerful and primordial expression. It’s ubiquitous and universal, and so readily understood. You would be forgiven for assuming we’ve long since figured out what smiles mean and why. But the truth is — despite 150 years of research since Darwin — the origins of the smile remain swaddled in mystery.
Anatomically speaking, to smile is to pull back the corners of the mouth. This movement is a contraction of the zygomaticus major muscles, bands of muscle that run diagonally up our cheeks. The result, visually, is that tell-tale curving up of the lips. This is the essence of the smile, its sine qua non. But the simple mouth-only version of the expression often gets upgraded with contractions of another group of muscles — the orbicularis oculi. These constrict the eyes and lead to those crinkles that are sometimes called “crow’s feet.” Smiles that include the eyes like this are known as “Duchenne smiles,” after the nineteenth-century French anatomist, Guillaume Duchenne. He thought there was something more genuine at work in these cases. Such smiles “do not involve the will,” he wrote. But are “brought into play by true feeling.”
There’s little question that Duchenne smiles are more intense than simple smiles. But whether they’re actually “truer” is up for debate. In fact, the meaning of even the most basic smiles is still surprisingly contested. We all intuitively recognize a smile as a sign of happiness, of pleasure, of joy. We see those upcurved lips as telling us something about the smiler’s inner state, about how they’re feeling. This, in a nutshell, is the folk view of smiling. On this view, facial expressions are a way of broadcasting our emotions. Those curved lips — but also widened eyes, furrowed brows, and wrinkled noses — correspond to distinct inner feelings.
This account of facial expressions is not just a folk theory. It’s also a well-respected academic position, sometimes called the “basic emotions” theory. It’s most strongly associated with the work of the psychologist Paul Ekman; it has, for some time, dominated research on facial behavior. But there’s a newer theory in town, one that’s quickly gaining traction. According to this alternative, facial expressions are not about publicizing our private feelings. They’re about doing things in the social world; they’re about influencing others; they are, in short, tools of manipulation. Proponents of this “social tools” view usually reject the term “facial expression” entirely. They don’t like the metaphor it implies, that to make a face is to push out a feeling, like expressing oil from a seed. Instead, they speak of smiles, frowns, and the like as “facial displays” or “facial configurations.”
Researchers in the “social tools” camp emphasize that we smile because we want to affiliate with others, not necessarily because we’re happy. A range of studies support this interpretation. In one, psychologists — armed with binoculars — went to a local bowling alley and watched people’s faces as they bowled. If smiles are expressions of happiness, they reasoned, you’d expect a bowler to smile when they bowled well. But this is not quite what they observed. People were more likely to smile, not after rolling a good ball and still facing the pins, but moments later, once they turned around to face their friends. The same researchers also reported that people bowling alone don’t smile much at all. Similar studies have been conducted with hockey fans and Judo athletes, and all point to a similar conclusion: smiles don’t have a purely emotional motivation; they have a social one.
So, in short, the “basic emotions” view sees the meaning of a smile as “I’m happy!” The “social tools” view, by contrast, sees the meaning of a smile as “Let’s affiliate!” Now, the debate between these views is complex. It rages on, and the relevant body of research is too vast to summarize here. But, personally, I incline toward the “social tools” view. It feels intuitively right to me. And I also think it jibes better with what we know about facial displays in other species.
But before we get to those other species, first a bit more about our own. Smiling appears to be a universal human birthright. Cross-cultural research has documented this basic display in countless far-flung cultures. It’s produced by blind people and emerges in blind infants at around the same time it does in sighted infants. But, beyond this universal core, there’s some curious variability — in particular, variability in who smiles and when.
A robust literature, for instance, has found that women smile more than men. This is not an essential difference due to biological sex but rather a difference due to — as one study put it—“rules and roles.” Smiliness also varies across countries. A major predictor of this variation turns out to be the history of migration to the region. In countries with a long history of migration — places like the US and Canada — people tend to smile more than in countries with little historical migration — places like Japan or Indonesia. One reason for this could be that in a more heterogeneous society, it’s important to wield obvious signs of friendliness.
Smiliness also varies across history. In the West, we’re accustomed to putting on a toothy grin for photos. But this wasn’t always the case. At an earlier time, a big open-mouthed smile was considered unbecoming. People sitting for photos were instructed to say — not “cheese” — but “prunes” to keep their mouths small. The cultural historian Christina Kotchemidova has argued that the shift began in the 1900s, when Kodak launched a campaign to associate photography with play and pleasure. A big data analysis of yearbook photos bears this timeline out: smiling in portraits steadily increased over the course of the 20th century.
To recap: The smile is universal. It emerges early in life (whether or not you’ve ever seen a smile). It’s found across the globe (though it’s used more or less in certain places). And its meaning — whether “I’m happy” or “Let’s affiliate!” — is clearly a positive one. But a nagging question is: Why? What makes pulling back the lip corners a fundamentally friendly action? Why don’t we beam out good vibes by blinking our eyes or wrinkling our noses?
To get traction on this why question, we need to consider a close cousin of the smile: the laugh. Children start to laugh a bit later than they smile. Our daughter didn’t really laugh until she was close to 4 months old. Curiously, there was always something a little off, a little ungainly, about her first chuckles. Darwin observed the same in his own children. Laughing is a bit like walking, he ventured — it takes practice. He noted that, by comparison, “the art of screaming… [is] finely developed from the earliest days.”
If the core of the smile is a curve of the lips, the core of the laugh is a distinctive vocalization — a kind of staccato breathing pattern. Of course, these two behaviors — though different in essence — often go together and shade into each other. A grin may bloom into a laugh; a laugh may ebb into a silent smile. As one researcher put it, the two form a “continuum of intergrading signals.” A widespread interpretation of the relationship between these signals, is that a smile is a kind of diminutive laugh. The idea is even baked into the etymology of certain languages. In Latin, to laugh is ridere (which gives us “ridicule” and “risible”); to smile is subridere — to, as it were, under-laugh.
To get deeper into the why question, we also need to consider some close cousins of our species: the apes. Darwin himself observed that other primates produce their own versions of smiles and laughs. “Young orangs, when tickled, … grin and make a chuckling sound,” he observed. The same is true of young chimpanzees. He added that, when they laugh, their eyes “sparkle and grow brighter.”
A century later, in 1972, a seminal paper by the ethologist Jan Van Hooff expanded on these observations. Van Hooff argued that human smiles and laughter originated in two different primate displays. The source of the smile, he suggested, is the silent bared-teeth display, a common signal of submissiveness. Meanwhile, the source of the laugh is the relaxed open-mouth display, often known more simply as the “play face.” The play face is thought to be rooted in the mock gnawing or mock biting that accompanies physical play. Van Hooff further argued that, though drawn from these two separate sources, smiling and laughter eventually converged in humans to form a continuum of positive, affiliative displays.
A bunch of work since Van Hooff has followed up on these ideas. Much of it has zoomed in on laughter and specifically on its acoustic properties. The comparative psychologist Marina Davila-Ross, for instance, has examined laughter across the great apes. In one study, she and her colleagues systematically tickled orangutans, gorillas, chimpanzees, bonobos, and human infants and compared the vocalizations they made. What they found, through close acoustic analysis, is that each of these species has its own distinctive flavor of laughter. Humans, for instance, are the only one that primarily laughs while breathing out.
From these analyses Davila-Ross and her team built a taxonomy of primate laughter, and they found that it matches the actual primate taxonomy known from genetic analysis. Another research team followed up on these findings. They showed that human infants go through an initial stage where they laugh more like other apes, with vocalization during both exhalation and inhalation. This ape-like stage may account for the ungainliness of those first chuckles.
Additional work has broadened out beyond primates, examining laugh-like vocalizations in other mammals and even in birds. Rats, it turns out, produce repetitive ultrasonic vocalizations during play and while tickled. Kea, the parrots of New Zealand, seem to emit positive warbles that “infect” other keas. One feature that unites many of the laugh-like vocalizations found across species is that they have a repetitive quality. This is thought to mimic the heavy breathing of physical play.
So the origins of laughter are becoming clearer. To laugh is part of our primate — maybe even our mammalian — heritage, and it’s deeply rooted in play. But what has the more recent work said about the relation between laughs and smiles? Van Hooff’s original account, again, traced these two displays to different sources. The newer work has tended to favor a more parsimonious explanation. Davila-Ross argues that both displays can be traced to a single source: that primate play face. It’s an expression that does look strikingly like an open-mouthed human smile. She points out that, in chimpanzees for example, these play faces are sometimes accompanied by laughter and sometimes not, much as smiles are in humans.
Intriguingly, some infant researchers have found it useful to distinguish basic smiles, with the mouth closed, from open-mouthed smiles that more obviously resemble the primate play face. Babies tend to make these open-mouthed smiles more often during physical play. Open-mouthed smiles may have a similar shading in adults, too. An analysis in the bowling study described earlier found that people were more likely to make open-mouthed smiles while being particularly playful — for example, when hamming it up.
So, in summary, some see the smile as rooted in a display of submissiveness; others see it as fundamentally a signal of playfulness. But, importantly, these aren’t the only accounts out there. Another suggestion is that the smile has an acoustic origin: when we pull back our lips, it makes our vocalizations sound higher pitched and thus less threatening.
And so the mystery persists; questions linger. For example: If smiles are fundamentally playful, why do babies smile long before they can play? Could there be something to the fact that a smile is a fundamentally visual signal, while a laugh is a fundamentally acoustic one? And why is it that sometimes when we laugh, or experience extreme joy, we also shed tears?
The ultimate origins of the smile may remain in doubt. But its power does not. When we see a smile — in fact, even when we simply hear a smile in someone’s voice — we smile too. Baby grins are known to activate reward centers in their mothers’ brains. And these little curved mouths are not just rewarding for caregivers. Walk around with a smiling baby in your arms and people will stop in their tracks. Some of these people, in my experience, will actually thank you.
The potency of smiles can’t be an accident. A baby, again, is utterly helpless. At six weeks of age, infants are still in the so-called fourth trimester. They can’t chew. They can’t walk or crawl. They can barely hold their heads up and don’t seem to realize they have hands. And yet they wield the most powerful tool in the social world. Perhaps they needed those early smiles to solicit care and deter aggression, to protect them when they’re still at their most vulnerable.
A smile is, above all, disarming. And a baby smile especially so. Next time you get caught in the beam of one these displays — with that little curving of the lips and brightening of the eyes, maybe a playful opening of the mouth — you might feel a bit helpless yourself. And you’ll have no choice but to smile back.
– Kensy Cooperrider
Note: This post originally appeared in audio format on the ‘Many Minds’ podcast (@ManyMindsPod). You can listen to the episode here.
