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Why do we smile?

Student's picture


Smiles are generally accepted as a universal facial expression of happiness or joy. We get instincts about which smiles are more genuine, are more felt than others, and which are more forced and more politely construed. I wanted to find out whether smiles are a social reaction- something learned amongst society- or whether there’s an actual biological reason why, when we are given a positive stimulus, our cheeks bulge and the corners of our mouths turn upward. I started with the understanding that because it would be difficult or impossible to define happiness on an individual level, which I am taking to be the stimuli of the smiles themselves, the results would have to be more generalized and the findings would probably be somewhat controversial and less conclusive. I proposed that smiling was more directly linked to a physical, neurobiological response than to social interactions, because I assumed that there had to be some reason why even the most creative and brilliant of thinkers followed the rest and smiled to show pleasure.

For this paper, I chose to define happiness or pleasure as something we instinctually, consciously think we enjoy. I read that there are different types of smiles, which are often grouped into two categories, “Duchenne smiles”, and “Pan American smiles” (1). The “Duchenne smile”, named after researcher Guillaume Duchenne, involves the movement of the zygomaticus major muscle near the mouth, and the orbicularis oculi muscle near the eyes. It is believed that this smile can only be produced as a result of genuine positive emotion, making it involuntary. By contrary, the “Pan American smile” involves only the zygomaticus muscle, and is entirely voluntary, being used more often used to show politeness or mask true emotion (2). This suggests a partial control we have over the kind of smile we show when it comes to realizing that we need to put a smile on our faces for social approval, but little control over smiling about things that genuinely make us happy.

Stroke victims help us understand more of the distinctions between these two types of smiles. When they have had damage to their motor cortex, they often cannot physically concoct their faces into smiles voluntarily, but can smile Duchenne, involuntary smiles, when given a positive stimulus (3). Those having more damage to the deeper-seated basal ganglia can smile on command, but can’t smile as an involuntary reaction, for example, when they hear something they find funny (4). This shows a difference in the roles of different muscles and neurons when it comes to the different types of smiling, suggesting a correlation between not being able smile voluntarily with injury to the motor cortex, and not being able to smile spontaneously with injury to the basal ganglia. The latter is often seen in Parkinson’s disease patients, in whom the basal ganglia degenerate, and there becomes impairment to voluntary movement, with much loss of involuntary movement, including tics, as well (5).

While this shows that different parts of the brain and different brain messengers control different functions, I wanted to combine that with the social factor of smiling in an attempt to put it all together to determine how smiles work. Many studies have indicated that smiling is an innate reaction (1), most often due to happiness. This claim has been made as a result of several factors, including being based on studies of fetuses and children at young ages.

Since 2001, a four-dimensional scanner has been used to allow doctors to see that babies in the womb exhibit facial expressions (6). With the corners of the mouth turned up and the cheeks bulging, obstetrician Stuart Campbell, who’s in charge of this new discovery, says, “what’s behind the smile, of course, I can’t say, but… I think it must be some indication of contentment in a stress-free environment” (6). The 4D scanner, which also produces 3D images that move in real time, shows that babies start making finger movements at 15 weeks, yawning at 18 weeks, and smiling, blinking, and crying at 26 weeks. After birth, infants do not usually smile until they are 6 weeks old, creating a further interest to survey the womb and why there is this gap of time where no smiling occurs, perhaps because the infant must adjust to its new, less content surroundings. This new information on the subject suggests that perhaps smiling is a reflex to positive feelings, while at the same time can also be a response to hearing social communications from inside the womb.

Another interesting study was done on feral children who live in isolation from human contact and have remained unaware of human social behavior and unexposed to language (7). While there having only been just over a hundred reported cases, these children generally do not smile (1). Isolated from human interaction, they lend an interesting view to the question of why we smile. Since there are so few that are feral, placing great emphasis on this may not be the most constructive, but it is important to keep in mind when assessing how much social interaction plays in the role of a smile. Instead of the six week gap for these children relearning or regaining the confidence to smile after leaving the womb, they never do, and that’s really interesting. It highly suggests that social interaction plays a large role in either smiling as a reflex, or helping to biologically develop the brain to be able to be able to pick up this kind stimuli reflex.

While researching, I realized that both my questions and assumptions were broad and generalized, and while being wrong is far more constructive, I think this question of why we smile, in addition, is still greatly under observation and study. While there’s a connection between different parts of the brain and creating the two very different types of smiles, the connection between the physical brain functions and the social aspect of smiling seems harder to categorize and distinguish. I think that perception has been an underplayed role in these studies, as it is perception that allows us to see things in terms of positive or negative, but more specifically in the kind of positive or negative our brains group our reactions into. I think we all react differently, as we all analyze situations differently, and the connections between the social realities, our perceptions, and the point at which we smile are all very far from each other. As far as story-telling goes, I like the story of the fetus smiling, and of the feral children not having this reaction. I like these stories, because they partially contradict one another- these feral children were once fetuses, and potentially could have smiled, which means they had some influence- whether it was a reflex, a biological condition, or something socially enhanced- that made them smile. The thing that was lost over time for them- that separates them from a more typical child that matures amongst others- is what I’m interested in to find out. If they walk outside one day, or see something visually stimulating to them, it troubles me that their reaction isn’t to smile- that they must have some other way of communicating happiness, as I’m choosing (and in this, assuming), not to believe that humans can be nearly completely difference species amongst the race with an inability to communicate how they feel in way most other humans can easily acknowledge. This is similar to a problem we discussed earlier in this class- if there was a life on another planet that was so vastly different from life on Earth, would we be able to identify it?

My initial hypothesis, that smiling was more neurobiologically based than as a response to social reactions, I found unable to either prove or disprove. I realized that my story on smiling was too general, and that I was looking for concrete information when that’s not the way science, or biology, or anything really, works, or should work. I think it’s interesting that the vast majority of the population smiles, yet we’re not really sure why. I think the assumptions made on the act of smiling, including having to assign a definition to happiness and positive emotions, is probably a big cause of discrepancies, since everyone is so individualistic and it’s hard to describe exactly what kind of positive emotions we’re feeling, and tying it to the facial expressions, possibly a smiles, on our faces at that time. I think that smiling is the result of both social responses and of physical brain controls and functions, probably combined with other factors such as non-living environmental ones. I also realized that I proposed my hypothesis with the assumption that neurobiological functions and social reactions were in two opposite categories when in fact it’s likely that they are linked, as all social interactions are processed in the brain. It’s interesting to think about things, such as smiling, we’ve grown up being able to recognize and identify, but not really knowing why things are the way we’ve learned them to be.


Works Cited


Craig's picture

Why smile?

I think smiling is a non verbal way of showing feelings of pleasure ("I like"). Directing at others, tells them that we are friend, not foe. All species "smile" (showing "pleasure" or "non-pleasure"). The opposite says that we can be dangerous, hostile and aggressive (a threat to our well-being). When smiling, we say we are pleased to see and relate to the person (OR NOT!!!), letting them know whether or not we see them as "likable". We therefore "like" what we see and hear. We can and often do add other non-verbal messages to a smile. With the smile, we can say "I like relating with you, want to be with you, I mean you no harm", etc, or, "I like what I see, and want to abuse/eat you", etc. We can often consciously or unconsciously detect what those non-verbal messages are, with the smile that says... "I like".

Sharen's picture

Has anyone studied persons

Has anyone studied persons born blind, so without the ability to see what others do when made happy?

fatema's picture

reason 4 blind people's smile

i would like to share a thought by answeing your question, as to why blind people smile, when they cannot view social behaviour or social interactions which would make them its not just the eyes which contribute to your smile,but there are rest four sense organs which can make you smile,for ex:when u listen to a good music, you feel happy,and experience pleasure that makes you happy.similarly if u smell good food and you are pleased by it,you feel happy and you smile..........

Don Layton's picture

Why do we smile

Grand Unified Theory of Smiling

We will start with being tickled. We have some areas on our bodies that are more sensitive than others. They are there so we can sense being touched and react quickly. Humans, not having the ability to push off with front legs to get moving fast, move our arms. In order to move we exhale, that help speed our moving.
Any time we are surprised, we move. We move a lot when we hear a funny joke. we move when we see someone we like. We move when we are happy.
I beleive we can prove this by having an audience hold on to a horizonal bar, just below chest high. And having a comedian tell jokes to them.
And then have them listen without the bar.
I beleive they will laugh more without the bar!
While we are exhaling, to control the output of air our vocal chords cycle on and off. That makes a sound like laughing. To insure the air can get out we open our mouth. Opening your mouth by lowering the jaw takes more energy, so we open our mouth sideways, that looks like a smile.
Anytime we do deep breathing exercise,, we feel better because of the extra oxygen we get.
So it means if we laugh, we get more oxygen.
So the reason we smile is to let air out. Which does not take away the value of a smile, because when you see someone and they smile at you, you will know they are tickled to see you!

anonymus's picture

thank you

thanks for writing this it really helped me with the project that i'm doing!!

kanoameha's picture


An important data point to consider:

The emotional expressions of blind people (blind from birth) are identical to those that are not blind. Smiling spans all cultures, all societies, all ages, and all races. One who has never "seen" a smile still expresses their joy through a smile.

So, if a ferel child cannot smile, or does not smile, perhaps it is tied to the lack of "joy" being present. Add the fact that they never "saw" a smile (mirror neurons) during this ferel time period and it is no suprise to me that even when we smile at them now, they do not smile back. This does not negate the fact that smiling is hardwired. At its core level, it is not a learned behavior.

I suppose all ferel children, aside from the brain damaged ones, would eventually smile once they experienced joy. In almost all of the ferel cases they have been abused and their world was predominately led by fear. In some of the others they were abandoned, or raised by animals, and so only very basic emotions (of the environment they mirrored) would be activated.

Gerald T. Regan's picture

Length of upper mouth wall

Prescinding from the feral individuals, there is a place for a study of the distance from the center of the nose between the two nostrils and the upper rim of the aperture of the mouth. The conjecture is that if this distance is long, the individual will smile only with difficulty. If the idea holds up, one genetic factor will be revealed. Run with this ball, someone.

Vix's picture

Never SMILE in a photo

Found this article when looking for material for a photography lesson on portraits. I am trying to explain to a student why you should never ask subjects to "Smile!". . . this helps a lot!

haroon rashid's picture

hi i like karens hypothasis

hi i like karens hypothasis as to why humans smile. im reasearching a topic at the momment, and i belive that we learn to smile in relation to our teeth.

although humans have canine teeth by nature humans are herbivores but have the ability to eat meat hence humans are classed as ominvores. However human canine teeth have evolved not for hunting and eating meat but as a defensive or attacking mechanism. humans like all other apes used thier teeth to bite thier opponets if they were attacked or to impose themselves with in a certain social order of thier group.

The way we expose our teeth shows others within our group if we are happy and trusting,( we are approchable and not dangerous)' hence we smile, also when we are angry or aggressive we fully expose our canine teeth to our agetator.

young human children especially boys go through a bitting phase of life, bitting older brothers or sisters or freinds as they try to get thier way.

Mike Tyson bitting his opponents ear is the classic example of this kind of behaviour.

Even those fernal children who did not smile ad a submissive and approchable. or an aggresive method of exposing thier teeth.

Humans are not the only animals that smile, our fellow Great Apes all smile and laugh and show aggression in a similar fashion to humans. Cats and dogs,and other animals with teeth or tusks all have a method of exposing their teeth, to show passive and aggressive intentions.

the way we smile also exposes our teeth to the opposit sex, if we have good and heathy teeth the broader our smile.the first time we meet a sranger we smile to show that we are not aggressive. humans even smile when we greet our non human pets and animals.

We smile to expose our teeth, to show we are not a threat or danger, to others.

Serendip Visitor's picture

and when I want to put

and when I want to put someone at ease, I show them my knife, just to assure them that I wont use it.

Anonymous's picture

hey this really explains why

hey this really explains why i smile alot.Im always happy for some reason.