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A smile is a
facial expression Facial expression is the motion and positioning of the muscles beneath the skin of the face. These movements convey the emotional state of an individual to observers and are a form of nonverbal communication. They are a primary means of conveying ...
formed primarily by flexing the
muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...
s at the sides of the
mouth A mouth also referred to as the oral is the body orifice through which many animals ingest food and animal communication#Auditory, vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also t ...
. Some smiles include a contraction of the muscles at the corner of the
eyes An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...
, an action known as a Duchenne smile. Among
human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...
s, a smile expresses delight, sociability,
happiness Happiness is a complex and multifaceted emotion that encompasses a range of positive feelings, from contentment to intense joy. It is often associated with positive life experiences, such as achieving goals, spending time with loved ones, ...
,
joy Joy is the state of being that allows one to experience feelings of intense, long-lasting happiness and contentment of life. It is closely related to, and often evoked by, well-being, success, or good fortune. Happiness, pleasure, and gratitu ...
, or
amusement Amusement is the state of experiencing humorous and entertaining events or situations while the person or animal actively maintains the experience, and is associated with enjoyment, happiness, laughter and pleasure. It is an emotion with pos ...
. It is distinct from a similar but usually involuntary expression of
anxiety Anxiety is an emotion characterised by an unpleasant state of inner wikt:turmoil, turmoil and includes feelings of dread over Anticipation, anticipated events. Anxiety is different from fear in that fear is defined as the emotional response ...
known as a grimace. Although cross-cultural studies have shown that smiling is a means of communication throughout the world, there are large differences among different cultures, religions, and societies, with some using smiles to convey confusion, embarrassment, or awkwardness.


Evolutionary background

Primatologist Signe Preuschoft traces the smile back over 30 million years of evolution to a "fear grin" stemming from monkeys and apes, who often used barely clenched teeth to portray to predators that they were harmless or to signal submission to more dominant group members. The smile may have evolved differently among species, especially among humans.


Social effects

Smiling seems to have a favorable influence upon others and makes one ''likable'' and more ''approachable''. In the social context, smiling and
laughter Laughter is a pleasant physical reaction and emotion consisting usually of rhythmical, usually audible contractions of the diaphragm and other parts of the respiratory system. It is a response to certain external or internal stimuli. Laug ...
have different functions in the order of sequence in social situations: * Smiling is sometimes a pre-laughing device and is a common pattern for paving the way to laughter; * Smiling can be used as a response to laughter.


As reinforcement and manipulation

The influence of smiling on others is not necessarily benign. It may take the form of
positive reinforcement Positive is a property of positivity and may refer to: Mathematics and science * Positive formula, a logical formula not containing negation * Positive number, a number that is greater than 0 * Plus sign, the sign "+" used to indicate a posit ...
, possibly for an underhand manipulative and abusive purpose.


Cultural differences

Researchers have found that smiling is more common in some cultures than other cultures. For example, smiles are more common the U.S. and France than in China or Japan. This pattern has been found in posed photos, such as the smiles of political leaders in official pictures and of students in school ID photos. It has also been found when researchers observed rates of smiling in everyday life. While smiling is perceived as a positive
emotion Emotions are physical and mental states brought on by neurophysiology, neurophysiological changes, variously associated with thoughts, feelings, behavior, behavioral responses, and a degree of pleasure or suffering, displeasure. There is ...
most of the time, there are many
cultures Culture ( ) is a concept that encompasses the social behavior, institutions, and Social norm, norms found in human societies, as well as the knowledge, beliefs, arts, laws, Social norm, customs, capabilities, Attitude (psychology), attitudes ...
that perceive smiling as a negative expression and consider it unwelcoming. Too much smiling can be viewed as a sign of shallowness or
dishonesty Dishonesty is acting without honesty. The term describes acts which are meant to deceive, cheat, or mislead. Dishonesty is a basic feature of most offences defined in criminal law, such as fraud, which relates to the illicit acquisition, conversi ...
. In some parts of
Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...
, people may smile when they are embarrassed or in emotional pain. Some people may smile at others to indicate a friendly greeting. A smile may be reserved for close friends and family members. Many people in the
former Soviet Union The post-Soviet states, also referred to as the former Soviet Union or the former Soviet republics, are the independent sovereign states that emerged/re-emerged from the dissolution of the Soviet Union in 1991. Prior to their independence, they ...
area consider smiling at strangers in public to be unusual and even suspicious behavior, or even a sign of stupidity. Systematic large cross-cultural study on social perception of smiling individuals documented that in some cultures a smiling individual may be perceived as less intelligent than the same non-smiling individual (and that cultural uncertainty avoidance may explain these differences). Furthermore, the same study showed that corruption at the societal level may undermine the prosocial perception of smiling—in societies with high corruption indicators, trust toward smiling individuals is reduced. There can also be gender differences. In the United States and Canada, women report men telling them to smile. For example,
Greg Rickford David Gregory Rickford (born September 24, 1967) is a Canadian politician. He is the Minister of Northern Development and Minister of Indigenous Affairs in the Executive Council of Ontario under Premier Doug Ford. He represents the Kenora� ...
, a member of the Canadian Parliament, told a female journalist to smile rather than answer the question she had asked. Biological anthropologist Helen Fisher states that, while this could be either caring or controlling behavior, such behavior is unlikely to be welcome.


Dimples

Cheek dimples are formed secondary to a bifid
zygomaticus major The zygomaticus major muscle is a muscle of the face. It arises from either zygomatic arch (cheekbone); it inserts at the corner of the mouth. It is innervated by branches of the facial nerve (cranial nerve VII). It is a muscle of facial expres ...
muscle, whose fascial strands insert into the dermis and cause a dermal tethering effect. Dimples are genetically inherited and are a dominant trait. Having bilateral dimples (dimples in both cheeks) is the most common form of cheek dimples. A rarer form is the single dimple, which occurs on one side of the face only. This bifid variation of the muscle originates as a single structure from the
zygomatic bone In the human skull, the zygomatic bone (from ), also called cheekbone or malar bone, is a paired irregular bone, situated at the upper and lateral part of the face and forming part of the lateral wall and floor of the orbit, of the temporal fos ...
. As it travels anteriorly, it then divides with a superior bundle that inserts in the typical position above the corner of the mouth. An inferior bundle inserts below the corner of the mouth. Dimples are
analogous Analogy is a comparison or correspondence between two things (or two groups of things) because of a third element that they are considered to share. In logic, it is an inference or an argument from one particular to another particular, as oppose ...
and how they form in cheeks varies from person to person. The shape of a person's face can affect the look and form as well: leptoprosopic (long and narrow) faces have long and narrow dimples, and eryprosopic (short and broad) faces have short, circular dimples. People with a mesoprosopic face are more likely to have dimples in their cheeks than any other face shape.


Duchenne smile

While conducting research on the
physiology Physiology (; ) is the science, scientific study of function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a branches of science, subdiscipline of biology, physiology focuses on how organisms, organ syst ...
of facial expressions in the mid-19th century, French neurologist Guillaume Duchenne identified two distinct types of smiles. A Duchenne smile involves contraction of both the zygomatic major muscle (which raises the corners of the mouth) and the
orbicularis oculi muscle The orbicularis oculi is a Sphincter, sphincter-like muscle in the face that closes the eyelids. It arises from the nasal part of the frontal bone, from the frontal process of the maxilla in front of the lacrimal groove, and from the anterior surf ...
(which raises the cheeks and forms crow's feet around the eyes). The Duchenne smile has been described as "smizing", as in "smiling with the eyes". An exaggerated Duchenne smile is sometimes associated with lying.


Non-Duchenne smile

A non-Duchenne smile involves only the zygomatic major muscle. According to Messenger ''et. al.'', "Research with adults initially indicated that joy was indexed by generic smiling, any smiling involving the raising of the lip corners by the zygomatic major .... More recent research suggests that smiling in which the muscle around the eye contracts, raising the cheeks high (Duchenne smiling), is uniquely associated with positive emotion." The "Pan Am smile", also known as the "
Botox Botulinum toxin, or botulinum neurotoxin (commonly called botox), is a neurotoxic protein produced by the bacterium ''Clostridium botulinum'' and related species. It prevents the release of the neurotransmitter acetylcholine from axon endi ...
smile", is the name given to a fake smile, in which only the zygomatic major muscle is voluntarily contracted to show politeness. It is named after the now-defunct airline
Pan American World Airways Pan American World Airways, originally founded as Pan American Airways and more commonly known as Pan Am, was an airline that was the principal and largest international air carrier and unofficial overseas flag carrier of the United States for ...
, whose flight attendants would always flash every passenger the same perfunctory smile. Botox was introduced for cosmetic use in 2002. Chronic use of Botox injections to deal with eye wrinkles can result in paralysis of the small muscles around the eyes, preventing the appearance of a Duchenne smile.


Other animals

In other animals, the baring of teeth is often used as a threat or warning display—known as a
snarl A snarl is a sound, often a growl or vicious utterance, often accompanied by a facial expression, where the upper lip is raised, and the nostrils widen, generally indicating hate, anger or pain. In addition to humans, other mammals including ...
—or a sign of
submission Deference (also called submission or passivity) is the condition of submitting to the espoused, legitimate influence of one's superior or superiors. Deference implies a yielding or submitting to the judgment of a recognized superior, out of re ...
. For chimpanzees, it can also be a sign of
fear Fear is an unpleasant emotion that arises in response to perception, perceived dangers or threats. Fear causes physiological and psychological changes. It may produce behavioral reactions such as mounting an aggressive response or fleeing the ...
. However, not all animal displays of teeth convey negative acts or emotions. For example,
Barbary macaque The Barbary macaque (''Macaca sylvanus''), also known as Barbary ape, is a macaque species native to the Atlas Mountains of Algeria, Tunisia and Morocco, along with a small introduced population in Gibraltar. It is the type species of the genus ' ...
s demonstrate an open mouth display as a sign of playfulness, which likely has similar roots and purposes as the human smile.


See also


References


Further reading

* * Ottenheimer, H.J. (2006). ''The anthropology of language: An introduction to linguistic anthropology.'' Belmont, CA: Thomson Wadsworh. * Cited in: Russell and Fernandez-Dols, eds. (1997). * Russell and Fernandez-Dols, eds. (1997). ''The Psychology of Facial Expression''. Cambridge. .


External links


BBC News: Scanner shows unborn babies smile
{{Authority control Facial expressions Laughter Mouth Happiness Social influence