Let's start with a smile. On this facial expression, there are still several discussions among scientists. Some argue that it is a completely innate behavior, others that it is a learned response, conditioning, and others that it is none of this. What we can be sure of is that smiling, and what triggers it, is innate. It’s especially linked to the sense of touch and also to kinesthetics, that is, to a form of proprioceptive sensitivity of the facial muscles. How can we assert that? We can prove it through observation. For example, picking up a newborn baby and tickling him/her, especially under the chin. At this point, the baby begins to smile, contract the lips, make very light sounds, and slightly open his/her mouth. Who has never had this experience?

All mothers know this very well: they are always the first to have these experiences with their children. In addition, the smile of the child directed to his mother is a very effective purpose of triggering maternal care and getting her attention. To tell the truth, it is also the little cry that triggers maternal care, but in this case, the maternal reactions are directed more to reassure the child than to anything else. Other causes of the smile, this time in adults, derive from gastric stimulation, that is, when we feel satiated after eating, so after a very satisfying meal. When newborns seem to smile not because they are stimulated to do so by someone, but spontaneously, it means that they do so due to the same sense of fullness after eating, even if adults, in this case, say that the children are “smiling with the angels”. They actually smile on their own, by themselves.

Adults remembering a cherished memory of a nostalgic moment do the same thing on their own. When the child gets older, a family member, primarily the mother, can trigger the causes of a smile by turning her attention to the face of the child, face-to-face as they say, while they cross gazes. This can also be triggered by a stranger: the important thing is that, when he/she stares at the face of the child, especially in the eyes, he/she emits low-intensity sounds, meaningless vocalizations. It is important that there is an exchange of intents: newborn to adult, adult to a newborn. However, after the first 3-4 months of the life of the baby, everything changes. The smile decreases and the expectations, especially of a stranger who tries to stimulate the smile of the child, are often disregarded. In fact, instead of a smile she/he could trigger the crying of the child. After this age, the child begins to be fearful of strangers.

In addition, some researchers have observed that the responses obtained with the stimulation of the infantile smile are not the same in all cultures both in intensity and in form. They can in fact be linked to the family context in which the child is born and also depend on the way in which adults take care of him/her. The child who does not grow with warmth, primarily maternal, and who are raised with indifference by other individuals smile much less and not only because he/she is not often urged to do so, but because they grasp very well the extraneousness of the situation in which they find themselves. If, for some reason, they have been traumatized by some event, they almost never smile, even when they are encouraged to do so.

Smiling is a very complex behavior and is often linked to circumstances. What can be said is that it is a fundamentally spontaneous behavior, that is, innate or, it would be better to say, hereditarily coordinated, linked to the environment and not to a form of conditioning especially of an ocular character, that is of visual contact between an adult who imitates the smile and the child. Some may raise objections to this description, but we know why this assertion is correct. How? It is enough to see the spontaneous smile, if properly stimulated, of children born deaf and blind. They smile, for example when they play or when they are urged to do so, without knowing in the slightest how a human face is made.


What happens when a triggering situation simultaneously activates different and opposing drives as in the case of conflict and frustration? In these cases, instead of smiling, the individual reacts differently: he does not smile at all, but shows his teeth and emits very strong sounds, precisely those typical of laughter and not of smiles. The aggressive component in laughter in this case gives way to a gesture of peaceful contact or rather to an attempt to diminish the effect of what could derive from a real attack. In this case, it is an almost strangulated sound, but still laughter. It turns into a gesture of submission, as we observe in monkeys when they grind their teeth (lip-smacking) in front of another individual whose threats could result in a real attack. If in these competitive situations fear increases when showing the teeth, it almost always follows the emission of characteristic sounds that are always the same and rather loud. It seems far-fetched that laughter can evolutionarily have such a meaning, but the reality is that we laugh in many circumstances precisely for these reasons even if sometimes laughter can be the result of an immediate change of mood, a cathartic effect that allows us to free ourselves from a frustrating or tensed situation.

In essence, among humans, laughter has undergone a different evolutionary path from smiling. In fact, laughter can take on an ambiguous meaning, double-faced, in the sense that it can be used, to demonstrate submission to someone, as well as to dominate someone as a sign of contempt and mockery. This is very clear in children of a certain age when they begin to play with each other. The laughter in these children takes on a connotation that is sometimes aggressive, sometimes not, or switches from one to another ambiguously.

In adults, laughter, especially the very loud and sarcastic one, can become a gesture of threat towards someone, especially an enemy or someone considered as such. In teenagers, it is very clear when one group threatens another by mocking it. This signals the aggressive unity and defense (mobbing) of one group towards another, or of an individual towards another, especially in the case in which the one who laughs is aware of his/her physical superiority, as happens in cases of bullying.


Contrary to previous beliefs about the origins of smile and laughter, it is clear that the two phenomena have little in common. They have different phylogenetic origins. To understand why we must start with how the face and the contractions of the facial muscles are used in a smile and in laughter. In laughter the mouth is completely open and rounded, the lips are retracted, and everything is accompanied by an emission of sounds that are always quite loud. In a smile, on the other hand, the mouth is not completely open, the corners of the mouth are pulled back and slightly upwards. In addition, the child's smile immediately begins to be coordinated with what is presented in front of him/her and with the ability to distinguish a friendly and usual face, such as the maternal one, from that of a stranger, something that the babies know how to do very well after 3-4 months of life. This, as already mentioned, is easy to observe in the event that an adult approaches and smiles at a child after he/she has reached this age: if the face is not known to the child, he/she immediately begins to cry, all in tune with the motivational aspects of both (adult/child). The fact that sounds are almost always emitted in laughter is not secondary. Even monkeys when they show their teeth make sounds and the extraordinary fact is that between them and the human laughing there is a remarkable evolutionary continuity, something that does not exist in the smile. In the smile, the aggressive component, if there ever was one, gave way to a pure gesture of greeting or the desire for a peaceful willingness to physical contact with others, in laughter this did not happen.

Suggested reading

Darwin, c. 1872. The expression of emotion in man and animals. Murray, London.
Van Hooff, J.A.R.A.M. 1976. A comparative approach to the phylogeny of laughter and smiling. In: Play. Its role in development and evolution. Editors: Bruner, J.S., Jolly, A., & Sylva, K., Penguin Books Ltd., London, pp.: 209-224.
Provine, R.R. 2000. Laughter: a scientific investigation. Viking Press, New York.
Ross, M.D., Owren, M.J. & Zimmermann, E. 2009. Reconstructing the evolution of laughter in Great Apes and Humans. Current Biology, 19: 1106-1111.