Sucking is amongst the first actions performed in our life. Already in the womb, the foetus starts to practice to suck her thumb. Some suggest that early signs of lateralization can be related to the preference toward the right or left thumb. Minutes after the birth the newborn seeks the mother nipples to suck, at this stage the sucking movement seems to me mostly a lip action with little participation from the jaws; even if the action as in most infant activity seems to travel through her whole body.
The sucking action can be stimulated by the touch of a finger on the cheek, what probably simulates the nipple presence, however as sucking in the womb starts without any external action I think of sucking in newborns as a “voluntary” action.
The novelties present in the after birth action are the arrival of the milk in the mouth and stomach of the baby, what reinforces the comforting nature of sucking, and satisfy a primary need of the newborn and the contact with the mother. Without considering all the aspects of breastfeeding, let’s focus on the end of the feeding when the baby “let go” of his head and shows an expression of intense satisfaction.
Is this expression a smile? If so, is it different from the social smile, seen later on in child development?
This expression is in my opinion different, despite the similarities, from the social smile. Duchenne pioneered the investigation of the muscular pattern leading to express specific emotions in men and identified as an essential feature of an authentic enjoyment smile the simultaneous symmetric contraction of the zigomatic and orbicularis muscles. Darwin in his “Expression of Emotions in Men and Animals” recognized the orbicularis contraction as a key ingredient of a smile, what gives us crow’s feet, and proposed that the social smile initiated as a suppressed aggressive gesture, due mostly to the teeth exhibition, however this suggestion does not seem supported by adequate evidence, even if it is difficult to completely reject it.
As in most human activity several complex layers are present, cultural differences can explain the observed variation of the smile frequency amongst different populations and genders, concealed emotions ranging from contempt to flirtatious feelings are accompanied with different types of smiles as pointed out by P. Ekman. The distinction between artificial and felt smile is in a certain way artificial as all of the smiles types express different emotions and it is only our limited attention to the person smiling that limits our ability to discern the emotions behind. In this sense the expression of the newborn after feeding is a “Buddha” smile, it is aggression free and free from any social pressure, it is an inner smile, the baby is pure joy in that moment and she lets us know through a wonderful expression.