The smile is an innate and universal behavior; it is defined by the elevation of the mouth‟s extremities, a movement produced by the zygomatic major muscle. A smile is an expression of positive emotions, but it can also be used to hide negative feelings, prevailing here its social nature. A genuine smile is characterized by the joint action of the zygomatic major and orbicularis oculi, which raises the lower eyelid and causes wrinkles on the outer corner of the eye. The universality of the smile admits differences caused by factors such as culture, gender and age, which regulate the frequency and intensity of the smile‟s occurence. In the phylogenetic path, smile evolves from silent bared-teeth. Both play a role of appeasement, emotional bonding and social cohesion. However, human beings have the ability to control and adjust the smile to social situations. The smile is a constant presence on the human being‟s ontogenetic path; initially spontaneous and a reflex, it evolved into a social and instrumental behavior. Laughter, coming from primate‟s play face, is the most intense phase of a muscular process similar to the smile. However, laughter has an extroverted nature which manifests itself through vocalization, and fulfills a social function only. The mouth is the most dynamic element of the face, and the beauty of the smile results from facial harmony and the balance between the teeth and soft tissue. Art expresses a wide range of human emotions. The archaic smile and the smiling face of gothic sculptures consist of an artistic convention. The Baroque presents a wide range of smiles, being probably the most significant art movement regarding the presence of the smile. The ambiguous expression of Mona Lisa reveals the power of the human smile. A closed smile, faded by sfumato, is only perceptible through peripheral vision

Tese de mestrado, Anatomia artística, Universidade de Lisboa, Faculdade de Belas Artes, 2012