The Science Behind Your Smile, Part 2: A Smile is Universal

So when you break it down to its basic elements, what is a smile? In technical terms, a smile is caused by the firing of cranial nerve VII which then activates the zygomaticus major (cheek raising) and orbicularis oculi (eye crinkling) muscles. There are different types of smiles, each representing different points on the emotional and psychological spectrum. We all recognize the authentic smile that you see on a child at play or on a person delighted by a birthday surprise. We also know the “buh-bye” smile of the flight attendant (made famous by a series of skits on Saturday Night Live in the 1990s) or the smile of the adult who must tolerate a neighbor’s annoying toddler.

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It took the work of Paul Ekman, perhaps the world’s expert on facial expressions, to prove that the smile is universal across all cultures [1]. In the nineteenth century, Charles Darwin was inspired by Duchenne and became the first scientist to tackle the meaning of facial expressions, dedicating a book to the subject [2]. His thesis was that expressions have a biological basis and are the same for all humans. But by the 1950s, Darwin’s ideas had fallen out of favor as the major anthropologists, such as Margaret Mead, held the belief that facial expressions were not universal, but instead were culturally conditioned. These scholars believed that people learned through cultural experience that a smile meant happy and that a grimace meant sad and none of this was hard wired. In 1965, Paul Ekman, a young psychologist studying nonverbal behavior, decided to pursue research testing the hypothesis that facial expressions were culturally conditioned. What he needed was a group of people who had virtually no contact with any other culture in the world. Ekman spoke to physician Carleton Gajdusek who was studying an unusual disease, Kuru, which was endemic in Papua New Guinea. As part of his work, Gajdusek had filmed two native tribes for over six weeks. (This same physician later won a Nobel Prize in medicine for his work on viruses such as Kuru). Ekman studied these films, observed the facial expressions of the people, and he began to think that perhaps facial expressions were more universal that he had been taught. What he needed, however, was to go and interact with these tribes to study their expressions.

In 1967, Ekman went to Papua New Guinea to live with the Fore tribe. He found a few boys who had been taught English by missionaries to serve as his translators. His first experiment was to show the tribesmen a series of photographs of people making specific facial expressions (i.e. smiling, surprise, fear, anger, etc.) and ask them to tell a story based on the facial expression. What he quickly found was that the Fore tribesmen easily recognized what the facial expressions meant, even on strange Western faces. He then turned it around and had the tribesmen read a story and choose the photo of a facial expression that expressed the story. Again they all chose the correct expression. Finally, he told simple stories (such as “His friends have come and he is happy”) to members of the tribe and asked them to make a facial expression that fit the story. Again they made the same facial expressions that our Western minds would recognize. Ekman realized that the previously accepted conclusion of sophisticated scholars — that facial expressions are culturally determined and not hard-wired — was completely wrong. And he had discovered his life work as an expert on facial expressions. Paul Ekman continues his work today at the University of California at San Francisco and has written dozens of articles and nine books dedicated to the study of emotions and facial expressions.


  1. Ekman, P., Emotions Revealed. 2003, New York: Owl Books.
  2. Darwin, C., The Expression of Emotions in Man and Animals. 1872/2002, Oxford: Oxford University Press.
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