evolving the smiles and frowns

Selection for Universal Facial Emotion

Alex Hilser

                With all of our faces looking so different, it is hard to imagine that humans have a similar set of facial patterns that are universal to expressing emotion. Additionally, the knowledge that not all people share similar facial muscles and that an individual can even have asymmetric muscle expressions, makes it seem even more far-fetched of an idea. But despite the assumed improbability, researchers out of Duquesne University and University of Pittsburgh have identified essential muscles present in everyone that help code for the most basic of human emotions. This helps to show the universality of emotions and how facial muscles have evolved to correspond with such feelings.

                Using 19 cadavers (7 males and 11 females, between 61 and 100 years old) the scientists went about the study by dissecting the facial muscles and categorizing the musculature. They categorized them using Table 1, which divides muscles into emotional groups. These groups are: Happiness, sadness, anger, surprise, fear, and disgust. These muscles are listed in Figure 1 and serve to show how lighter colored muscles are more universal (serve to exhibit all basic emotions), while the darker musculature is used to give each person their own complex “signature” to an emotional expression.

                In the subjects, the large determiner of basic vs. complex was their prevalence and inclination toward asymmetry. The basic subset had no variation in existence of muscles and those muscles were very unlikely asymmetrical. The complex subset, on the other hand, contained many muscles that only few people had and in many cases there were great variations in symmetrical exhibition of the musculature. The basic sub group, as per their description, had at least one type of muscle recruited for each basic emotion expressed (very universal) and it was the complex subgroups job to add the individualism because they varied from person to person (highly variable).

So how does this affect you? And how does this tie in to evolution?

                With a verification of a basic subgroup of facial musculature, that means that humans have evolved along the premise that “I feel this, I will activate this muscles”. This means that there is an innate sense of emotion and there is a very universal display at the most basic level. This is where evolution comes into play. With everyone expressing basic emotions, there has to be a way that people can express emotions that are more beneficial to mating. This means as individual variances occur to facial expressions in the population, there can be increased desire for a trait and then that musculature will only be present and developed in that lineage. This is made more complicated by the different desires of women in the human population, meaning many different types of musculature variations can find a way of being up-regulated in the gene pool. Showing how evolution has helped humans to evolve our basic subset, and natural selection has continued to shape the face of emotion.

Word Count: 488

Waller, B.M. & Cray Jr, J.J. (2008). Selection for Universal Facial Emotion. Emotion. American Psychological Association, Volume 8, pp. 435-439. DOI: 10.1037/1528-3542.8.3.435