Dartmouth professors Paul Whalen and Robert Kleck reviewed a study that investigated the adaptive purpose of various facial expressions in a recent Nature article.
“Are the configurations on your face random or are they there for a reason?” Whalen said in an interview with the DUJS. “Evolution is random, but these things that come about randomly, and stick around through natural selection, stay because they serve a purpose.”
The article discussed a study by J.M. Susskind and others at the University of Toronto, Canada, that was published in Nature Neuroscience. The research demonstrates that facial expressions of fear work to enhance sensory perception.
In the study, subjects made fearful and disgusted faces and their ability to intake sensory information was measured under both conditions. With each of these facial expressions, the face moves in opposite ways, in terms of a raised or lowered brow, widened or narrowed eyes, and an open or closed mouth. These opposite facial movements result in an opposite effect on sensory intake. While sensory perception was heightened with fearful expressions, it was decreased when subjects made disgusted faces.
Ability to intake sensory information was measured in several ways. Subjects were tested on their ability to detect quick flashes of light in their peripheral vision and to move their eyes to targets in their visual field. Researchers also measured the amount of air the subjects inhaled through their noses.
When subjects posed fearful expressions, their visual field became larger, their eye movements were more rapid, and the amount of air inspired through the nose increased. The opposite effects were seen with disgusted expressions.
Whalen cautioned against making definitive conclusions from the article in terms of the origin of facial expressions.
“There are multiples reasons for why fear faces look the way they look,” Whalen said.
There are biological selection pressures that may have shaped fearful expressions by allowing those individuals who were able to perform them to learn more about their environment and therefore survive in greater proportions.
Whalen also noted, however, “it’s not exclusive, [there are] multiple pressures shaping why faces look the way they look.”
For example, social pressures may also play a role. The article describes how fearful expressions increase the “babyishness” of the expresser, which is particularly important for infants needing attention or protection.
“When someone else makes a face, we mimic them to some degree,” Whalen said, explaining that this also contributes to the social factor.
Whalen said it remains unclear whether biological or social pressures are more significant evolutionarily in terms of developing different facial expressions.
“That’s the beauty of evolutionary theory,” he said. “It’s all kind of speculative, and we’re thinking about it after the fact.”
Further Reading:
Nature article