The evolutionary mystery of why our faces contort when we are scared has been solved by a team of Canadian neuroscientists.
When our facial expression shifts to one of eye-bulging, nostril-flaring fear, our ability to sense attackers or other imminent danger improves dramatically, researchers found.
The findings lend support to an idea first laid out by Charles Darwin in one of his less well-known tomes, The Expression of the Emotions in Man and Animals, published in 1872. Darwin noted that facial expressions of emotion were often remarkably similar across human cultures, and even the animal kingdom, implying they may have a common evolutionary benefit.
"Most people think expressions are social signals, that they are intended to communicate what someone's feeling. We're saying they probably evolved as a sensory function first, even if they do help convey our feelings to others," said Adam Anderson, a cognitive neuroscientist who led the study at the University of Toronto.
I didn't find this very convincing. In this study, participants were told to mimic computer modeled facial expressions of fear by furrowing their brows, widening their eyes and flaring their nostrils. The researchers found that the mimicry resulted in "a subjectively larger visual field, faster eye movements," increased air volume and increased velocity of airflow during inspiration. When students mimicked expressions of disgust, the researcher found opposite effects. Their take on the findings was that facial expressions alter perception to prepare us for action and that facial expressions probably evolved as individual protective mechanisms first and communicative systems only secondarily.
This seems plausible, but I think the authors are overreaching in their conclusion. First, the participants only mimicked facial expressions. It isn't clear that any effects on perception would be the same if the expressions arose spontaneously along with genuine emotional reactions. Second, I don't believe the researchers have come close to establishing that these small effects on outward indicators of perception actually confer a survival advantage.