Human faces can't express as many emotions as once thought, according to a new study from the Institute of Neuroscience and Psychology at the University of Glasgow.
Researchers found that there are only four basic emotions human beings can express, and not six like traditional science recognizes, the BBC reported. The findings were published earlier this week in Current Biology.
Humans were commonly thought to have six primary emotions: happiness, anger, sadness, fear, disgust and surprise.
However, by asking volunteers to evaluate three-dimensional models of faces, researchers found that facial expressions for anger and disgust were both characterized by a wrinkled nose. The expressions for surprise and fear were also both characterized by wide eyes, the BBC reported.
But as time went on, the volunteers were able to pinpoint a distinction between anger and disgust, as well as surprise and fear. This was contributed to evolution- the distinctions between expressions of anger and disgust, and surprise and fear developed because of our social needs, The Atlantic reported.
"These results show that dynamic facial expression models transmit an evolving hierarchy of signals over time," the study says, according to The Atlantic, "characterized by simpler, biologically rooted signals early in the signaling dynamics followed by more complex socially specific signals that finely discriminate the six facial expressions of emotion,"
Expressions for happiness and sadness remained different throughout the study. This leaves humans with four basic emotions: happiness, sadness, anger/disgust and surprise/fear.
Volunteers studied the facial expressions from 3D computer models based on photographs of real people. The volunteers were asked to identify the facial expressions based on the six traditional emotions, but were often confused at first about which face was angry or disgusted, and which were surprised or scared, the BBC reported.
Researchers want to conduct further studies to see if facial expressions vary by culture.
"Over time, and as humans migrated across the globe, socioecological diversity probably further specialized once-common facial expressions, altering the number, variety and form of signals across cultures," said head researcher Dr. Rachael Jack, the BBC reported.
