Scientists have traditionally held that people have six basic emotions: happy, sad, angry, surprised, afraid, and disgusted. But a new study reduces that number to just four by combining "angry" with "disgusted" and "surprised" with "afraid." Those pairings share the same biological roots, the Glasgow researchers suggest. Their conclusion is based on subjects' responses to computer animations of facial expressions, the Atlantic reports. Participants were supposed to divide the animations into the six classic emotional categories.
But the subjects saw "angry" and "disgusted" as the same when the emotion first appeared on a face; both included, for example, a wrinkled nose. Both "surprised" and "afraid," meanwhile, featured raised eyebrows. The distinctions didn't become apparent to observers until some time had gone by. To the researchers, that indicated that the differences between the emotions were more social than biological, leaving four basic emotions: happy, sad, angry/disgusted, and afraid/surprised. "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," the study's head says, per the BBC. (Read more emotion stories.)