When we get angry, we all tend to make the same face -- lowering our eyebrows, clenching our jaws, and flaring our nostrils. But as to why people all around the world make that same angry face, scientists really weren't quite sure.
A new study suggests that our facial expression of anger evolved because it made us appear physically stronger.
"Each element is designed to help intimidate others by making the angry individual appear more capable of delivering harm if not appeased," study co-author Dr. Aaron Sell, an anger researcher and lecturer at Griffith University in Australia, said in a written statement. “The expression is cross-culturally universal, and even congenitally blind children make this same face without ever having seen one."
For the study, the researchers showed 141 men and women different computer images of a male face. Some of the images were not manipulated in any way, but others were morphed so that the face included one of the key facial features associated with anger.
For instance, some of the photos were manipulated to include cheekbones positioned in the shape of a snarl, or lips pushed out as if pursed, or a raised chin. Each manipulated photo was shown next to the original untouched version, and the viewers were asked to judge which face made the man in the image appear physically stronger.
None of the faces appeared "angry" -- even those that were manipulated, Sell said in the statement. But what did the researchers find?
Most of the men and women in the study indicated that the image that included one of the features of an "angry" face indeed made the man making the face appear stronger.
"Just like a frog will puff itself up or a baboon will display its canines," study co-author Dr. Leda Cosmides, a psychology professor at the University of California, Santa Barbara, said in the statement.
"What is most pleasing about these results is that no feature of the anger face appears to be arbitrary; they all deliver the same message," study co-author Dr. John Tooby, a professor of anthropology at the University of California, Santa Barbara, said in the statement. "The face immediately organizes itself to advertise to the other party the costs of not making the situation more acceptable."
The study was published in the September 2014 edition of the journal Evolution and Human Behavior.