Researchers from the University of California, Santa Barbara and Griffith University in Australia are studying the universal "anger face," which appears to be a part of the basic biology of human beings.
The researchers have found what the caused the evolution of the angry face of human beings, and have published their report online at the Evolution and Human Behavior journal.
According to the study, the facial expression for anger is universal and crosses cultures, even to the point that even the angry faces of children that have been born blind exhibit the same features without ever seeing one.
The facial expression of anger uses the contractions of seven different groups of muscles in the human face. The researchers studied why the contractions of those specific groups of muscles are the ones chosen by evolution to create angry faces.
This study of the evolution of angry faces, however, is just a part of a bigger set of researches that study the evolutionary function of the emotion of anger.
"Our earlier research showed that anger evolved to motivate effective bargaining behavior during conflicts of interest," said Aaron Sell, the lead author of the study and currently a lecturer at the Griffith University's School of Criminology.
The co-authors of the study are UCSB psychology professor Leda Cosmides and UCSB anthropology professor John Tooby. Cosmides and Tooby are co-directors of UCSB's Center for Evolutionary Psychology, where Sell was a former postdoctoral scholar.
"We hypothesized that the anger face evolved its specific form because it delivers something more for the expresser: Each element is designed to help intimidate others by making the angry individual appear more capable of delivering harm if not appeased," Sell said.
Cosmides noted that our human ancestors believed that greater strength from the upper body means a greater ability to cause harm, leading to the hypothesis that an angry face would make an individual look stronger.
The researchers showed, through computer-generated faces, that every component that makes up an angry face makes the person look stronger. Examples of the components include a lower brow, raised cheekbones, thinned and pushed out lips, a raised mouth, a flared nose and a pushed out and up chin.
When shown to subjects, the faces that had these components were said to be belonging to a physically stronger human.
"In the final analysis, you can think of the anger face as a constellation of features, each of which makes you appear physically more formidable," said Sell.