Scientists have identified the functional advantages that
caused the specific appearance of the anger face to evolve.
Scientists at University of California, Santa Barbara and
at Griffith University in Australia
say, "The expression is
cross-culturally universal, and even congenitally blind kids make this same
face without ever having seen one."
The anger expression employs seven different muscle groups
that contract in a highly stereotyped manner. The scientists sought to
understand why evolution chose those muscle contractions to signal the emotional
state of anger.
"Our earlier research found that anger evolved to motivate effective
bargaining behaviour during conflicts of interest," noted Aaron Sell, a
lecturer at the School of Criminology at Griffith University
Starting from the theory that anger is a bargaining emotion, the scientists
reasoned that the first step is communicating to the other party that the
anger-triggering event is not acceptable, and the conflict will not end until
an implicit agreement is reached.
This is why the emotion of anger has a facial expression associated with it.
"But the anger face not only signals the onset of a conflict. Any
distinctive facial display could do that.
We hypothesised that the anger face evolved its specific
form as 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," said Sell.
Using computer-generated faces, the scientists then demonstrated that each of
the individual components of the anger face made those computer-generated
people appear physically stronger.
For example, the most common feature of the anger face is
the lowered brow. Researchers took a computerised image of an average human
face and then digitally morphed it in two ways: One photo showed a lowered
brow, and the other a raised brow.
"With just this one difference, neither face appeared 'angry'. But when
these two faces were shown to subjects, they reported the lowered brow face as
looking like it belonged to a physically stronger man," said Sell.
The experiment was repeated one-by-one with each of the other major components
of the classic anger face - raised cheekbones (as in a snarl), lips thinned and
pushed out, the mouth raised (as in defiance), the nose flared and the chin
pushed out and up.
As predicted, the presence by itself of any one of these muscle contractions
led observers to judge that the person making the face was physically stronger.