Dogs snarl to reveal their teeth, lions roar menacingly, and frogs puff up to twice their normal size. And humans? We pull the “angry face”.
Rather than being the universal way of telling others that we feel cross, scientists now believe that the facial expression for anger evolved to make us appear more physically intimidating.
Even when we see aspects of an angry expression, such as flared nostrils, out of context we tend to rate the person displaying these characteristics as physically stronger.
Aaron Sell, who led the work at the University of California Santa Barbara, said: “In many animal species, before aggression, animals will pose in ways that enhance the cues of fighting ability that they have. Hair can stand on edge to make the mammal seem larger; lips are pulled back to make fangs look as large as possible.” In humans the lowered brow, jutting jaw and flared nostrils are all designed to convey physical might, he said.
Dr Sell and colleagues believe that we may initially have evolved the expression as a strategy to avoid conflicts with others. “The reason natural selection designed [the anger face] is that the individuals who made that face out-reproduced the other ones,” he said. “And they out-reproduced them because the people who made that face won their conflicts. The other people backed down because they looked at them and thought, ‘Wow, he looks really tough.’”
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Classic psychology experiments in the 1970s revealed that certain expressions of emotion, including happiness, anger, fear and disgust, are universal across cultures.
In the new study, published in the journal Evolution and Human Behavior, scientists tested the impact of the individual features of the angry face on a person’s appearance. The seven characteristics of anger were defined as flared nostrils, thinned lips, chin pushed up and out, the brow and brow ridge both lowered and the cheekbones and mouth both raised.
Starting from a computer-simulated image of a 20-year-old man, the scientists created pairs of faces for each of the seven features — one neutral, one with an anger-related change — and asked volunteers to assess each one for physical strength. Consistently, the faces with the added anger feature were rated as belonging to stronger men.
“Since people who are judged to be stronger tend to get their way more often, other things being equal, we concluded that the explanation for evolution of the form of the human anger face is surprisingly simple — it is a threat display,” said Dr Sell.
A previous study, published in 2005, proposed that the anger face evolved to make people look more threatening by making them look older, rather than stronger. However, this theory appeared to be ruled out by a second experiment by Dr Sell’s team, in which they showed that people did not rate the computer-generated images as any older on average than the neutral photos.
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