Angry facial expressions are a communication tool, essentially conveying the message that the incensed individual is not a happy bunny. But researchers at UC Santa Barbara in the US and Griffith University in Australia wondered why we've all evolved this characteristic angry expression.
To find out, they took a computer-generated image of a typical male face and digitally altered it to have either a raised or a lowered brow.
"With just this one difference, neither face appeared 'angry'," says Dr Aaron Sell at Griffith University. "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."
Similar experiments were carried out with other parts of the face, raising the cheekbones to simulate a snarl, thinning the lips, flaring the nostrils or pushing out the chin. The presence of any one of these 'angry' facial features led the participants to judge that the person was physically stronger.
So like a frog puffing itself up or a dog baring its teeth, our angry faces have evolved as a way of intimidating others and displaying strength.
"Since people who are judged to be stronger tend to get their way more often, other things being equal, the ... explanation for evolution of the form of the human anger face is surprisingly simple - it is a threat display," says Sell.
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