Have you ever taken a good look at yourself in the mirror when you’ve been really fired up? We don’t have to explain to you what anger looks like, and we certainly don’t have to explain how seeing it on someone else makes you want to run far, far away. At a very rapid pace.We now know that the reason we can all picture this quintessential (and scary) face so vividly is because it’s part of our basic biology—thanks to research at UC Santa Barbara and Griffith University in Australia. We humans have evolved so that seven specific muscles contract in a specific way to signal anger. And the coolest part is we all do it, no matter our age, sex, or the culture we grew up in.

“The expression is cross-culturally universal, and even congenitally blind children make this same face without ever having seen one,” notes lead author Aaron Sell, a lecturer at the School of Criminology at Griffith University in Australia. Just like our eye color or whether we’re right- or left-handed, it’s wired deep within us.

The study, published in the journal Evolution and Human Behavior, answers why evolution chose these particular muscles to contract when we’re PO’d. And it all comes down to anger’s raw function: to give the angered an upper hand in bargaining during a conflict. The result of the muscle contractions is the face that every human associates with anger, and makes you appear more powerful in a conflict.

Starting with their assumption that displaying anger boosts your bargaining power, the researchers explain why anger has such a distinct facial expression associated with it: The anger face communicates to the second party that whatever caused the anger is not acceptable. And that face ain’t going anywhere until an agreement is reached.

But there’s more. “We hypothesized that the anger face evolved its specific form because it delivers something more for the expresser,” says Sell. “Each element is designed to help intimidate others by making the angry individual appear more capable of delivering harm if not appeased.”

Using computer-generated images, researchers demonstrated that each component of the anger face makes a person appear physically stronger—ergo, more capable of inflicting harm if things don’t go his way. For example, by altering just an eyebrow to be either lowered or raised, the percevied strength of the individual changed. “With just this one difference, neither face appeared ‘angry,’ ” says Sell. “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.

“Other key facial features that make up the anger face include raised cheekbones, thinned and pushed out lips, mouth raised in defiance, nose flared, and chin pushed out and up. Just as with the eyebrows, each time one of these facial features was manipulated, viewers assumed the person was physically stronger.”

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,” says Sell. Which is that you refuse to accept the situation, and you’re ready to fight until you get your way—so be afraid, be very afraid.