Monday, 25 August 2014
A popular view has it that, besides reliably conveying anger, this particular constellation of facial movements is arbitrary and serves no other function. A team of evolutionary psychologists led by Aaron Sell disagrees. They think the anger face also makes the angry person look stronger. This fits their "recalibration theory of anger" that sees the emotion as an aggressive threat. An angry animal or person is communicating the costs that they will inflict on others if they do not get what they want. By making an angry person look stronger, so the theory goes, the facial expression gives weight to the threat of aggression, likely influencing the target's judgment about the seriousness of the threat.
To test this, Sell and his colleagues created pairs of faces using a computer programme. They began with a 20-year-old male face, morphed from averages of many faces, and then calibrated it so that for each of the seven distinguishing features of anger (lowered brow, raised lips, raised mouth, widened nose, enlarged chin, lips thinned, lips pushed forward), they created a pair of contrasting faces. One face in each pair displayed one angry feature, the other face showed the opposite feature. For example, one face showed lowered brows, the other face in the pair showed raised brows. In this way, the seven distinguishing features of anger were isolated.
Thirty-five student participants then looked at the facial pairs and indicated in each case which face they thought looked stronger. The key finding? Each anger-related facial feature when displayed on its own attracted higher ratings of perceived strength. This implies each element of the anger expression contributes to making a person appear stronger.
Further experiments ruled out an alternative explanation - perhaps angry faces actually serve to make a person look older, and this leads to ratings of greater strength because observers assume a slightly older man is stronger than a 20-year-old. One way the researchers tested this was to show participants pairs of morphed faces of a 60-year-old man, in which case looking older presumably wouldn't be associated with greater strength. Three of the angry facial features actually led him to being rated as younger, with only two prompting ratings of being older. Moreover, participants rated the man as stronger when he displayed six of the seven angry facial features.
"The current study is the first systematic test of the individual components of the anger expression," the researchers said. "And in so doing it confirms that these features are improbably well-designed to solve the adaptive problem of bargaining with threats of force." The results are also consistent with a range of other research, including the finding that several features of an angry expression tend to be more prominent in men than women (this fits with the idea that aggression is a more important bargaining tool for men); that stronger and bigger men get angry more easily; and that men's fighting ability can be discerned from the shape of their face. Looking at the study's limitations, it's a shame the researchers didn't investigate women's expressions of anger, and that they relied on student participants.
Sell, A., Cosmides, L., & Tooby, J. (2014). The human anger face evolved to enhance cues of strength Evolution and Human Behavior, 35 (5), 425-429 DOI: 10.1016/j.evolhumbehav.2014.05.008
Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.