In the film The Good, the Bad and the Ugly, the bandit Tuco traipsed over half the West to be crossed and double-crossed before learning how to distinguish between the "two kinds of people ... in this world."
Now researchers in a Canadian lab have discovered just how easy that judgment can be, and what's more, they say that we can spot the difference in the flash of an eye.
A study published in October's Psychological Science found that people use a facial trait called the width-to-height ratio to instantly gauge the aggressive potential of others.
The team from Ontario's Brock University included Department of Psychology Centre for Neuroscience researchers Cheryl McCormick, Justin M. Carré and Catherine J. Mondloch. McCormick, who led the effort, said the project came on the heels of a 2007 study in the United Kingdom that showed that not only do males develop facial traits during puberty differentiating their features from those of females, male facial proportions also begin at that time to diverge.
Prior to the U.K. study, McCormick said most differences in facial proportions had been thought to correlate most reliably with an individual's stature. But in the case of the width-to-height ratio, she said the difference was not correlated with body size, which "signaled that it might have some other meaning or some other purpose."
In a widely reported 2008 study published in the Proceedings of the Royal Society: Biological Sciences, McCormick and her colleagues measured the width-to-height ratio from pictures of individual men and tested their aggressive tendencies in the laboratory. The results showed a high correlation between the size of this ratio and how aggressively they behaved in a game of provocation.
"We found it intriguing that a measure of the face was associated with behavior," she said. Turning to real world experience, McCormick said, "In that same paper, we reported that when we looked at this measurement of the faces of hockey players in the NHL, it was correlated with penalty minutes."
In the new study, participants were shown photos of men, controlled for ethnicity and other cultural cues such as facial hair, and were asked to rate the individuals on a variety of characteristics, including how aggressive they thought the person would be if provoked. McCormick said the results were startling; respondents could not only accurately gauge the aggressive tendencies in the men, they could do so "in as little as 39 milliseconds."
Participants' estimates were "even more strongly correlated with the facial width-to-height ratio" than with how the men actually performed on the aggression test.
McCormick said the responses were automatic and accurate even among participants reluctant to make a judgment based on an image they barely had time to examine.
"That was strong evidence suggesting that the facial width-to-height ratio is some kind of metric that is conveying information about that individual to other individuals," she said.
"We already know that people make snap judgments about people all the time," McCormick said. "In most studies in psychology, it's been very hard to find a lot of accuracy in these snap judgments. It's unusual to be able to say there is something in the face that actually is alerting us to how aggressive someone can be," and "it's more surprising that these judgments have some accuracy to them."
However, one might want to take a breath and count to 10 before adopting the stance Clint Eastwood's character dishes to taunt his foe in the classic western.
In fact, co-author Mondloch said the results of these studies "raise more questions than they answer," and current research asks how people acquire the skill to make these instant judgments, and whether the phenomenon might be influenced by culture.
Although McCormick is comfortable speculating that the facial attributes observed among aggressive males might be linked to a surge in testosterone levels during adolescence, she cautioned, "Yes, you may have some accuracy with your snap judgments, but, they're far from perfect; so you should always collect more data about an individual's behavior than simply that first snap judgment."
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