The next time a fight breaks out at an ice hockey game, blame the guy with the wide face. Although the findings aren't quite that clear-cut, new research indicates that males with larger facial width-to-height ratios tend to be more aggressive--both on and off the field.
When boys reach puberty, testosterone often lengthens and enlarges their jaws and makes their brow ridges more prominent. The hormone also increases their facial width-to-height ratio, a comparison of the distance between the cheekbones to the distance between the upper lip and brows. Last year, paleontologist Eleanor Weston of the Natural History Museum in London concluded from an analysis of skulls that this ratio is larger in males and that the difference is independent of the male-female inequality in body size. Intrigued by this finding, behavioral neuroscientist Cheryl McCormick and psychologist Justin Carré of Brock University in St. Catharines, Canada, decided to see if the ratio correlated with aggressiveness, which also depends on testosterone levels.
To find out, the researchers first measured facial width-to-height ratios in 88 male and female volunteers. They then gave the subjects a test that involved pushing buttons to gain points, to protect points from an opponent, or to take points away from the opponent. In the last instance, the player doesn't gain the point but merely gets the satisfaction of robbing the opponent. Males take points from opponents more often than do females, and psychologists regard the behavior as a reliable measure of aggressive tendencies. Results of the test didn't predict anything about faces for the women, but men with relatively wider faces tended to show more aggression; 15% of the individual differences in aggressive behavior could be explained by individual differences in facial ratios, the team reports online this week in the Proceedings of the Royal Society B.
Moving the experiments to the real world, the researchers plotted face ratios for college and professional ice hockey players from their photos on the Internet. They looked for a relationship between these measurements and an indicator of hockey aggression: time spent in the penalty box, a punishment for illegal behaviors such as throwing elbows or whacking opponents with a hockey stick. This time, the researchers found that 30% of the aggressive behavior exhibited by males could be predicted by their facial morphology.
The team concludes that this aspect of male facial structure may convey an "honest signal" of propensity for aggressive behavior. The authors point out that threatening expressions involve lowering the brow and raising the upper lip, which increases the facial ratio, suggesting that natural selection has made humans especially sensitive to it.
The study is "a really nice step forward in our understanding of the biology underlying social perception," says psychologist Ian Penton-Voak of the University of Bristol in the U.K. Weston has some qualms about the reliability of measurements taken from photos off the Web. Nonetheless, she says, "the implications of this are very exciting in terms of understanding how human behavior evolved" in relation to body design.