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Lop-sided features linked to temper

August 24, 2004 By Michael Hopkin This article courtesy of Nature News.

Poor development in the womb could lead to aggressive behaviour.

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Sometimes it can be worth judging by appearances: it seems that people with less symmetrical features are likely to be more aggressive. In a study of stressful telephone conversations, those with uneven faces and bodies were more prone to angry reactions.

A lack of symmetry is known to be a hallmark of slightly imperfect development, so the researchers speculate that people with ill-matched external features may also have small defects in their nervous systems, which impair their ability to control aggressive impulses.

A link between asymmetry and aggression has been suggested before but never properly tested. Previous attempts have relied on subjects to report faithfully their own levels of aggression, or used violent offenders who are often abnormally aggressive.

Zeynep Benderlioglu of Ohio State University in Columbus and her colleagues got around the problem by recruiting 100 volunteers and tricking them. After measuring their ears, wrists, palms, ankles, feet and elbows to quantify their symmetry, the researchers told the subjects that they were testing the influence of symmetry on persuasive skills.

On the line

The researchers asked each of the volunteers to make two telephone calls attempting to solicit charity donations, promising them free cinema tickets if they were successful. What they did not reveal was that the charity was fake, and the prospective charity donors were really members of the team primed to react in a certain way.

The first 'charity target' was friendly, claiming they had no money to give and apologizing profusely. But the second was far more hostile, being rude to the volunteers and claiming that the charity was a waste of money.

What the volunteers also did not know was that the researchers had rigged the telephones to measure how forcefully they replaced the receiver after the call. "I do feel quite guilty for deceiving them," says Benderlioglu. "But it was in the name of science."

Rude rage

Asymmetrical subjects were more likely to slam the telephone receiver down at the end of a call than symmetrical people, indicating that rejection made them angrier, the researchers report in the American Journal of Human Biology1.

Asymmetry is generally caused by conditions in the womb that are less than ideal, points out Benderlioglu. She believes the result shows that the environment in which a fetus develops has subtle effects on the nervous system as well as the more obvious effects on external features. Mothers who drink, smoke or are ill during pregnancy may be more likely to end up with unruly children, she suggests.

Battle of the sexes

The team also found differences between the responses of men and women. Female volunteers were more likely to be enraged by the rude call recipients. But male subjects slammed the phone down harder on the polite charity targets.

So why did the men not become the most angry when faced with both rejection and rudeness? Men can become aggressive more quickly then women, but are also quicker to back down if things start to look hairy, Benderlioglu suggests. "They don't seem to be able to tolerate as much anger as women," she says. "Men are much more attentive to their bodily state, such as heart-beat."

Nevertheless, both sexes, no matter how symmetrical, can suffer unproductive attacks of rage. As a final part of the study, the researchers asked volunteers to select one of three follow-up letters to send to the charity targets. Subjects generally chose the harshest letter for the rude respondent, telling them that they were doing "a disservice to the community", which was hardly the best way to encourage future donations.

References

  1. Benderlioglu Z., Sciulli P. W. & Nelson R. J. Am. J. Hum. Biol., 16. 458 - 469 (2004).

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