ASYMMETRY OF BODY PARTS LINKED TO AGGRESSIVE TENDENCIES

How aggressive will a person become if provoked? One possible clue, researchers at Ohio State University say, is how asymmetrical the person's body parts are.

Zeynep Benderlioglu and colleagues note that asymmetries, such as differently sized ears or feet, can reflect stressors during pregnancy, such as poor health or exposure of the fetus to tobacco, alcohol, or other toxins. "The same stressors, Benderlioglu says, "will also affect development of the central nervous system, which involves impulse control and aggression."

To determine if asymmetries were associated with levels of aggression, Benderlioglu and colleagues recruited 51 male and 49 female college students to participate in a laboratory study in which the subjects made phone calls asking for charitable donations. While the participants believed that the calls were real and that the researchers were studying the persuasiveness of their sales pitches, in reality the callers reached research assistants involved in the study. One respondent reacted politely but declined to donate, while the second was rude and confrontational. To judge how aggressive the callers became, the researchers measured the forcefulness with which they slammed the phone receivers down after their appeals were rejected.

Before starting the experiment, Benderlioglu and colleagues measured the symmetry of the participants' fingers, palm heights, wrist diameters, elbow widths, ear sizes, foot breadths, and ankle circumferences. They found that, in general, the more asymmetry a subject exhibited, the more aggressive he or she would be in hanging up the phone. Interestingly, a greater degree of asymmetry in male subjects was associated with increased aggression only during the low-provocation calls, while increased asymmetry in women was associated with aggression only during the high- provocation calls. The same pattern also occurred when the researchers measured testosterone levels, with high testosterone predicting male aggression in the low- provocation call and female aggression in the high- provocation call.

The researchers say their findings suggest that individuals with both high levels of body asymmetry and high levels of testosterone may be particularly aggressive when provoked.

"Fluctuating asymmetry predicts human reactive aggression," Z. Benderlioglu, P. W. Sciulli, and R. J. Nelson, American Journal of Human Biology, Vol. 16, No. 4, July-August 2004, 458-69. Address: Zeynep Benderlioglu, Department of Psychology, Ohio State University, Columbus, OH 43210, benderlioglu.1@osu.edu.

"Aggressive tendencies may be revealed by asymmetry in body parts, study finds," news release, Ohio State University, August 20, 2004.