Why are some men so much more aggressive than others?

A partial answer may come from a study in Biological Psychology, showing that the ratio of a man's second finger to his fourth finger appears to predict aggression. The amount of testosterone a baby is exposed to in his mother’s uterus determines how long his fourth finger grows. So men who have been exposed to high levels of testosterone in utero have a larger ratio of the fourth (“ring”) finger to the second (“index”) finger and therefore are more prone to physical aggression later in life.

The author of this study states: “This study shows that events in the womb have subtle effects on children's personality." Previous studies have shown that men with higher ratios of the fourth to second finger may be better in sports and are usually more dominant and masculine. On the other hand, these men are at higher risk for autism and immune deficiency. Men have larger finger ratios than women. The authors cautioned that these findings link a larger finger ratio to "a tendency toward physical aggression". They do not show that all men with larger ratios are more aggressive.

Biological Psychology, March 2005

August 7, 2005

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