Digit ratio: Finger length is related to physical aggression

According to a new study by researchers at the University of Alberta the length of a male's index finger relative to his ring finger can predict how physically aggressive a man is. Women do not show a similar effect.

This measure of finger length, also known as digit ratio, has been shown in previous research to also be related to sexual orientation, number of sexual partners and scientific ability.

Lead author psychologist Peter Hurd said it has been known for over a century that there is a difference in digit ratio between males and females. Recently, researchers have determined a direct correlation between digit ratio and testosterone levels in the womb during fetal development. A shorter index finger relative to the ring finger--a lower digit ratio--indicates a higher level of prenatal testosterone.

"More than anything, I think the findings reinforce and underline that a large part of our personalities and our traits are determined while we're still in the womb," said Hurd.

The research, published in the March issue of Biological Psychology, was based off surveys and hand measurements of 300 college students.

They found no relationship between digit ratio and tendency for verbally aggressive, angry or hostile behavior, but there was to physically aggressive behavior.

Hurd is conducting other studies on digit ratio, including relating it to hockey players' penalty minutes. A similar study by Hurd to be published later this year shows that males with a more feminine digit ratio are more likely to be depressed.

"Finger lengths explain about five per cent of the variation in these personality measures, so research like this won't allow you to draw conclusions about specific people. For example, you wouldn't want to screen people for certain jobs based on their finger lengths," Hurd said. "But finger length can you tell you a little bit about where personality comes from, and that's what we are continuing to explore."