Male aggression related to index finger length

Previous studies have discovered that finger length in men is directly correlated to the amount of male sex hormone testosterone they were exposed to in the womb. A new study just released from University of Alberta reveals that men with longer ring fingers compared to their index fingers tend to be more physically aggressive.

Researchers say it has long been recognized that the length of the index finger relative to the ring finger differs between men and women. In women, the difference in the length of their ring finger relative to their index finger is small. Meanwhile, men tend to have a bigger length difference between the two fingers.

A number of scientists have performed research in this area and have tied some aspect of behavior and central nervous system development to the amount of testosterone baby boys are exposed to in the uterus, which also influences finger length.

Canadian professor of psychology Dr. Peter Hurd and his graduate assistant Allison Bailey measured the fingers of 300 male and female undergraduates at the University of Alberta. The results of their study will appear in the March issue of Biological Psychology.

Their results showed that men had smaller finger length ratios than women. In addition, the shorter the index finger was relative to the ring finger, the more likely the male students scored higher on scales of physical aggression. However, they found no correlation between finger lengths and people who are prone to exhibit verbally aggressive, angry, or hostile behaviors.

The study's findings did not apply to women. Generally speaking, women's index and ring fingers are almost equal in length, because they're exposed to less testosterone in the womb.

However, Hurd says finger lengths only, "explain about five percent of the variation in these personality measures, so research like this won't allow you to draw conclusions about specific people."

In a press release, Hurd added, "For example, you wouldn't want to screen people for certain jobs based on their finger lengths, but finger length can tell you a little bit about where personality comes from, and that's what we are continuing to explore."

Although researchers say finger length only accounts for a small portion of the differences in men's aggressive behaviors, they explain that the results are consistent with previous studies that have linked men's finger length to the amount of testosterone a fetus is exposed to in the womb.

"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 in a news release. Hurd also noted that both testosterone exposure and finger length may be influenced by a "deeper third variable."

Evolutionary biologist John Manning, at the University of Liverpool, has noted that heavier testosterone exposure may also affect development of the right side of the brain, which controls both visual and spatial judgment. Therefore, some researchers propose that ring-finger length may predict athletic prowess as opposed to aggression.

Manning observed that relatively longer fingers, especially in the ring finger, may indicate increased risk for depression in men, but not in women.

Hurd, on the other hand, plans to publish research suggesting that men having more feminine finger-length ratios are more prone to depression. Previous research has shown that men with smaller differences in the length of their ring and index fingers are at higher risk of autism and immune deficiency.

Hurd is conducting ongoing research in this area. He next plans to investigate whether there is any correlation between finger length and male hockey players' penalty records for contact and fouling during matches.