A University of Alberta study found that the length of a man's index finger relative to his ring finger predicts his predisposition to being physically aggressive.
Study co-author Dr. Peter Hurd admits he initially thought it was ridiculous to look for a link between finger length and aggression.
But the results of the study showed that the shorter the index finger relative to the ring finger, the greater the amount of prenatal testosterone, and the more likely the man will be physically aggressive.
The Alberta team found no link between finger length and aggression in women, and also no correlation between finger length and nonphysical forms of aggression, such as verbal aggression.
Researchers have long known that the index-to-ring-finger ratio differs considerably between men and women. In fact, in another study, Hurd found that men who had 'feminine" finger ratios tended to be more prone to depression.
Research has suggested that the length of men's fingers depends on exposure to testosterone in the womb.
Hurd says, "The findings reinforce...that a large part of our personalities and our traits are determined while we're still in the womb."
He stresses that "research like this won't allow you to draw conclusions about specific people." It can only tell you a little bit about where personality comes from, and that's what we are continuing to explore," he says.
Hurd is continuing his research on physical aggression by comparing hockey players' finger lengths to the number of penalty minutes they get in a given season.
The Stress-Aggression Link Scientists believe there may be a biological link between stress and aggression.
This could explain, for instance, why people turn violent when they are stressed—such as experiencing road rage after the stress of being stuck in traffic. It also may answer why it's so hard to calm down after getting mad the rage continues to fuel stress hormones.
Behavioral neuroscientists in the Netherlands and Hungary found that there is a direct connection between the part of the brain that controls aggression and the hormones that trigger stress at least in rats.
When rats are subjected to stress, the researchers say, the part of the brain that triggers aggression is activated. Conversely, when rats were induced to be aggressive, blood levels of a stress hormone increased.
The rodents were studied because their neurophysiology-brain hardwiring-is similar to that of humans.
"It is well known that these stress hormones, in part by mobilizing energy reserves, prepare the physiology of the body to fight or flee during stress. Now it appears that the very same hormones talk back to the brain in order to facilitate fighting." says study author Menno Kruk, from the Leiden/Amsterdam Center for Drug Research.
His findings may help researchers find ways to prevent pathological violence in humans.