Finger Ratios, Prenatal Testosterone, and Behavior
Research done at the University of Alberta found a connection between the length of the male index finger relative to the ring finger and the tendency to be aggressive. No such connection was found in women.
Scientists have known for more than a century that the finger-length ratio differs between men and women.
In women, the two fingers are usually almost equal in length, as measured from the crease nearest the palm to the fingertip. In men, the ring finger tends to be much longer than the index.
Recently, scientists found a connection between finger lengths and the amount of testosterone that a fetus was exposed to in the womb: the shorter the index finger relative to the ring finger, the higher the amount of prenatal testosterone. The new study found such a fetus is more likely to be a physically aggressive adult, according to Peter Hurd and his graduate student Allison Bailey. The connection was found only with physically aggressive behavior, not with verbal aggression or other forms of hostility.
Other studies looking at finger length ratio have suggested that, in men, a long ring finger and symmetrical hands are an indication of fertility, and that women are more likely to be fertile if they have a longer index finger.
One study found boys with shorter ring fingers tended to be at greatest risk of a heart attack in early adulthood, which was linked to testosterone levels.
Another recent study had found women exposed to higher levels of testosterone in the womb, and hence a more ‘male’ pattern of finger length, displayed more frustrated behaviour when answering challenging telephone calls than other women.
A 2003 report in Chemical & Engineering News, a weekly newsmagazine published by the American Chemical Society, said “flawed brain chemistry, brain damage, genetic defects, an unhealthy psychological environment” all contribute to violent behavior.
Another study by Hurd, to be published in the journal Personality and Individual Differences, find that men with more feminine finger ratios are more prone to depression.
Finger lengths explain only about 5 percent of the variation in these personality measures.