Researchers who believe in its predictive power say it reflects a fetus's exposure to testosterone and other hormones that guide development, including that of the brain. It tends to be lower in men-meaning their fourth fingers tend to be longer than their second-than in women.
That magic number is the ratio between the lengths of the second and fourth fingers, known as the 2D:4D ratio.
If papers published in the past 6 months are right, a single number is enough to show whether people are likely to suffer a premature heart attack, land first authorship on published papers, become dependent on alcohol, or put on fat around the middle.
