Place your right hand on the table with your fingers together. Which is longer, your index finger or your ring finger?
Unlikely as it may seem, medical research suggests that the answer - termed the "2D:4D digit ratio" -- might point to certain health and personality traits, including a higher risk of heart disease and breast cancer.
In women, the index finger (the second digit, or "2D") is usually about the same length as the ring finger (the fourth digit, or "4D"). In men, the ring finger is usually longer than the index finger. There's a lot of overlap, however, and men and women sometimes do have the opposite sex's ratio.
Scientists think that ratio -- the length of 2D to 4D - is programmed before birth, when the fetus is exposed to male sex hormones, or "androgens," in the uterus. It remains constant throughout life.
Everyone starts out female, which is humanity's "default" sex. Fetuses that get exposed to enough androgen during a critical stage in development become male. The rest stay female.
Studies have shown that the 2D:4D ratio may be a window on the womb, a marker for each individual's exposure to androgens before birth. Higher levels of androgens somehow favor growth of the ring finger, especially in the right hand. They make the ring finger grow longer than the index finger, and have a more masculinizing effect on the fetus.
Men usually have a low digit ratio. With the index finger 96 per cent of the length of the ring finger, their ratio is 0.96. With index and ring fingers roughly equal in length, most women have a "high" ratio of 1.0.
Studies showed that men with a low ratio (a ring finger longer than their index finger) are more fertile, aggressive and assertive, and have greater musical and sports ability. Men with a high ratio -- 2D and 4 D about equal length - have a higher risk of early heart disease.
Women with a high ratio (2D and 4D about equal in length) are more fertile and have a higher risk of breast cancer). Those with a longer ring finger were more aggressive and assertive and had a greater proclivity toward bisexuality and homosexuality.
The digit ratio has gotten little public attention. Much of that related to sexual orientation, thanks to a widely publicized 2002 study. With all the factors influencing sexual orientation, the idea of it being set before birth may be a double-digit over-simplification.
Men with a longer ring finger also get high marks on the sexual attractiveness scale from women. One scientist noted that women sometimes remark about being attracted to a man's "masculine-looking hands." Maybe, he speculated, they are unconsciously doing the math on that digit ratio.
For other disease/behavior digital links, check a 2002 book ("Digit Ratio: A Pointer to Fertility, Behavior and Health") written by one of the pioneers in this research, British scientist Dr. John T. Manning.