Correction: This article was edited to correct an error in the first paragraph regarding the mismatch between the ring and index fingers.

Men: Hold up your right hand. Are your index and ring fingers mismatched? Congratulations, you're more likely than men with matching digits to have a long penis.

A smaller ratio between the second and fourth fingers is linked to a longer stretched penis size, researchers report today (July 4) in the Asian Journal of Andrology. The findings go beyond providing a new finger ratio-based pick-up line for men in bars, however; researchers say that a quick look at a man's fingers could reveal his exposure to male hormones in the womb, providing a hint about his risk for hormone-driven diseases like prostate cancer.

The idea that men's finger ratio and hormone exposure are linked is not a new one. Studies have found that the ratio between the second and fourth finger is related to sperm count, likelihood of heart attack, hand preference, facial masculinity and more. One small 2002 study published in the journal Urology found a correlation between the length of the index finger and genital size in healthy men under 40, suggesting that testosterone exposure in the womb affects the growth of both.

Stretched penis length

In the new study, researchers at Gachon University Gil Hospital in South Korea recruited 144 volunteers 20 years of age and older who were going to undergo urological surgery. While the men were under anesthesia, the researchers measured their finger lengths and both their flaccid and stretched penis lengths. Stretched penis length is statistically correlated to the size of the penis when fully erect. [5 Myths About the Male Body]

The average flaccid penis length, the researchers found, was 3.0 inches (7.7 centimeters), with a range of 1.6 to 4.7 in. (4 to 12 cm). Stretched lengths ranged from nearly 3.0 to 6.7 in. (7.5 to 17 cm), with an average of 4.6 in. (11.7 cm).

The average ratio between the two fingers was 0.97, with a range of 0.88 to 1.12, making the differences hard to make out with the unaided eye. But the lower the digit ratio, the study found, the longer the penis was likely to be.

Testosterone in the womb

The prenatal hormone exposures and genetic processes that link fingers to penises are still unknown, the researchers wrote, though testosterone in the womb seems to play a role. If the findings hold, wrote Skidmore College biologist Denise Brooks McQuade in an editorial accompanying the study, digit ratio could provide an at-a-glance measure for doctors to gauge how much testosterone their patients were exposed to in the womb.

That makes digit-ratio measurement far more than a fancy bar trick, wrote McQuade, who was not involved in the research.

"'Hotness' aside, the value of digit ratio research for the biomedical scientist or clinician may come from the predictive abilities and risk-assessment qualities of the measurement for clinical conditions," she wrote.

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