Penis size, sex drive tied to men's finger length: Why?

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(CBS) Women often glance at men's ring fingers to tell if they're married. But in addition to marital status, scientists say a man's ring finger can reveal his sexual orientation, libido level, penis size, and even risk for certain diseases like prostate cancer.

Penis size linked to finger measurements, say Korean scientists

And now scientists say they know why.

A new study reported sex hormone exposure in the womb determines finger length, and this finding could offer insights into the origin of other behaviors and diseases.

For the study - published in this week's issue of Proceedings of the National Academy of Sciences - researchers studied digit length in mice, which are considered to have similar digit ratios as human males and females. When researchers exposed the mouse embryo to more male hormones, the mouse had a proportionally longer fourth digit. More estrogen resulted in a more female-looking mouse, and smaller fourth digit.

"When they added testosterone they got super male ratios, and when they added estrogen, super female ratios," Dr. John T. Manning, evolutionary psychologist at Swansea University in England, who was not involved in this study, said in a written statement. "And they've provided us with a list of 19 genes that are sensitive to prenatal testosterone and prenatal estrogen."

Some of the 19 genes may help scientists discover the origin of certain behaviors and diseases, and may help doctors find new treatments for diseases like ALS and prostate cancer, which have been linked to finger length.

Said Manning, "We can now be more focused in our examination of the links between digit ratio and sex-dependent behaviors, diseases of the immune system, cardiovascular disorders and a number of cancers."

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