As a result, most men have ring fingers that are longer than their index fingers, and the reverse is true in women.

Differences in finger length have been repeatedly linked to a range of human traits, from aggression to musical ability to sexual orientation. There are also connections to health problems such as autism, depression, heart attacks, and cancer.

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"It's difficult to look at an adult or a newborn child and determine what was happening during their embryonic development," said study leader Zhengui Zheng, a developmental biologist at the Howard Hughes Medical Institute in Florida.

"But the discovery that digit proportions reflect the prenatal hormonal environment helps us to explain all those correlational studies," said