The length of a man’s index finger relative to his ring finger can predict his likelihood of physical aggression.

It’s long been known that the length of the index finger relative to the ring finger differs between men and women.

Researchers have also recently found a direct correlation between finger length and the amount of testosterone a fetus is exposed to in the womb—the shorter the index finger relative to the ring finger, the higher the testosterone exposure.

And, show Hurd and Bailey, the higher the likelihood of physical aggression.

“More than anything, I think the findings reinforce and underline that a large part of our personalities and our traits are determined while we’re still in the womb,” says Peter Hurd of the University of Alberta in Canada.

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