Are you a guy? Hold out your hand with your fingers out. Is your index finger shorter than your ring finger? Is it much shorter? You’re a dangerous guy. Get help.
It seems, according to a recent study, that that finger length in men is determined by the amount of testosterone the fetus is exposed to in the womb. A shorter index finger relative to the ring finger means more testosterone, which means that the guy is more likely to be physically aggressive later on in life. The correlation doesn’t work for women: not enough testosterone.
Its a general correlation across populations (not for individuals), and it seems to apply only to physical aggressiveness, not to being verbally aggressive, angry, or hostile. (I was joking in that first para). Still: weird!
(I got it from science blog)