In men the index finger is usually shorter than the ring finger, but in most women it's the other way around, although in some women the fingers are of equal length. In mice the digit ratio corresponds to the female-male hormonal balance in the womb during the week digits form; androgen apparently produces a longer ring finger.

Researchers study these ratios to see if they can serve as markers for certain human attributes. So far in 2012, studies have found that girls with a masculine ratio do not get lost as easily; that a feminine ratio in heterosexual girls is associated with bulimia; and that boys with more masculine ratios have more typically masculine facial features.