What 'Manly' Fingers Reveal

What 'Manly' Fingers Reveal | Digg Science:

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Hands are keys to the past, even if there isn't much past to tell. A glance at a boy's digit ratio — the relative length of index to ring finger —shows if he was exposed to high testosterone levels before birth. These testosterone levels even lead to "manlier" faces, even before the boy hits puberty, the research suggests.

In the uterus, before a baby is born, testosterone seems to have what the researchers call an "organizing effect" on the face — it helps controls how the face and other parts of the body (including the sex organs and yes, the fingers) develop. This means that researchers can use digit ratio as a measurement of testosterone exposure before birth, which comes from both the mother and the developing baby. A low ratio, where the index finger is shorter than the ring finger, indicates high testosterone levels, and the opposite for a high ratio.