London: The length of a man's fourth (ring) finger has been linked to his libido. The more testosterone a foetus is exposed to, the longer the ring finger is supposed to be.
Which explains why men's fourth fingers are usually longer than their index (next to the thumb) fingers, while the reverse is true in women.
Now scientists have figured out that the fourth finger's size depends on levels of the male and female sex hormones in the foetus, the journal Proceedings of the National Academy of Sciences reports.
Ring finger length has been linked with sperm count, aggression and sports prowess, while high testosterone levels are tied with a higher sex drive, according to the Daily Mail.
Martin Cohn and Zhengui Zheng, biologists at the University of Florida, say the fourth finger is packed with receptors for sex hormones.
They took groups of pregnant mice - a species with a similar finger-length ratio to humans - and controlled the genes which affect their oestrogen and testosterone levels.
Increased testosterone affected the size of the ring finger in the hind paws of the baby mice, which are like the human left hand in being receptive to sex hormones.
Cohn said: "Sex hormones affect finger length, and the ratio is fixed before the bone has even developed."
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