A new study has revealed that the length of a man’s fourth finger is linked to his libido.
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“The more testosterone – the male sex hormone – a baby is exposed to, the longer his ring finger is likely to be,” they said.
Their study explains for the first time why men’s fourth fingers are usually longer than their index fingers, while for women it is the other way round.
Ring finger length has previously been linked to sperm count, aggressive behaviour, sexual orientation and sports prowess, while high levels of testosterone are associated with a higher sex drive.
Professor Martin Cohn and Dr Zhengui Zheng, biologists at the University of Florida, say the fourth finger is packed with receptors for sex hormones.
In the experiment, 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 the scientists say, are like the human left hand in being receptive to sex hormones.
The levels of testosterone in the womb determine the length of a ring finger, explaining why men’s fourth fingers are usually longer than women’s.
By comparison, mice exposed to higher levels of oestrogen, had a more ‘feminised’ appearance in having a shorter ring finger. Almost all the male mice in this group had genital defects.
The results could have implications for diseases linked to the hormone balance, such as prostate and breast cancer.
“Sex hormones affect finger length, and the ratio is fixed before the bone has even developed. This happens during a narrow window of development but it stays fixed throughout life,” Cohn added.