WOMEN can discover just how sexually driven their date is just by looking at his hands.
Because scientists have discovered that the length of a man’s fourth finger is linked to his libido.
Researchers discovered 'ring finger' size is determined by levels of the male and female sex hormones even before a baby is born.
The more testosterone – the male sex hormone – a baby is exposed to, the longer his ring finger is likely to be.
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.
Dr Martin Cohn and Dr Zhengui Zheng, biologists at Florida University, 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 gave the baby mice a bigger right paw, but made little difference to the left. This, the scientists say, is because the right paw – like the human left hand – is more receptive to sex hormones.
By comparison, mice exposed to higher levels of oestrogen had a shorter right paw and a markedly more ‘feminised’ appearance. 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.
Dr Cohn said: ‘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.’