The link between a man's ring finger and sex!

The longer his finger, the higher his libido!

Here's advice for ladies who are really passionate about someone -- check his ring finger, as its length could be linked to his sex drive!

The longer the fourth finger compared to the second, known as the 2D:4D ratio, the more attractive he is likely to be to the opposite sex.

Over the years, the difference between the ring finger and the index finger has been linked to everything from health problems and sperm count to aggressive behaviour, sexual orientation and sports prowess.

Now, biologists at the University of Florida have discovered that male-female ring finger proportions are tied to sex hormones in the womb -- a finding that may offer health insights.

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.

Martin Cohn, PhD, and Zhengui Zheng, PhD, of the Howard Hughes Medical Institute and the department of molecular genetics and microbiology at the UF College of Medicine, found that the developing digits of male and female mouse embryos are packed with receptors for sex hormones.

Differences in how these hormones activate receptors in males and females affect the growth of specific digits.

By following the prenatal development of the limb buds of mice, which have a digit length ratio similar to humans, the scientists controlled the gene signalling effects of androgen -- also known as testosterone -- and estrogen.

The researchers found that while more androgen equated to a proportionally longer fourth digit, more estrogen resulted in a feminised appearance.

The study uncovered how these hormonal signals govern the rate at which skeletal precursor cells divide and showed that different finger bones have different levels of sensitivity to androgen and estrogen.

"The discovery that growth of the developing digits is controlled directly by androgen and estrogen receptor activity confirms that finger proportions are a lifelong signature of our early hormonal milieu," said Cohn.

The findings appear in this week's Proceedings of the National Academy of Sciences.

Photograph: Leon Brocard on Flickr/Wikimedia Commons