Fertility and pregnancy * Women's health * Men's health * Sexual health

Ring finger length linked to sex hormone levels in the womb

Ring finger length linked to sex hormone levels during pregnancy May be a health indicator

Most men have a ring finger that is longer than their index finger - but for most women the opposite is true, with the ring finger longer than the index finger, and scientists have discovered the reason why.

Past studies have linked ring-to-index finger ratios with a number of traits ranging from sperm counts, aggression, musical ability, sexual orientation and sports prowess, to health problems such as autism, depression, heart attack and breast cancer.

Now a team of US scientists have discovered that finger length ratios may be determined by the levels of male and female hormones present when the embryo is developing in the womb.

Martin Cohn and Zhengui Zheng at the University of Florida investgated the development of digits in mouse embryos, which have a similar digit length ratio to humans.

By controlling the levels of male and female sex hormones - testesterone and eostrogen - they were able to look at the effect of the hormones on digit length.

When exposed to more testosterone in the womb, the 'ring' fingers of the mice were longer than their index fingers, while those exposed to the female hormone oestrogen had similar sized or shorter ring fingers compared to their index finger.

The researchers also found that the developing digits of the mice were packed with receptors for sex hormones, providing an explanation for these findings.

Commenting on the results, Dr Cohn said: "The discovery that growth of the developing digits is controlled directly by androgen (testesterone) and oestrogen receptor activity confirms that finger proportions are a lifelong signature of our early hormonal milieu."

He pointed out that the research could have wider health implications: "There is growing evidence that a number of adult diseases have foetal origins.

"With the new data, we've shown that the digit ratio reflects one's prenatal androgen and oestrogen activity, and that could have some explanatory power."

The results of the study are published in the Proceedings of the National Academy of Sciences.

This article was published on Tue 6 September 2011

Image © University College London

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