May 24, 2007 The results of numeracy and literacy tests for seven-year-old children can be predicted by measuring the length of their fingers, shows new research.
In a study to be published in the British Journal of Psychology, scientists compared the finger lengths of 75 children with their Standardised Assessment Test (SAT) scores.
They found a clear link between a child's performance in numeracy and literacy tests and the relative lengths of their index (pointing) and ring fingers.
Scientists believe that the link is caused by different levels of the hormones testosterone and oestrogen in the womb -- and the effect they have on both brain development and finger length.
"Testosterone has been argued to promote development of the areas of the brain which are often associated with spatial and mathematical skills," said Dr Mark Brosnan, Head of the Department of Psychology at the University of Bath, who led the study.
"Oestrogen is thought to do the same in the areas of the brain which are often associated with verbal ability. "Interestingly, these hormones are also thought have a say in the relative lengths of our index and ring fingers.
"We can use measurements of these fingers as a way of gauging the relative exposure to these two hormones in the womb and as we have shown through this study, we can also use them to predict ability in the key areas of numeracy and literacy."
The researchers made photocopies of the palm of the children's hands and then measured the length of their index finger and ring finger on both hands using callipers, accurate to 0.01mm.
They then divided the length of the index finger by that of the ring finger -- to calculate the child's digit ratio.
When they compared this ratio to the children's SAT scores, they found that a smaller ratio (i.e. a longer ring finger and therefore greater prenatal exposure to testosterone) meant a larger difference between ability in maths and literacy, favouring numeracy relative to literacy.
When they looked at boy's and girl's performance separately, the researchers found a clear link between high prenatal testosterone exposure, as measured by digit ratio, and higher numeracy SAT scores in males.
They also found a link between low prenatal testosterone exposure, which resulted in a shorter ring finger compared with the index finger, and higher literacy SAT scores for girls.
This, says the scientists behind the study, suggests that measurements of finger length could help predict how well children will do in maths and literacy.
"We're not suggesting that finger length measurements could replace SAT tests," said Dr Brosnan.
"Finger ratio provides us with an interesting insight into our innate abilities in key cognitive areas.
"We are also looking at how digit ratio relates to other behavioural issues, such as technophobia, and career paths.
"There is also interest in using digit ratio to identify developmental disorders, such as dyslexia, which can be defined in terms of literacy deficiencies."
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