Parents may be able to predict how well children will do in math and reading by measuring their fingers, British scientists claim.
The hormones in the womb that create good math skills also make a child's ring finger longer than the index, or pointing finger, say University of Bath researchers.
It's all due to the sex hormones, scientists say. A rush of recent research suggests finger length is an index of early prenatal exposure to testosterone -- and that everything from physical aggression in men to athletic prowess in women can be predicted by digit ratios.
The more testosterone, the longer the ring finger compared to the index, the theory holds.
But testosterone affects not only forefinger length, but also how the brain develops. The "male" sex hormone is thought to encourage growth in the right half of the brain, which is associated with spatial and math skills, while slowing development in the left hemisphere, the part of the brain that deals with language.
In a study published this week in the British Journal of Psychology, the researchers compared photocopies of the hands of 75 six- and seven-year-olds (33 boys and 42 girls) in the southwest of England and measured the length of their index and ring fingers on both hands using calipers that are accurate to within 0.01 milimetres. (For those planning to try this at home, researchers measured from the bottom crease of each finger to the central tip.)
Next, they divided the length of the index finger by that of the ring finger to come up with the child's "digit ratio."
Lead author Mr. Mark Brosnan, head of psychology at the University of Bath, says a person's digit ratio is pretty much set by age five. In the adult population, the average digit ratio for females is 1.0, meaning the index and ringer finger are of the same length. For males, the average digit ratio is 0.98, meaning the ring finger is slightly longer than the index. The British study showed the average digit ratio for boys was 0.95, and 0.96 for girls.
Overall, when the team compared the children's ratios to their scores on a nationwide set of numeracy and literacy tests, they found that children with a longer ring finger (and therefore greater exposure to testosterone in the womb) were better at math than language. Children who didn't have long ring fingers were better at language than math.
When they looked at girls and boys separately, the researchers found a link between high prenatal exposure to testosterone, as measured by digit ratio, and higher math scores in males. Meanwhile, girls with shorter ring fingers (meaning low exposure to testosterone) had better literacy scores.
Finger length is by no means a measure of intelligence or ability, Mr. Brosnan stressed.
"You may well look at a finger and say, all other things being equal, they may well have a leaning towards mathematics," Mr. Brosnan says. "Or if they have a child who has a digit ratio that suggests very good verbal skills and a struggle with mathematics, this might suggest that, to explain mathematics to that child, you use a lot of verbal strategies and you cut down on the graphical, visual information."