Your finger length can predict how you will do on various tests in school. They can also tell if you are likely to be homosexual or straight, if you will likely get certain cancers, be a musician, writer or a scientist, or if you will have an aggressive or passive personality.The two fingers that are important are the index finger -- the one you use to point to something -- and the ring finger.
In a recent study from the help of online universities, the results of mathematics and literacy (reading) tests for seven-year-old children could be predicted by measuring the length of these two fingers.
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 estrogen in the womb -- and the effect they have on both brain development and finger length. This is nothing new, since scientists have known for many years that elevated levels of testosterone -- or other hormones closely resembling testosterone -- can cause the brains of both males and females to be more "masculine."
It has long been known that boys tend to do better on math tests while girls do better at writing, reading and verbal tests.
"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.
"Estrogen 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."
How they did the research
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 math skills relative to reading and speaking skills.
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 [fear of science], and career paths.
There is also interest in using digit ratio to identify homosexuality, developmental disorders, such as dyslexia, which can be defined in terms of literacy deficiencies, and aggressive vs. passive personalitity traits.
Other interesting observations about finger length:
Bodily characteristics that develop in distinctly masculine and feminine ways are usually the product of sex hormones. Some features differentiate at puberty, such as breasts, muscle development and jaws. But other sex differences are already set by the time we're born, relative finger lengths among them, and seem to be the result of fetal androgens (hormones such as testosterone or related hormones) masculinising the males. some of those hormones come from fetal testes and adrenal glands, the rest make it across the placenta from the blood of the mother. But exactly how much comes from whom -- and what alters the balance -- are still not entirely understood.
"Prenatal development is a black box," says John Manning of the University of Liverpool. He is one of a small number of scientists beginning to wonder if fingers could be used as a way of peering into that "box."
Finger lengths may predict cancer!
In a paper just published in the journal Medical Hypotheses (vol. 54, p 855), Manning highlights conditions such as heart disease, breast cancer, autism and dyslexia. Both heart disease (in men) and breast cancer have been linked with high levels of the female hormones Eestrogen and Progesterone. Most of the studies of this link have looked at circulating levels in the adult, but evidence is mounting that too much of the wrong hormone in the womb, before birth, may be the real culprit.
Oimitrios Tricopouos, an epidemiologist at Harvard University, proposed a decade ago that breast cancer may originate in the uterus of the mother (The Lancet, vol. 335, p 939). He suggested that high concentrations of estrogen may create a "fertile soil" for cancer to develop later in life. He also thought that variability in estrogen levels during pregnancy may help to explain why breast cancer rates are generally higher in women born to Caucasian mothers compared with those born to Oriental or younger mothers. Recently he and his colleague Karin Michels showed that high birth weight in girls-another sign of high prenatal estrogen levels-was associated with an increased risk of breast cancer.
If high estrogen levels are indeed to blame, Manning thinks that high 2D (see illustration) ratios could be used to identify women who are at increased risk of breast cancer. "I don't know of other sexually dimorphic traits that are so stable," he says. "That's what makes it so exciting." He interviewed 118 women in a breast cancer clinic, measured their finger lengths and noted how old they were when the first tumour appeared. "It was earlier if there was a higher ratio," he says.
Finger length linked to left-handedness!
The developing brain is also sensitive to hormones in utero. Knowing this, Norman Geschwind and his graduate student Albert Galaburda, now at Harvard Medical School, made a controversial claim in 1985. They suggested that prenatal testosterone slows the growth of certain areas of the left hemisphere and facilitates the growth of corresponding regions of the right hemisphere. At the time they wondered whether testosterone was partly to blame for such things as left-handedness, dyslexia and autism (Archives of Neurology, vol43,p 428).
Galaburda and his colleagues have since developed a way to induce selective brain damage to the frontal lobe of newborn rats to mimic some of the symptoms of dyslexia. Curiously, while male rats with this kind of damage have trouble responding to rapidly changing sounds -- much like dyslexic humans -- females don't. "We induce the malformations in males and females," he says, "but only the males have trouble."
It is clear that there is a "genetic component" to dyslexia. But Galaburda thinks fetal testosterone plays a role too by reducing plasticity in the young brain, making males, susceptible to brain malformations that females manage to overcome.
Intriguingly, when female rats are given extra testosterone, they too show signs of dyslexia.