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 aggresssive 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.
Reading, writing and arithmetic…
In a recent study, 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.
Previously, researchers have found a link between index and ring finger lengths and homosexuality (see article in viewzone.)
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.
Ratios of 2nd digit (index finger) to 4th digit (ring finger).
Manning hasn’t yet checked the finger lengths of human dyslexics to see
whether they also point to a testosterone link. But he has already
checked out the left-handed idea, using a dexterity test. People are not
always straightforwardly right or left- handed: many have been trained
to use their right hand for writing, even if they are more skilled with
the left. So Manning and his colleagues tested how quickly 285 children
could move 10 pegs from one row of holes to another row five inches
away, using one or the other hand.
Children with low 2D:4D ratios (see illustration) are believed to
have high exposure to testosterone in the womb and are more likely to
be quicker with their left hands than the kids with higher ratios. This,
he says, suggests that our degree of left-handedness (and more
generally the way the brain divides up tasks between left and right
hemispheres) may be influenced by hormone levels in the womb.
Finger Length & Autism
Manning
has begun examining autism too. He teamed up with Simon Baron- Cohen
and Svetlana Lutchmaya from the University of Cambridge, who have used
samples of amniotic fluid to directly measure the levels of hormones
that babies are exposed to in the womb. When the children reached their
first birthday, the researchers measured their vocabularies and ability
to make eye contact. Poor language skills and an unwillingness to make
eye contact are early hallmarks of autism. They found that babies who’d
been exposed to high levels of testosterone in the womb fared the worst.
"What we’re hoping to look at is whether finger ratios can be
used as a proxy for hormones," says Lutchmaya. Amniocentesis (sampling
the amniotic fluic surrounding the unborn baby) is a risky procedure
that only a few mothers choose to undergo, she says. But by measuring
finger lengths instead, researchers can assess a random sample of
children for possible early signs of impaired language and social skill
development. Currently, they are checking the fingers of children for
whom they have amniotic samples.
Meanwhile, Manning and Baron-Cohen have looked at the finger ratios of
49 children with firm diagnoses of autism, 23 with a mild form of the
disorder called Asperger’s syndrome, and their families. The researchers
found that autistic children tended to have very low 2D:4D
ratios (see illustration). Interestingly, children with Asperger’s
syndrome had ratios that fell between those of autistics and unaffected
children. "It fits exceptionally well with the theory," says Manning.
Clearly genes play a role too in these conditions. But could fetal
hormone levels explain other cognitive differences between the sexes?
Janel Tortorice at Rutgers University in New Brunswick, New Jersey,
thinks they may. She has measured finger ratios in 2D:4D ratio
(see illustration) gay women and found that their hands were
significantly different from those of heterosexual women-in fact, they
tend to resemble those of heterosexual men.
But she has also found differences in the way these women’s brains work.
"They have more masculine fingers and more masculine cognition," she
says. On tests of spatial and verbal ability, lesbian volunteers perform
more like men than heterosexual women, she says. If this can be
confirmed by further studies, perhaps Manning’s most recent suggestion
is not as outrageous as it sounds. He claims that musical talent, too,
is nurtured in the womb.
Finger lengths foretell musical ability!
Manning recruited 54 male musicians from a British symphony orchestra. He discovered that these men had significantly lower 2D:4D
ratios than controls — they had a very "masculine" ratio. Even more
striking, when he compared the top-ranked "first" musicians with their
lower-ranked colleagues — a measure of their relative ability-the
former had significantly lower 2D:4D ratios. Could testosterone really predispose the brain to be more tuned in to music? Manning thinks so.
Musicians with short ring fingers and lesbians with long index fingers
needn’t lose heart, however. Even if fingers win a place in the pantheon
of diagnostic medicine, it’s unlikely that prospective employers or
partners will ever be able to predict our fortunes from our hands.
Tortorice reminds us that males tend to be taller than females. "But,"
she says; "we don’t use height to determine whether you’re a man or a
woman."
How well does this apply to YOUR fingers? We’d like to know.
UPDATE: 11/2009
Hormone That Affects Finger Length Key To Social Behavior
ScienceDaily (Nov. 4, 2009) — Research at the universities of
Liverpool and Oxford into the finger length of primate species has
revealed that cooperative behavior is linked to exposure to hormone
levels in the womb.
The hormones, called androgens, are important in the development of
masculine characteristics such as aggression and strength. It is also
thought that prenatal androgens affect finger length during development
in the womb. High levels of androgens, such as testosterone, increase
the length of the fourth finger in comparison to the second finger.
Scientists used finger ratios as an indicator of the levels of exposure
to the hormone and compared this data with social behaviour in primate
groups.
The team found that Old World monkeys, such as baboons and rhesus
macaques, have a longer fourth finger in comparison to the second
finger, which suggests that they have been exposed to high levels of
prenatal androgens. These species tend to be highly competitive and
promiscuous, which suggests that exposure to a lot of androgens before
birth could be linked to the expression of this behaviour.
Other species, such as gibbons and many New World species, have digit
ratios that suggest low levels of prenatal androgen exposure. These
species were monogamous and less competitive than Old World monkeys.
The results show that Great Apes, such as orangutans and chimpanzees,
expressed a different finger ratio. The analysis suggests that early
androgen exposure is lower in this groups compared to Old World monkeys.
Lower androgen levels could help explain why Great Apes show high
levels of male cooperation and tolerance.
Emma Nelson, from the University of Liverpool’s School of Archaeology,
Classics and Egyptology, explains: "It is thought that prenatal
androgens affect the genes responsible for the development of fingers,
toes and the reproductive system. High androgen levels from a foetus or
mother during pregnancy, may alter gene function and lead to subtle
changes in relative digit length and the functioning of the reproductive
system. Finger ratios do not change very much after birth and appear to
tell us something about how very early androgens affect adult
behaviour, particularly behaviour linked to mating and reproduction."
Dr Susanne Shultz, from the Institute of Cognitive and Evolutionary
Anthropology at the University of Oxford, said: "Humans are unique in
that they live in large multi-male, multi-female groups, but maintain
strong bonds and show high levels of group cooperation in both males and
females. In most other species males are competitive rather than
co-operative. Research from finger ratios may help us understand more
clearly the development of human sociality and its evolutionary
origins."
This research, published in the American Journal of Physical
Anthropology, is supported by the British Academy Centenary Research
Project, Lucy to Language — a multi-disciplinary project that aims to
understand the complexities of human social evolution.
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