From the archive, originally posted by: [ spectre ]


One Election Outcome Certain: A Lefty Will Win White House
BY Russell Berman  /  June 23, 2008

WASHINGTON — While this year’s presidential campaign has been marked
by historic firsts, the nominations of senators McCain and Obama will
renew one surprising trend: For the fifth time in the last 35 years,
America will have a lefty in the White House. Both major party
candidates are southpaws, contributing to a largely unexplained
phenomenon that has vexed researchers and historians — and drawn
notice from a federal judge destined for the Supreme Court. Though
left-handers comprise just 10% of the population, they are dominating
presidential politics.

Their recent success transcends ideology. Since 1974, presidents Ford,
Reagan, George H.W. Bush, and Clinton have all favored their left
hands, while President Carter and the current President Bush are
righties. The trait is also not exclusive to winning candidates: Vice
President Gore is left-handed, as are past presidential contenders
Robert Dole, John Edwards, Bill Bradley, and Ross Perot. A prominent
New Yorker who flirted with a White House bid, Mayor Bloomberg, is a

Researchers who have studied handedness have found links to genetics
and to brain function, but there is no prevailing theory to explain
the plethora of left-handed commanders in chief in recent decades. Yet
the trend is more than a statistical anomaly, a professor of neurology
and psychiatry at the University of California Los Angeles School of
Medicine, Daniel Geschwind, said. “It’s definitely not an accident.
The chance is less than one in a thousand,” he said.

Before 1974, just two presidents were known definitively to be left-
handed: James Garfield and Harry Truman. Studies have shown that
whereas righties favor the left hemisphere of their brain, which
controls language, left-handers are more likely to have bilateral
brain function, which could allow them to visualize problems more
broadly and with more complexity. A higher percentage of
mathematicians and scientists are left-handed, and the same is true
for artists. Bilateral brain function could relate to the social and
interactive skills needed to be successful in politics, but not enough
research has been done, Dr. Geschwind said.

Left-handedness also has proved a distinct advantage in certain
sports, including tennis and baseball, where southpaws are prized both
in pitching and batting. At the same time, studies have suggested an
increased prevalence of schizophrenia, autism, and bipolar disorder
among left-handers. Twins are more likely to be left-handed, research
shows, and handedness has tended to run in families, although that was
not the case for the elder Mr. Bush, a lefty, and his son George W., a

A scientist at the National Cancer Institute, Amar Klar, has found
another, more novel trait that may distinguish left-handers from right-
handers: hair growth. “Handedness is related to the way the hair spins
on the back of your head,” he said in an interview. His research shows
that the whorl for right-handers curls clockwise in 92% of cases. In
left-handers, the distribution is random, with half exhibiting a
clockwise whorl and the other half spinning counterclockwise. Mr. Klar
said he could spot a counterclockwise whorl from seeing Mr. McCain and
Mr. Clinton on television and looking at the way they appear to comb
their hair.

Researchers have long debated why left-handers have succeeded as a
distinct minority group in a society dominated by right-handers.
“People like to think there’s something wrong with left-handers,” a
professor of psychology at University College London who has written a
book on handedness, Christopher McManus, said. Yet the percentage of
left-handed people across the population has remained stable at
between 8% and 10%, a statistic that stands in contrast to other
animal species and argues in favor of certain advantages to being left-
handed. “Something is keeping 10% of the population there,” he said.

One theory to explain the success of left-handers in politics is that,
at an early age, they recognize that they are different in a
fundamental way from most of their peers, said Melissa Roth, the
author of “The Left Stuff: How the Left-Handed Have Survived and
Thrived in a Right Handed World.” “Their difference might be treated
as a positive or a negative, a ‘creative’ asset or a failure to adapt,
but either way they are aware that they are ‘special,’ and that’s a
trait psychologists find in many leaders,” Ms. Roth said.

Still, some contend that the phenomenon of left-handed presidents is
no more than a blip. An associate justice of the Supreme Court, Samuel
Alito, even offered that argument — and drew criticism for doing so —
in dissenting from a ruling that overturned a murder conviction of a
black man who had been tried before an all-white jury. Justice Alito,
then a member of the 3rd U.S. Circuit Court of Appeals, took issue
with a majority opinion that said “an amateur with a calculator” could
have figured out the appropriate percentage of black jurors in the
county where the case was tried. “Although only about 10 percent of
the population is left-handed, left-handers have won five of the last
six presidential elections,” Judge Alito wrote. “Our ‘amateur with a
calculator’ would conclude that ‘there is little chance of randomly
selecting’ left-handers in five out of six presidential elections. But
does it follow that the voters cast their ballots based on whether a
candidate was right- or left-handed?” The judge did not mention that
in at least two of those elections — 1992 and 1996 — the voters did
not have much of a choice: As in the coming election, the leading
candidates were all left-handed.

They May Have Higher Health Risks, But Lefties Enjoy Element of Surprise
BY Amanda Onion  /  Feb. 17, 2005

It’s not easy being a lefty. Statistics show left-handed people are
more likely to be schizophrenic, alcoholic, delinquent, dyslexic, and
have Crohn’s disease and ulcerative colitis, as well as mental
disabilities. They’re also more likely to die young and get into
accidents. So if evolutionary theory dictates survival of the fittest,
why do lefties still exist? According to new theories, what left-
handed people (and other animals) may lack in fitness, they make up by
being different.

Researchers in France recently took an interest in the
disproportionately high number of left-handed athletes who thrive in
sports involving direct one-on-one contact, such as baseball (think
Babe Ruth), tennis (think John McEnroe) and boxing (think Oscar de la
Hoya or the fictional Rocky Balboa). Charlotte Faurie and Michel
Raymond of the University of Montpellier in France figured the same
reason so many left-handed people are successful in such sports could
also explain a possible higher success rate among lefties in primitive
combat. This means that, back in the days when fighting was an
important part of survival and winning mates, the rare left-hander may
have come out on top more often.

Watch That Left Hook

Here’s the thinking: Most left-handed people would be practiced in
fighting right-handed people (since right-handed people make up the
majority), while most right-handed fighters would not be as prepared
to fight someone who favors their left side. Advantage: lefties. “The
fact that left-handers are less common means they have a surprise
effect,” said Faurie.

To prove their theory, Faurie and Raymond surveyed nine primitive
societies in five separate continents. Through a mix of direct
observation and existing data, they estimated the number of left-
handed people within each population. They also looked at murder
rates, thinking that those communities with higher murder rates might
favor populations with more left-handed people. The more violence, the
more chances lefties would have at issuing their unexpected left hook,
or other such weapon, and come out on top.

Among these samples, they found strong support for the idea that, at
least in primitive societies with higher levels of violence, lefties
thrive. For example, when they singled out the Dioula of Burkina Faso
in West Africa, where the murder rate was only 0.013 murders per 1,000
residents each year, they found only 3.4 percent of the population
were left-handers. Data from the Eipo of Indonesia, meanwhile, where
there are three murders per 1,000 people each year, show 27 percent of
the population is left-handed. Other research is suggesting that
humans aren’t the only species who have minorities of certain side-
favoring individuals. The equivalent of lefties has been observed in
chimpanzees, toads, even among schools of fish.

Favoring one side — a result of something called lateralization of
the brain — was once thought to be a uniquely human trait linked to
language. The ability to speak comes mostly from left regions of the
brain, so the assumption was this would correspond with increased
motor control on the opposite, or right side. In motor control,
activity on one side corresponds to the opposite side of the brain. So
this could explain why about 70 percent to 90 percent of people are

But lately, researchers who study animals have been poking holes in
that idea. William Hopkins, a psychologist at Emory University’s
Yerkes National Primate Research Center, has found most chimpanzees
use their right hands for a number of functions, from throwing a ball
to scooping peanut butter from a tube. Furthermore, he and his
colleagues have linked this handedness to the KNOB, an area of the
brain associated with motor activity, not language. Hopkins further
points out that chimps don’t have language, so why would there be a
majority of right-handed chimps? As among humans, being in a minority
when it comes to handedness has its advantages. “The advantage is at
the individual level,” said Giorgio Vallortigara, a psychologist at
the University of Trieste in Italy. “The advantage is observed only
until the minority group remains a minority. If the number of
individuals that do not share the side preference that most do
increases, then the advantage is lost.”

Swimming Their Own Way

Vallortigara has studied how this works in certain schools of fish.
Some fish swim in large groups, or shoals. Traveling in a pack
provides individuals with extra protection from predators. Most of the
fish in the group share the same tendency to keep an eye out on one
side or the other for predators and to flee in a particular direction
if a threat is seen. Minority-sided fish, meanwhile, are likely to
watch the other way and turn and flee in the opposite direction. While
these fish miss out on the protection of the group, they gain the
element of surprise — predators don’t expect them to turn in the
opposite direction from the group. Similar examples can be found among
birds and toads. In each case individuals that favor an unusual side
find some benefit, be it surprising predators with the direction of
their flight or by finding resources that might elude the majority.

Still, researchers point out that, at least among humans, genetics is
not the only factor behind left-handedness. Evidence has shown a link
between trauma during gestation or during birth, as well as in the age
of the mother and so-called pathological left-handedness. Numbers show
that mothers who are over 40 at the time of their child’s birth are
128 percent more likely to have a left-handed baby than a woman in her
20s. “Handedness is controlled by a whole lot of pathways in the brain
and if any one of these pathways is mucked up during gestation, then
handedness becomes a cosmic dice game,” said Stanley Coren, a
psychologist at the University of British Columbia and author of “The
Left-Handed Syndrome.” “We believe this accounts for about half of all
left-handers.” It could be that this early trauma is also the trigger
behind health problems linked to left-handedness. Coren points to two
famous left-handers, Presidents Bill Clinton and George H.W. Bush, as
evidence. Both had histories of birth stress and have health issues
from Clinton’s severe allergies to Bush’s Graves’ disease.

Then again, as many lefties might point out, being left-handed can
also offer intellectual prowess. Tests conducted by Alan Searleman
from St Lawrence University in New York found there were more left-
handed people with IQs over 140 than right-handed people. Famous left-
handed thinkers in history from Albert Einstein to Isaac Newton to
Benjamin Franklin seem to underline the point. As Hopkins says, it may
be that left-handed people occupy the extremes when it comes to health
and ability. “The anomaly is left-handed people make up the extremely
gifted and the extremely compromised,” said Hopkins. “The rest of us
make up the middle ground.”

Left-handers win in hand-to-hand combat
BY Will Knight  /  08 December 2004

Left-handed people may be better equipped for close range mortal
combat than those who rely on their right hands, according to

Charlotte Faurie and Michel Raymond of the University of Montpellier
in France examined the number of left-handed people in
unindustrialised cultures as well as the homicide levels within each
culture. They discovered a correlation between levels of violence and
the proportion of the left-handed population – the more violent a
culture, the higher the relative proportion of left-handers. The cause
for this, the researchers suggest, is that left-handers are more
likely to survive hand-to-hand combat. The news could provide comfort
for those who routinely struggle with right-handed scissors and can-
openers, but some experts are unconvinced by the link.

Left-handed people are more prone to some health problems, suggesting
the trait ought to disappear naturally over many generations through
natural selection. But left-handers continue to make up a small
proportion of the human population, hinting there could also be some
evolutionary advantage to being left-handed. And the ratio of left-
handers to right-handers is higher in successful sportspeople than it
is in the general population, suggesting there is definite advantage
to favouring the left hand or foot in competitive games, such as

Homicidal tendencies

“Because of the advantage in sports we thought there could be a
similar advantage in fights,” Faurie told New Scientist. The theory is
that right-handed competitors are less accustomed to facing left-
handers, making them a more difficult proposition. Faurie and Raymond
studied several unindustrialised societies with varying rates of
homicide, using their own fieldwork and ethnographic literature. They
excluded industrialised cultures due to a lack of data and because,
they argue, use of firearms is unaffected by handedness. At one end of
the scale, their sample included the Dioula of Burkina Faso, where
just 3.4% of the population is left-handed and there are only 0.013
murders per 1000 inhabitants each year. At the other end of their
sample spectrum, they studied records of the Eipo of Indonesia, where
27% of the population is left-handed and the homicide rate is
considerably greater – three murders per 1000 people each year.

The strong correlation between the proportion of left-handers and the
number of homicides in each culture suggests that left-handers are
more likely to survive a fight, they say. “It could be one of the
reasons left-handedness has survived,” Faurie says. “Though there may
be other reasons too.”
Brain differences Daniel Nettle, an expert in human evolutionary
history at the University of Newcastle-Upon-Tyne, UK, is intrigued.
“The results quite surprised me,” he says. “But I can’t think of any
reason why they might be an artefact [of the study design], so it
looks like an interesting finding.”

However, Chris McManus at University College London, who has
researched handedness, is more sceptical about the link. “I’m far from
convinced,” he told New Scientist. “I don’t think it is anything as
simple as this.” McManus says the sample data is too small provide
firm evidence of a connection between handedness and fighting prowess
and says data from western societies should also have been included.
He believes the success of left-handers may be largely due to
differences in the brain. “It may be that sometimes their brains
assemble themselves in combinations that work better for certain
tasks,” he says.

Journal reference: Proceedings of the Royal Society B (DOI: 10.1098/

Charlotte Faurie
email : c.faurie [at] [dot] uk

Michel Raymond
email : raymond [at] isem [dot]

“Behavioural asymmetries are observed in many animal species. In
humans, for manual activities, individuals exhibit a preference for
one hand. This polymorphism is present in all current human
populations. Handedness is a heritable trait, and its determinism is
partially genetic. Right-handers are more frequent than left-handers
in all the populations so far investigated. Handedness is not a
neutral trait. Left-handedness is associated to several selective
disadvantages (reduced longevity, lower birth weight, increased risk
of many health disorders). However, the polymorphism has been
maintained at least since the upper Palaeolithic.

We have tested two hypotheses, based on frequency-dependant selection
mechanisms (advantage of the rare) to explain this phenomenon: 1) left-
handers would have persisted because of a strategic advantage in
fighting interactions; 2) left-handers would have a social status
advantage (social status is one of the components of the selective
value). A frequency-dependent advantage of left-handers has been shown
in interactive sports, which are similar to ritualised fights.
Comparing eight traditional societies, we have demonstrated that the
incidence of left-handedness is positively correlated with the
prevalent rate of homicides. Moreover, we have found a reproductive
advantage of sport competitors in the French population. These results
reinforce the hypothesis of an advantage in fights, and underline its
importance for the evolution of the polymorphism of handedness.

We have shown associations between socio-economic status and
handedness in a population of children and in two large cohorts of
adults in France. Finally, we have compared left- and right-handers
for some estimators of the reproductive value, in the two French
cohorts, in a population of hunters-gatherers in Gabon and in a rural
population in Dominica. The results are discussed in the general
context of the evolution of handedness in humans.”


The human brain is a paired organ; it is composed of two halves
(called cerebral hemispheres) that look pretty much alike. The term
brain lateralization refers to the fact that the two halves of the
human brain are not exactly alike. Each hemisphere has functional
specializations: some function whose neural mechanisms are localized
primarily in one half of the brain. In humans, the most obvious
functional specialization is speech and language abilities. In the
mid-1800s, Paul Broca (a French neurosurgeon) identified a particular
area of the left hemisphere that plays a primary role in speech
production. Shortly afterwards, a German neurologist, Carl Wernicke,
identified another part of the left hemisphere primarily concerned
with language comprehension.

Most humans (but not all) have left hemisphere specialization for
language abilities. The only direct tests for speech lateralization
are too invasive to use on healthy people, so most of what we know in
this area comes from clinical reports of people with brain injuries or
diseases. Based on these data, and on indirect measures, we estimate
that between 70% to 95% of humans have a left-hemisphere language
specialization. That means that some unknown percentage of humans
(maybe 5% to 30%) have anomalous patterns of specialization. These
might include: (a) having a right-hemisphere language specialization
or (b) having little lateralized specialization. The more one knows
about the neurological mechanisms underlying language abilities, the
more complicated these issues become. For instance, some language
functions (like prosody– the emotive content of speech) is
specialized in the right hemisphere of people with left-hemisphere
language specializations. The bottom line is that, despite overly-
simplistic descriptions of left-brain / right-brain stuff one finds in
introductory textbooks and the public press, there is still a great
deal about brain lateralization that we simply do not yet understand.

What Is Handedness?
“Handedness” is a vague term, and can mean many things to many people.
Most people in our society define handedness as the hand you use for
writing. Within the scientific community, the vagueness of this term
has led to much debate. Researchers define handedness based on
different theoretical assumptions. For instance, some define
handedness as (a) the hand that performs faster or more precisely on
manual tests, while others define it as (b) the hand that one prefers
to use, regardless of performance. Some think that there are two types
of handedness: (a) either left or right, or (b) either right or non-
right, while others think there should be three categories (to include
ambidexterity). Some think there are two different kinds of
ambidexterity. Some think that handedness should not be lumped into 2
or 3 or 5 categories, but rather measured along a scale of a
continuum. These are just examples of a few of the differing criteria
for handedness! My work attempts to resolve some of these issues.

What Does Handedness Have To Do With Brain Lateralization?
The same chap that identified a region of the brain specialized for
language Paul Broca (Paul Broca) also suggested that a person’s
handedness was opposite from the specialized hemisphere (so a right-
handed person probably has a left-hemispheric language
specialization). But the kick is: this is not a mirror correlation
(that is, a majority of left-handers also seem to have a left-
hemispheric brain specialization for language abilities). Tricky
business, eh? For over 150 years, many researchers have been trying to
figure out this robust-but-imperfect correlation between handedness
and brain lateralization. We are still trying.

Who Cares?
The primary historical reason that the hand-brain link was considered
important and became a generally-accepted methodology, was because for
nearly a century it was the only hint that a neurosurgeon had prior to
surgery which hemisphere was specialized for language. Clinicians used
handedness as a marker for brain lateralization until the Wada (sodium
amytal) Test was introduced in the 1960s.

Ambidextrous tendencies may mean better memory
BY James Randerson  /  22 October 2001

Having a close left-handed relative makes right-handers better at
remembering events than those from exclusively right-handed families,
new research suggests. There is a downside, however, as members of
these ambidextrous families may be relatively impaired in their
ability to recall facts. According to the study, having a left-handed
sibling or parent means the organisation of your brain is intermediate
between a pure ‘lefty’ and a pure ‘righty’. Specifically, Stephen
Christman and Ruth Propper at the University of Toledo, Ohio claim
that people with ‘lefties’ in the family have a larger corpus callosum
– the connection between the brain hemispheres. This makes you better
at certain memory tasks, but worse at others, they believe.

Two types of memories are involved. Episodic memories are those with a
context that is separate from the information itself – for example,
where you parked your car or where you left your keys. Semantic
memories on the other hand are things ‘you just know’, such as the
dates of the First World War or the recipe for apple pie.
Filling the gaps The researchers showed 180 right-handed subjects
lists of words. Some of this group was asked to recall as many of the
words as possible once the list had been taken away. This tests
episodic memory because the subjects have to remember the words they
were taught. Others from the group were given fragments of words with
a letter missing and asked to fill in the gaps. This semantic test
simply relies on knowing how the correct word should be spelt.
Subjects with close left-handed relatives did better at the first
‘remember’ task, but worse at the second ‘know’ task. “The key
difference is not whether you are right handed, but whether you are
strongly or weakly handed,” explains Christman.

Making the connection

A definitive explanation for the results is still some way off, says
Christman. But he suspects that it might involve the roles that
different brain hemispheres play in memory. He believes the
information itself tends to be stored in the left hemisphere, while
the place and time context resides in the right. Both these components
will be useful in episodic memories, so he suspects that people with a
large corpus callosum linking their hemispheres – such as those from
more ambidextrous families – will do better at these tasks. Semantic
memory requires only one hemisphere, so it may be that those with
fewer connections between the hemispheres have less interference and
perform better. Chris McManus, an expert in handedness at University
College London, agrees that people with left-handed relatives have a
brain that is “slightly more like that of a left-hander”. But he is
sceptical about Christman’s explanation. The link between a weak-
handedness and a large corpus callosum is “distinctly controversial”,
he says.

Journal reference: Neuropsychology (vol 15 (4))

Stephen Christman
email : Stephen.Christman [at] utoledo [dot] edu

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