Surprisingly, since 1976, Aug. 13 has been celebrated as
International Left-Handers' Day. The organization that launched this strange (some would say) holiday is called
"Left-Handers International," but despite their rather unsubtle name, they may have a point... or two.
Between
10 and 12 percent of all people are born left-handed, scientists say,
with a higher prevalence among men. While many areas of the world accept
this simple difference, other regions... well, not so much.
Surveys of Chinese students,
for instance, consistently report less than one percent to be
left-handed, leading one team of researchers to suggest it is a bias
against left-handedness, at least in part, that reduces actual as well
as reported incidence.
Whether we are right-handed, left-handed or
show no preference, one thing is clear: We are born that way.
Ultrasound recordings indicate that by week 10 of gestation, most
fetuses are moving the right arm more than the left and beginning in
week 15, most are sucking the right thumb rather than the left.
Importantly, as researchers of a
2014 study
note, this fetal behavior strongly predicts which hand will be dominant
after birth. Given these early signs, is it right to assume hand
dominance is genetic?
Causes and Complications
There is
some evidence suggesting handedness, as the scientists call it, is an
inherited trait from our parents. Still, experts estimate only about a
quarter of the variation is due to genetic influences. Interestingly,
left-handedness is believed to be linked not to one gene, but a
network of genes
that contribute to the development of left-right asymmetry in both our
bodies and our brains. However, the simple fact that about 23 percent of
identical twins are opposite-handed (so-called “mirror twins”) suggests
genes alone do not determine our handedness. Though some scientists
argue this asymmetry arises in the process of twinning itself — the
twins duke it out in the womb? — others say mirror twins prove other
factors contribute to hand preference, and there's some fascinating
evidence on their side.
For example, a Swedish
research team investigated
medical records of 6,858 men born at a hospital with ultrasound
scanning during antenatal care and 172,537 men born in hospitals without
ultrasound scanning. Based on their analysis, the researchers wrote
“the risk of left-handedness was higher among those exposed to
ultrasound” compared to those who were not and then concluded that
prenatal ultrasound must affect the fetal brain.
Another possible determinant of left-handedness may be the weather or at least linked to it.
One study
discovered “evidence of a surplus of left-handed men born during the
period November-January.” While no certain explanation can be given,
scientists suggest the link between season and hand preference might be
linked to variations in other factors, including prevalence of
infectious agents — flu germs, for instance, spread during the winter
months.
Possibly because its cause is mysterious, left-handedness has inspired the murkiest of imaginings throughout the centuries.
5 Points of Stigma
During
Medieval times, left-handedness was considered to be a sign of the
Devil, since this most evil of all demons was believed to be a lefty.
Resulting, long-standing stigmas attached to left-handedness focus on,
as might be expected, criminality, madness, and inferiority. Sadly,
Medical Daily is unable to wipe this slate entirely clean.
For
instance, left-handed people are more heavily represented in certain
groups most of us would never wish to be a part of, most notably,
pedophiles.
Past research
has associated sexual offending against children with elevated rates of
non-right-handedness. Though most left-handed people certainly are
not pedophiles,
this does mean that not only lefties but also those who lack a dominant
hand can be found tucked inside this group at proportionally higher
numbers than in the general population.
Looking at patients with
mental illness and disorders we see disproportionate numbers of lefties
once again. Previous studies have identified increased rates of
"atypical handedness" in patients with
autism spectrum disorders and also in patients with
schizophrenia. One
study
from earlier this year collected data on handedness, hospitalizations,
and severity of mental disorders for 692 children and teens referred for
psychiatric evaluation.
“Left-handedness was a phenotypic risk
factor for psychiatric disorders and increased severity of psychiatric
disorders,” the authors wrote. Specifically, left-handed children have
increased odds, by 53 percent, of being prescribed an antipsychotic drug
and increased odds, by 86 percent, of being prescribed an anxiolytic
drug. Lefties also have a 66 percent greater risk of psychiatric
hospitalizations.
According to another team of researchers, incidence of “atypical handedness” in American patients with
epilepsy
was significantly higher (17.6 percent) than in the general population.
Finally, left-handedness links to intellectual disability, as well. One
review of multiple studies,
which examined data collected from a total of 16,076 people, discovered
levels of non-right-handedness to be higher among intellectually
disabled people. Naturally, the left handed claim that, though they
swell the ranks of the disabled, they also arrive in increased numbers
among the gifted and creative. Unfortunately, the same review did not
find this to be the case.
Health and Wealth
Clearly, the weight of these assorted burdens take their toll on the health and also the wealth of left-handers.
On average, left-handed people have shorter lifespans than their right-handed peers, as this
study of women along with more
general research has demonstrated. Following such grave reports of reduced longevity, a
2014 investigation
theorized heart disease may be the underlying reason why. After tests
and analysis, the researchers discovered left-handers' heart rate
variability was significantly different from that of right-handers, and
ultimately such "atypical cerebral organization” could be related to
irregular heart function which in turn increased their risk of early
death.
Lefties come up short in another way: Their bank accounts also reveal deficits.
Research from 2014 indicates
left-handed people have 10 to 12 percent lower annual earnings than
right-handed people, on average, with greater disproportion in the
comparison of right- and left-handed women.
Now, for the Good News…
…or
at least the not-so-bad news. Perhaps to compensate for these two ills,
lefties are taking to social networking sites in droves. A
2015 online survey which
gathered responses from 3,287 participants found those who spent 30 or
more hours each week on social media were “significantly more strongly
left-handed.”
Left-handed teens are
less likely to remember their dreams
than their right-handed or mixed-handed peers, a 2014 study of more
than 3,500 children and teens proved. (Not sure if this one qualifies as
a blessing or a curse.)
Though many believe lefties are the proverbial "quiet loners," a
2013 assessment
of 662 young adults in New Zealand proved left-handers and
right-handers do not differ on any measure of the Big 5 personality
traits: extraversion, agreeableness, conscientiousness, emotionality,
and openness to experience. Interestingly, the researchers found
mixed-handers to be more introverted than either group of dominant
handers.
Last but not least, something to most definitely celebrate: A
recent study
detected an inverse relationship between ambidextrousness or
left-handedness and Alzheimer’s disease. This supports prior research
suggesting left-handed people, compared to the general population, are
underrepresented among those who develop late onset Alzheimer’s disease.
In
the end, it appears the left-handed pass through this life with greater
suffering. Why not take the day to show some love to the lefties in
your life?
Thank you to our friends at
http://www.msn.com/en-us/health/wellness/everything-you-need-to-know-about-being-left-handed/ar-BBlGQpO for this fine article. The Palm Springs Guru joins other left-handed people in today's celebration.