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 ComplicationsThere 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 StigmaDuring 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 WealthClearly, 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.