Left-handed people represent only 10% of the population, and it isn’t just their writing hand that sets them apart: lefties tend to be right-brain dominant, a trait that might make them more prone to fear, according to a study in the Journal of Traumatic Stress.
The study required participants to view a clip from a horror film and then recount details. Lefties were more likely to give disjointed, repetitive versions—a symptom of Post-Traumatic Stress Disorder (PTSD).
"The prevalence of [PTSD] is almost double in left handers compared to right handers,” notes Carolyn Choudhary, Ph.D., the psychologist who led the study, in an interview with The Telegraph. She adds that the right side of the brain may be more involved in the role that fear plays in PTSD.
But the same brain tendencies that might put left-handed people at risk for PTSD and other mental health challenges may also be linked to greater creativity and cognitive skills. Here’s a closer look at some more surprising facts about lefties.
The vast majority of people—especially right-handed people—have highly lateralized brains, meaning their brains strictly divide up tasks, with the left side being more active in language production and the right side controlling visuo-spatial abilities. But lefties are less likely to have such a strict division, which may put them at risk for mental health challenges like schizophrenia and ADHD.
According to a review article published by the German Medical Association (GMA), about 40% of left-hand users don’t process language exclusively on the left side of the brain. Lefties are also more likely to have a larger bridge of nerve fibers connecting the two sides, giving them greater “interhemispheric connectivity.” Researchers describe these differences as “atypical brain asymmetry”—and they may spell trouble.
Both left-handedness and atypical brain asymmetry are associated with schizophrenia, a link that was confirmed in a review of over 40 research studies. Another research paper, published in Molecular Psychiatry, found that people with a particular variant of the gene LRRTM1 are more likely to be left-handed and slightly more likely to develop schizophrenia. Fortunately, schizophrenia is rare—most lefties never develop it.
Links have also been found between left-handedness, atypical brain asymmetry, and ADHD. In a study conducted among Swedish children, left-handed kids were more likely to have ADHD symptoms, and ambidextrous subjects were at even greater risk. The researchers cautioned that not all lefties have atypical brain asymmetry, nor do all left-handed children experience mental health challenges.
The potential risks associated with left-handedness don’t end with mental health challenges—lefties may also have a greater risk of developing pre-menopausal breast cancer. A study published in BMJ found that left-handed women were more than twice as likely to develop pre-menopausal breast cancer than right-handed women.
The researchers suspect that exposure to sex hormones may influence the development of brain asymmetry and left-handedness, as well as the risk of breast cancer. Only 165 left-handed women participated in the study, so more research is needed to confirm the results.
In a world designed for right-handed people, it’s not surprising that lefties may be more accident-prone. A study on locomotive drivers in India found that 88.9% of left-handed drivers had experienced a locomotive accident, compared to only 16.1% of right-handed drivers. The design of the locomotive cabin and driving console may favor right-handed people, contributing to higher rates of accidents among lefties.
Left-handedness has its advantages, too! The same atypical brain tendencies associated with mental health challenges may also contribute to greater creativity and cognitive skills among some left-handed people.
For example, a study of professional orchestras uncovered a disproportionate number of left-handed musicians.
The GMA review article also notes that lefties are reportedly more likely to excel at music, as well as math and language fluency. Lefties are also reportedly more likely to score over 131 on IQ tests.
Some lefties also have an upper hand in sports! The GMA review article found higher rates of left-handedness among top-level athletes, especially in one-on-one sports such as tennis, boxing, and fencing.
Compared to their right-handed competitors, lefties tend to have greater ambidexterity (the ability to use both hands well). They also have more opportunities to train against right-handed competitors than right-handed athletes have to train against left-handed competitors, lending them tactical advantages in competition.
Lefties have been outnumbered since prehistoric times, according to a recent study of fossilized human remains found near Burgos, Spain. David Frayer, Ph.D., professor of anthropology at the University of Kansas and lead author of the study, determined that over 90% of people living in the area more than 500,000 years ago were right-handed.
Another recent study, from Northwestern University, explored why a small percentage of people have been left-handed throughout history. Cooperation, the researchers argue, favors people using the same hand, which makes tool-sharing more efficient. Instances of physical competition, however, favor unusual characteristics, giving lefties an advantage in sport and combat.
To test their theory, the researchers used sports data to develop a mathematical model that can correctly predict the percentage of lefties in a group—from baseball players to golfers to boxers. For example, the model accurately determined that over 50 percent of elite hitters in baseball are left-handed, while only 4 percent of successful PGA golfers favor their left hand.
The researchers also note that left-handedness can be partly attributed to genetics and partly to environment. Identical twins, for example, may favor different hands, even though they share the same genetic makeup.
The bottom line is this: as long as human societies have both competitive and cooperative aspects, lefties are here to stay.
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