Being Left Handed

by on March 27, 2014

in News

In the past it was thought that left-handedness is simply due to genetic causes, but recent research suggest it is not that simple. Although handedness has been studied for at least 160 years, we still continue speculate why most humans are right-handed. Meanwhile we are also gathering more and more information about the possible causes of being left-handed.

In addition to genetic causes, exposure in the womb to cigarette smoke and other toxins may contribute to left-handedness.

A study looking at the maternal health records of over 1,000 high school students born in Belgrade found that left-handed teens were far more likely to have been born to mothers who smoked while pregnant.

An Australian study of more than 50,000 identical twins done by the Queensland Institute of Medical Research found that inherited genes account for just 25% of the chance to be left-handed. The environment determined the other 75%. Although identical twins share the same genes they are not always sharing the same handedness.

Some researchers argue there is evidence for cases of left-handedness related to brain trauma before or during birth. Generally left-handed children have a history of lower Apgar scores

In his book, Right Hand Left Hand, author Chris McManus, a professor of psychology and medical education at University College London suggests that the proportion of left-handers is rising. Before 1910 only three percent of the population was left-handed. Today the incidence of being left-handed is close to 10%. McManus argues that in the past left-handers were forced to use their right hands and that in the past there was far more widespread discrimination against them.

In addition he speculates that the rising age of motherhood may also be a factor contributing to more children being left-handed. The reason why this is so, remains unclear.

The list of famous left-handed people includes individuals such as Albert Einstein, Bill Gates, Michelangelo, Rubens, Leonardo Da Vinci, Paul McCartney, Aristotle, Darwin and a number of well-know political figures (Five out of the seven most recent Presidents of the USA were left-handed; there is speculation that President Reagan used to be left-handed early in his life, but that he was forced to become right handed)

Given the disproportionate number of left-handers, some scientists have speculated that being left handed leads to being more creative. The theory is that left-handed individuals use both sides of their brain for tasks such as verbal processing, whereas right-handers use only the left side. Professor McManus’ research has identified at least 40 genes that may contribute to making people left-handed and he speculates that the genes which can determine left-handedness also govern the development of the language centers of the brain.

We sometimes refer to left-handed persons as “southpaws”. This term may have its origin from baseball. Legend has it that in the old days, ballparks were laid out with home plate to the west in order to keep the glare of the afternoon sun out of the batter’s eyes. This meant that left-handed pitchers faced the west when pitching and threw with a “southern arm”. The term supposedly originated in 1887 when it was first used in Chicago newspapers by Peter Dunne of the Chicago News.

Some sport psychologists believe that being left-handed provides an advantage to athletes—especially in sports such as baseball, basketball and tennis. Well known left-handers are Ted Williams and Rafael Nadal. It is thought that in basketball a left-handed player can surprise and confuse an opponent more rapidly by switching to the dominant hand.

A study done at the Arkansas Children’s Hospital and published in the journal Pediatrics found that left-handed children were about twice as likely as right-handed children to have been injured due to being clumsy. It is a well-known fact that left-handed individuals struggle more when using scissors, shifting gears in a car and using power tools.

Left-handed children also find it hard to write in a way that the writing does not get smudged. Typing may also be more difficult. They struggle to use scissors efficiently unless they use scissors designed for left-handed individuals.

In a Dec 2013 study published in the journal SAGE Open, Yale researchers found a four-fold increase of schizophrenia in left-handed persons. Jason Webb, an expert in child psychiatry and lead author of the study is quoted in the Daily Mail as saying “the difference is striking” The strong or disproportionate link between left-handedness and psychotic disorders remain unexplained.

According to a 1992 study in Pediatrics, left-hand dominance has been associated with disorders such as dyslexia, stuttering, autoimmune diseases and some allergies. It has been speculated that these differences are the result of influences of sex hormones on the developing cerebral hemispheres and the thymus in utero.

For more information read “Your Left Handed Child” by Lauren Milson or visit

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