14 August 2015
Lefties often claim special skills. For example, did you know that three of the last four US presidents are left handed, as were Albert Einstein, Marie Curie, Bill Gates and Bart Simpson!
Because the brain is cross-wired to the opposite side of the body, it is often claimed that left-handedness is associated with the type of creativity sometimes associated with the right hemisphere of the brain. While there appears to be some evidence to support this, there is no evidence to support the claim that all left-handers are right-brained.
Interestingly, the incidence of left-handedness appears to be consistently around 10% of the population everywhere in the world. It is also interesting that in virtually every society left-handers have been persecuted. I recall that one of my friends at primary school in the 1960s in a small village in Lincolnshire used to get caned by our teacher if he was caught writing with his left hand. Why our teacher thought that handedness mattered and what psychotic perversity led him to believe that corporal punishment was needed to correct such a trivial matter is anyone’s guess.
So why is right-handedness more prevalent than left-handedness? The answer to this question is not known but numerous theories exist ranging from hemispheric lateralization in the brain to genetic factors. Interestingly a study of ultrasound scans of human foetuses in 1991 found that at 15 weeks most foetuses prefer to suck their right thumb, hinting that handedness is present prior to birth. Interestingly, Hepper et al. followed up this study of 75 individuals. They found that the 60 foetuses that preferred to suck their right thumb were indeed right-handed as teenagers, and of the 15 foetuses that preferred to suck their left thumb, 5 were right-handed and 10 were left-handed.
Whether handedness is an inherited genetic trait or not is also not known. In 1991 Robert Collins of the Jackson Laboratory attempted to breed left- or right-handed mice. Since the attempt failed it suggests that handedness is not inherited. However, the study did find that left or right paw dominance was associated with higher levels of dopamine in the corresponding hemisphere, leading to suggestions that physiological and neurological lateralisation are associated.
Left Handers’ Day may seem like a bit of a gimmick, but as a result of highlighting the plight of left handers many things have improved. For example, whereas once items such as can openers, scissors and computer mice were only available in right-handed versions, today many more products are designed to be ambidextrous.
To find out more about Left Hander’s Day visit www.lefthandersday.com.
Posted by Alistair Schofield at Friday, August 14, 2015