The Mystery of Left-Handedness

Posted on November 27, 2014

Photo: flickr

Until recently, left-handedness was a matter of great prejudice, and in many cultures, it was common to force left-handed children to write with their right hand. Throughout the world, the prevalence of left-handedness is highly variable, ranging from approximately 5% to 25% and - for unknown reasons - is more common in men than in women. So what defines our handedness? And why is being left-handed less common?

This over-representation of right-handers is regarded as an indication of a genetic component defining handedness. Twin studies have shown a higher handedness concordance rate in identical twins than in fraternal (non-identical) twins. Moreover, it has been estimated that the probability of a child being left-handed is 8% when both parents are right-handed, 22% when only one parent is left-handed, and 36% when both parents are left-handed. Interestingly, when only one parent is left-handed, there is a higher prevalence of left-handedness in children with a left-handed mother than in children with a left-handed father, indicating a possible maternal transmission.

Studies have shown that the corpus callosum, the largest structure connecting the left and right hemispheres (commissure), of left-handers tends to be larger. Therefore, this may be a sign of a greater connectivity between hemispheres and may be associated with certain cognitive skills. In fact, a greater interhemispheric connectivity could be associated with the reported observations that left-handers can have better mathematical skills or higher creativity, for example.

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Source material from The Brain Blogger

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