Disclaimer: this writer was born left handed and retrained to use the right hand.
For centuries, being left handed was akin to a curse. Many people even believed that being left handed was a tell tale sign of criminal tendencies, and even worse, some sort of devilish meddling.
Since time immemorial, the shame of being a 'lefty' was usually rectified by imposing a right hand only regime, to the tune of rule rapping of the knuckles, until the 'deviant' hand was forgotten.
Although most people can successfully retrain to a right hand, they do not lose the left hand brain motorial coordination. For example, a left handed person who is trained to use the right hand in writing, which is the 'sign' of righthandedness, can be easily spotted even after that change when for example she or he is stirring a pot, or unscrewing a lid on a jar. Although now using the right hand for writing, the lefty will still stir a pot in a direction counter to that of a true righty when stirring with the right hand. Same when opening a jar.
Such subtle difference in motor hand coordination are also visible when for example a person uses a tennis racquet. The lefty using a right hand to return a ball, will have weaker stroke on a straight pass than if returning the ball with a 'backhand'. Such subtleties are tell tale signs that handedness does not end at the 'hand' but that it involves a different processing by the brain in left and right handed people.
But no one, until now, knew why some people are left handed.
New research has finally uncovered the reason. Oxford University scientists, have been able to pinpoint the biological process that establish the left or right hand symmetry in the foetus.
The genes that are implicated in the process, are also believed to be instrumental in determining the differences in the left and right portions of the brain. That differentiation is what leads to right or left hand dominance.
Only about 10% of people are left hand dominant. The remainder are right handed, making the minority somehow seem lacking instead of just different.
This disparity in hand dominance is a trait peculiar only to humans.
The gene deemed to be responsible is PCSK6, which determines early on in the foetus' life, which hand one will use.
The manipulation of that gene in laboratory mice showed a disruption in left right dominance.
However, the discovery does not completely explain the development of different hand dominance. In addition to genes, environment and cultural pressure to switch to conformity, i.e. right handedness, can skew the research results.
Source : Science Daily/ 9.13.13
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