Why do my hands function differently?
It is known that the most of people in the world are right-handed while only a minority are left-handed, but why does it happen? There have been made many investigations on this subject but no one knows exactly what is the reason of hand-laterality, they just propose theories about it, some of them very incredible.
One of the most incredible theories about hand-laterality is the one based on fighting. According to this theory and the evolutionary theory, left-handed people have not disappear because they are better fighters than right-handers. As there are more right-handed fighters they are used to fight against other right-handers, so left-handers have advantage in fighting because of the “surprise” factor (Chiu, par.3). But this theory is not credible since, according to the theory of evolution, the percentage of right-handers must have change and it has not.
Another incredible theory is an evolutionary theory about warriors and the position of their shield. This theory is based on the position of the heart. A right-handed warrior holds his shield with his left-hand so the heart is more protected than if he holds it with the right-hand, so the high number of left-handed deads would explain the high number of right-handed today (Kuriluk, par.3). This theory is not valuable because there has not been enough generations since the Bronze Age to make the difference and because the percentage of left-handedness has not change since the Neolithic (Raymond et al), where shields were not used.
The most credible theory seems to be the brain hemisphere division of labour theory even though it has some objections too. Both speaking and handiwork require fine motor skills. Normally, the left side of the brain controls the speaking, so the right side is free to control the handiwork. That is why most people are right-handed. According to this theory left-handers have a reversed brain division of labour. This is a very appropriate and credible theory but some left-handers use the right hemisphere to control the speaking, others use the left one and others use both, so this theory is only valid for some cases. (Holder par.4)
To sum up, nowadays there is not a definitive answer to know the differences between left and right-handers even though many different theories have been proposed.
- Holder, M.K. (2005) “What does Handedness have to do with Brain Lateralization?” Retrieved 5 May 2012 from: <http://www.indiana.edu/~primate/brain.html >
- Kuriluk, Diane. (27 Apr 2010) “What Makes People Left- or Right-Handed?” Retrieved: 7 May 2012 <http://www.ehow.com/about_6391255_people-left_-right_handed_.html>
- Chiu, Ronald. (2011) “The Fighting Hypothesis: Stability of Polymorphism in Human Handedness”. The Science Creative Quarterly. . Retrieved: 8 May 2012 from: <http://www.scq.ubc.ca/the-fighting-hypothesis-stability-of-polymorphism-in-human-handedness/ >
- Raymond, Pontier D, Dufour AB and Moller AP. (22 Dec 1996) “Frequency-dependent Maintenance of Left Handedness in Humans.” Retrieved: 7 May 2012