Humans, just as other living creatures are symmetrical, however, not from all aspects. For example, in the embryonic phase, the heart takes the left side of the chest and starts to form; the liver develops on the right side. Brain functions are divided onto hemispheres and this also decides the right-handedness and left-handedness of the person.
In ancient times, left-handed people have often been referred to as criminals and even devil companions. Cesare Lombroso, an Italian physician and criminologist who lived in 19th century, described left-handed persons as criminals and primitive people.
In some parts of the world, left-handedness was treated as a sickness. Even several decades ago, children in some schools were trained to write with their right hand, even though they were left-handed. Thanks to the scientific evidences, the above statements sound ridiculous today.
Scientists resolved many issues regarding the cause of this variation, but some of them still remained a mystery. Domination of left or right hand has to do with the asymmetry in the functioning of the brain hemispheres. Namely, one of the hemispheres is always called dominant, and it contains areas responsible for speech. Motor nerve pathways that exit the brain are crossed, so left hemisphere controls muscles on the right side of your body and the opposite.
Scientists have found that left hemisphere is dominant in more than 95 % of right-handers, which is logical, but the left hemisphere is also dominant in about 70% of left-handers too, which is a confusing finding. Certain genes have been found more frequently in left-handed persons, so genetic background is surely the most important factor.
One of the most mysterious things which is yet to be revealed is why there are only 10 % of left-handed persons and the rest 90 % are right-handed. Variations like this are usually equally distributed in population, unless there is some specific way of genetic inheritance, which might be the case here.
Famous Left-handed People
There are many celebrities and famous people who are left-handed. You probably didn’t know that 3 of 6 previous US presidents held their pencils in their left hand (Ford, Bush, Clinton), and also the current – Obama. Among other left-handers, there are artists like Leonardo Da Vinci and Michelangelo Buonaroti, actors like Morgan Freeman and Angelina Jolie, writers like Lewis Carroll, musicians like Eminem, David Bowie, and Celine Dion, and many others.
In global, left-handed people are considered less asymmetric than right-handed people because many of them can more or less write with both hands. Researchers find this variation very interesting and even think that it can help in discovering some new facts about the complex physiology of the brain and interconnections between its left and right hemisphere.
Source and References
Source and References
Flatt, A. E. (2008). Is being left-handed a handicap? The short and useless answer is “yes and no.” Proceedings (Baylor University. Medical Center), 21(3), 304–307.
Tan U. (1989). Right and left hand skill in left-handers: distribution, learning, and relation to nonverbal intelligence. Int J Neurosci.;44(3-4):235-49.
McManus IC. (1991). The inheritance of left-handedness. Ciba Found Symp. 162:251-67; discussion 267-81.