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The area of handedness is filled with grey spots - there are no definite conclusions, nor definite proof of anything.
For the purposes of this document, being left-handed means having a preference for using your left hand for a variety of tasks, including reaching, throwing, pointing, catching. It also implies a preference for using your left footfor tasks such as kicking, as well as the preferred foot withwhich to begin walking, running and bicycling. However, there are no hard and fast rules for determining which hand or foot the Lefthander prefers to use for a particular task. Most will prefer to use the left hand or foot for delicate work. One may also have a dominant left eye, preferring to use the left eye for telescopes, camera sights, and microscopes. In general, being left-handed means having a dominant right side of the brain. Around eleven percent of Americans and Europeans are left-handed. Men are more likely (12.6%) to be left-handed than women (9.9%). People of Asian (9.3%) or Hispanic (9.1%) lineage are slightly less likely to be left-handed than whites, blacks, or North American Indians. Hand preference is usually not evident until children are age 4-6. Some children have been known to exhibit a preference as early as age 2. DeKay (1994) claims that handedness can be determined by examining ones thumbnails. The hand with the larger and squarer (is the larger thumbnail always squarer?) is supposedly the dominant hand. DeKay (1994) supports this claim with reference to the New England Journal of Medicine (presumably Block, 1974), despite the fact that subsequent articles in the same journal criticize the "thumbnail" hypothesis (Bersohn, 1974). Cats and parrots have general tendencies toward their left paws and claw; rats and monkeys tend to be right-pawed. A study of ultrasound pictures of 270 fetuses (from 1 month to 9 months) revealed that 92% sucked their right thumb while in the womb. Many scientists believe that handedness is genetic. According to this theory, left-handedness is a recessive gene, and right-handedness is dominant. This would explain why left-handedness occurs more frequently in a family where there is a background of left-handedness. A study done shows that the chance for two right-handed parents having a left-handed child is 2%. One parent left-handed and the other right-handed makes it a 17% chance, and two left-handed parents having a lefty is 46%. The human brain is divided into two hemispheres, the left and the right hemispheres. The two sides have several connection lobes that pass information between the two. The brain is thought to have great importance in the matter of hand preference. The right half of the brain is the center where the visual, spatial and intuitive processes are directed. The left half controls language, logic, and linear thinking. Both halves work together to perform whatever task is at hand. The right half has the language, logic and linear thinking ability to a much lesser degree than the left, and the left half - while it does have limited usage of visual and spatial control - is nowhere near as advanced as the right. If one side is incapacitated, and the person is young enough, he can utilize the other side in writing without much problem. It is thought that the brain is very significant in the development of handedness. Our mind is mostly contralateral. "Contralateral" means that each hemisphere controls the opposite side of the body. Our right hemisphere controls the movements of the left half of the body, while the left hemisphere controls the right half. When it comes to right or left handedness, the issue becomes more confusing. A hemisphere of the brain dominates the writing control, as well as the preferred side of action. It hasn't been fully determined what causes which side to be dominant. In any case, it is usually the case that the hemisphere that dominates the writing is contralateral. (Right-handedness is controlled by the left-hemisphere, left-handedness by the right-hemisphere). Hence the slogan "Lefties are in their right minds". However, this is not entirely correct. There is another type of control, called "ipsilateral" control. This is the "same-side" dominance. (If the left hemisphere controls the writing, the left side is preferred, if the right hemisphere controls the writing, the right side is preferred) This complicates the matter. One theory explaining left-handedness is that too much testosterone in a developing fetus slows the rate of growth in the left brain. (Keep in mind that it is usually the left brain that controls the right hand) This would mean the child has more of a chance to develop a dominance in the right-brain, and therefore be left-handed. This could explain why there are statistically more male lefties than female - obviously, testosterone is more available to male fetuses. What does left-handedness mean, practically speaking? Medical literature reports that lefties more accident prone, are more likely to have their fingers amputated by power-tools, suffer more wrist fractures. Lefties are more susceptible to allergies, auto-immune diseases, bed-wetting, depression, drug abuse, epilepsy, hypnotism, low birth weight, schizophrenia, sleeping disorders, suicide attempts, and certain learning disabilities. Lefties are six times likelier to die in an accident, and four times to likelier to die while driving. Damage to the brain, an insufficient supply of oxygen to the brain, and a difficult birth are thought to cause left-handedness. This theory has been accepted by many, as the number of lefties who fall under these categories is surprisingly high. Almost 30% of mentally retarded children are left-handed - which is three times the normal statistic for left-handedness. Twins are notorious for having difficult births, and have a high rate of left-handedness too...about 20%, which is twice the normal rate. It is also thought that the tendency to have difficult births is genetic, which would back up the statistics for left-handedness to run in the family. It is reported that over 95% of right-handers had speech localized in the left hemisphere, which is the findings of most other studies. However, it was found that 70% of the left-handers had speech located in the left hemisphere, too, instead of the right hemisphere as was expected. It should be noted that this could possibly be the result of Thomas Naglaki's theory. According to a neurological study published by Branch, Miller & Rasmussen in 1964 (Journal of Neurosurgery 21:399-405) indicates that perhaps half of all left-handers have the same left-hemisphere specialization for language abilities as do right-handers. According to Left-handers International, August 13th has been designated as International Left-handers Day.  TopBack Your comment |
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