Nature or Nurture, Blessing or Curse?
By Molly Kalafut
This is a paper I wrote in the early 1990s on the subject of left-handedness. Since that time there have been changes and updates in the field. When I have time I hope to update this information considerably.
Around ten percent of Americans are left-handed, and of those, there are twice as many lefty males as females. 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.
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 and 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.
Background Information on Handedness
Prejudices against left-handers abound, for throughout history, lefties have been considered inferior. Centuries ago, the Catholic Church declared left-handed people to be servants of the Devil. For generations, left-handers who attended Catholic schools were forced to become right-handed. Only a few decades ago in Japan, left-handedness in a wife was sufficient grounds for divorce. The wedding ring is placed on the left hand in order to chase away evil spirits that may haunt the marriage. In Arab nations, the right hand is used to touch parts of the body above the waist, while the left hand is used for below the navel. Bedouins segregate the women to the left side of the tent to keep the right side free for the men. (Making it fairly obvious to determine which gender is considered more important.) Natives on the Guinea coast never touch their left thumbs to their beer mugs, in the belief that it would poison the beverage. Maori women weave ceremonial cloth with the right hand, because to use the left hand would profane and curse the cloth - the penalty for using the left hand is death. African tribes along the Niger river do not allow their women to prepare food with the left hand for fear of poisonous sorcery.
Religion has played an important part in oppressing the image of the left hand. In Matthew 6:3 of the Bible, Jesus instructed his followers that when they do charitable things, to "not let thy left hand know what thy right hand doeth." Jesus also expressed the following sentiments regarding the Judgment Day. "And before Him shall be gathered all nations; and He shall separate them one from another, as the shepherd divideth his sheep from the goats; and He shall set the sheep on His right hand, but the goats on the left. Then shall the King say unto them on His right hand, 'Come, ye blessed of my Father, inherit the kingdom prepared for you from the foundation of the world...' Then shall He say into them on the left hand, 'Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels...' In the Old Testament, God told Jonah the wicked city of Nineveh contained people so sinful they "cannot discern between their right hand and their left hand," leaving us to infer that they cannot discern between good or evil. Greeks, in their worship of Zeus, posted sentries to watch people entering the holy temples and make sure they entered with their right foot, because entrance with the left foot was thought to curse the building. Also, the Greeks took care to never put their left leg over the right while crossing their legs. In Hindu rituals, followers are required at times to circle people and/or objects three times, from left to right to cleanse them.
Even languages from around the world show how civilizations prefer the right over the left. The word "left" comes from an Old English word meaning "weak" or "worthless" The Italian word "mancino" is translated to "deceitful"...as well as "left". "No ser zurdo" is a Spanish phrase meaning "to be very clever", which is literally translated to mean "not to be left-handed". In English, the word "adroit" is commonly used to mean "proper" or "correct". In French, the word "adroit" means "right". The English usage of the word "gauche" is accepted as meaning "clumsy", or "awkward". In French, it is translated to mean "left". Our word "dexterous" comes from the Roman word "dexter", which in turn means "right". The Roman word for "left" is "sinister", and the phrase meaning "masturbation" is translated to "left-handed whore". "Linkisch" is German for "awkward" and "left".
Theories For Handedness
For years, mankind has been searching for the answers to why people prefer one hand over the other, why the majority of people choose the right hand, and why the left hand is chosen in such a minority. Handedness is not fixed at birth. It usually just develops, and is malleable to outside conditions. While some postulate that there may be a genetic predisposition to left-handedness or right-handedness, handedness is definitely subject to change due to the environment.
Plato was one of the first documented people to come up with an explanation for why people are either right or left-handed. He suggested that mothers and nurses carried their children in their left arm so they could use their right hand for other tasks. The child therefore clings to her mother with her right hand. This develops the child's left-hand ability, because that is the hand free for the child to use in exploring her surroundings. Hence, she is left-handed. This theory has no credibility, however. The children who were raised to be left-handed would then reverse the process by carrying their children in the right arm, which according to Plato's theory would make them right-handed. Were this theory correct, the proportion of lefties and righties would switch each generation.
Another theory for why people usually develop a preference for one hand is one that refers to our ancient ancestors. Long ago, life or death situations were faced regularly, so much so that instinct and automatic reactions were necessary for survival. With practice, developing a specific hand would make it react swiftly and automatically. This took less time than if the brain had to decide which hand to use. Tools and weapons were cherished possessions in the early times, and usually handed down from generation to generation. If the tool was designed for the right hand, the children who inherited it would have to learn to use it right-handed. It is thought that this hand-preference stimulated a dominance in the brain. Eventually, as humans became more specialized in their speech abilities, a language dominance occurred in the part of the brain that controlled their preferred hand.
A theory that was advocated in the nineteenth century was one relating to handedness stemming from a military background. For several millennia, fighting was an important part of life, and most men were given some background in the use of the sword. It is easier to strike an enemies heart by holding the sword in the right hand, since the heart is shifted towards the left side of the body. It was suggested that this stimulated the brain for a predisposition towards right-handedness. This view loses it's credibility, considering that it would mean the ones who did the fighting (in almost all cases men) would be righties, while the ones who were not instructed in swordplay (women) would be equally left and right-handed. Statistics show, however, that men are three times more likely to be lefty than women. Not only that, but medical doctors claim that the shift of the heart is of too little consequence to be a factor.
Another theory for handedness is related to the last one mentioned. Most soldiers hold their shield with their left hand to protect their heart while engaged in battle, and thus use their right hand to hold their weapon. This does not explain left-handedness, nor the high incidence of right-handedness before the shield was invented.
Those last few theories were ones that are rather obsolete. The next two theories that shall be presented are ones that are currently held as very possible and likely.
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 scientist Marion Annett believes most individuals have a "right shift" factor. This factor disposes it's carrier to be right-handed. When the gene is absent, the individual may be either right-handed or left-handed. She studied this theory by interviewing children whose parents were both left-handed. Since the parents were left-handed and therefore lacked the right-shift factor, the children would not have it either. She studied the speed with which the children could perform a peg-sorting task. The results showed that 50% did better with the left hand, and 50% did better with the right. These results back up her prediction that the hand preference of those without the factor would be determined by chance.
The Effects of the Brain on Handedness
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.
The brain is not yet fully understood. Many of the theories presented contradict one another and give differing numbers. The numbers produced in one theory may be totally opposite that of another. All the thoughts produced in this section are possible, though none are accepted as absolute fact as of yet.
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.
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.
There is a test that is believed to determine hand preference and hemisphere dominance, called the Torque Test. One draws one's name with one hand, and then circles it. Then one draws the name with the other hand, and circles it. The hand that produced the best handwriting is the hand of preference, and the if the circles were drawn clockwise the right-brain is dominant, and counterclockwise circles indicate a left-brain dominance. One circle clockwise and the other counter-clockwise shows mixed dominance.
Recently, breakthroughs were made by way of medicine. A dosage of sodium amytal temporarily anesthetizes one hemisphere of the brain at a time, which allows surgeons to find out which hemisphere controls language. 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.
To confuse the issue even more, another factor has been thrown into the argument. Some left-handers write with their pencil facing the bottom of the page, in a "hooked" position. This is called inverted writing. Jerre Levy and MaryLou Reid think that the inverted lefties have their speech control in the left-hemisphere control, the same hemisphere as non-inverted right-handers. Non-inverted lefties are dominant in the right hemisphere like inverted righties. The lefties and righties are mirror images of the other. The findings result in 70% of left-handers and 99% of right-handers are controlled by the left hemisphere. These happen to be the exact findings of the sodium amytal procedure.
The area of handedness is filled with grey spots - there are no definite conclusions, nor definite proof of anything. The only fact is that for some reason, 10% of the world's inhabitants prefer to use the left hand over the right hand. In trying to explain this, the reasoning behind handedness center around protection, convenience, genetics, environment, brain hemisphere dominances, birthing process, and effect of body chemical levels. Which one is right? At this point, it's hard to tell. Researchers have been reluctant to explore this realm, because of the endless contradictions in numbers that result. Perhaps in the future, a method will be found to conclusively give an answer to the question of why left-handers are who and what they are.
(Warning: I may have cited the page numbers wrong on one or two of the magazine articles - I hope to track them down and correct them eventually.)
Copyright 2005, 2006, 2007, 2008 and beyond! By Molly Kalafut