Curious1
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The true causes of being left-handed or right-handed is unknown to science, but several theories exist as to why people favor one hand over the other. Scientists and doctors who study the subject can be placed in one of three categories: those who believe handedness is genetic, those who believe it is developmental, and those who believe it is a combination of both. One doctor, Amar J. S. Klar, has developed a genetic hypothesis that explains why there are more right-handers than lefties, and why left-handed parents have higher rates of having left-handed children. Dr. Klar stipulates that “normal” people have a gene that makes them right-handed by default. The people with this gene account for about 80% of the population. The other 20% lack the right-handed gene, but lacking the gene doesn’t necessarily make them left-handed. Those who lack the gene are 50% likely to be either right or left-handed. Those who lack the gene pass the trait to their children through the conventions of standard genetics. This theory has never been proven, and the right-handed gene has not yet been located. Another group of researchers claims to have located a gene that shows and increased incidence of left-handedness. Possession of this gene also shows an increase in psychosis. A correlation does exist between being left-handed and developing mental illness.
On the other side of the coin is Dr. Stanley Coren. Dr. Coren’s studies seem to show that left-handedness is acquired as a fetus develops inside the womb and has nothing to do with genetics. He believes that a baby exposed to traumas during development show higher rates of left-handedness. Dr. Coren expresses that the brain damage during development that causes left-handedness also explains the increased rates of mental illness. He also asserts that the reason left-handers have left-handed children is due to the fact that the women in those families have histories of difficult pregnancies.
What we know for sure about handedness is that 90% of people are right-handed. Right-handed couples have right-handed children at the rate of 92%. A mixed righty/lefty couple has right-handed children at the rate of 80%. Left-handed couples have children who are 50% left-handed and 50% right-handed.
 Posted 5177 day ago
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