*Scientist used to think that left-and right handedness was purely a genetic trait,but now they have doubts.Reason:In 20% of all sets of identical twins,one sibling is left-handed, and the is right handed.
*Some scientist think the hand hand you prefer is determined by whether you're a "right-brained" person or a"left brained" person.
*The right half of the brain controls the left side of the body,as well as spartial/musical/asthetic judgement and perception;the left half controls the right side of the body,plus communication skills.Lefties are generally right brained.
*Support for this theory:Most children begin demonstrating a prefenrence for one hand over the other at the same time their central nervous system is growing and maturing.This leads some scientist to believe the two processes are linked.
*According to another theory,before birth all babies are right handed which means that the left brain is dominant.But during a stressful or difficult birth,oxygen deficiency can cause the damage to the left side of the brain,making it weaker and enabling the right side to compete againts it for dominance.If the right side wins out,the baby will become left handed
*The theory also explain,researches claim,why twins,anychild born to a smoker,or children born to a mother more than 30 years old are more likely to be left handed:they are more prone to stressful births.Children of stressful births are also more likely to stammer and suffer dyslexia,traits are more common in lefties.
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