Most children have a preference for using one hand or the other by the age of about 18 months, and are definitely right or left-handed by about the age of three. However, a recent UK study of unborn babies found that handedness might develop in utero.
About nine out of 10 unborn babies preferred to suck their right rather than their left thumb, and this hand preference was borne out later in life. The brain has two hemispheres, the left and the right. Researchers into the brain once believed that handedness revealed which brain hemisphere was dominant.
While some people use one hand exclusively for all tasks, others tend to swap depending on the activity; for example, some people write with their left hand but open jars with their right. It was once believed that a right-handed person has general dominance on the right side of their body, which means their favoured foot, eye and ear are also on their right side. Many people may be right-handed but, for example, always take the first step with their left foot.
Cross laterality is an ambidextrous mixture for example, being left handed but dominant in the right eye and foot. This may cause coordination difficulties. However, some sports such as gymnastics benefit from the distribution of brain dominance.
Research into cross laterality is ongoing. Since 90 per cent of the population is right-handed, left-handed people do experience some practical problems, including:. This page has been produced in consultation with and approved by:. The abdominal muscles support the trunk, allow movement and hold organs in place by regulating internal abdominal pressure.
People who run regularly seem to be susceptible to Achilles tendonitis. Acromegaly is caused by an excess of growth hormone in adults, which causes the overgrowth of bones in the face, hands, feet and internal organs. Exercise can prevent age-related changes to muscles, bones and joints and can reverse these changes too. A person with amyloidosis produces aggregates of insoluble protein that cannot be eliminated from the body.
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The information and materials contained on this website are not intended to constitute a comprehensive guide concerning all aspects of the therapy, product or treatment described on the website. Researchers hope that figuring out handedness will help them better understand brain organization and the causes of conditions such as dyslexia, stuttering, autism and schizophrenia.
Such problems often coincide with abnormal lateralization, or left-right brain specialization. Many lefties have flipped lateralization, with the right side of the brain controlling speech and language instead of the left.
In July, British researchers reported they had pinpointed a gene linked with left-handedness and schizophrenia. McManus says the number of southpaws seems to have started waning between and He speculates that the trend may have something to do with England's Industrial Revolution, which occurred around that time and brought with it the rise of factory work on machines—designed for righties, of course. Already a subscriber? Sign in. Thanks for reading Scientific American.
Create your free account or Sign in to continue. Like PCSK6, the effect that these genes have on handedness depends on how many mutations the alleles undergo. Each gene has the potential for mutation—the more mutations a person has in any one direction toward right handedness or left handedness the more likely they are to use that hand as their dominant hand, or so the researchers speculate.
In mice, the disruption of PCSK6 resulted in serious abnormal positioning of organs in their bodies. One predominant hypothesis for this bias relates to another distinct human trait: language ability. Language ability is split between the different hemispheres of the brain, much like handedness, which suggests that handedness became compartmentalized along with language ability, For most, the parts of the brain that govern language are are present in the left-side of the brain—these people tend to be right-handed.
The few that have language skills focused in the right side of the brain tend to be left-handed.
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