Two theoretical single-gene models have been proposed to explain the patterns of inheritance of handedness, by Marian Annett of the University of Leicester, and by Chris McManus of UCL. (2006) indicates that the heritability of handedness is roughly 24%. A large study of twins from 25,732 families by Medland et al.
For example, if both parents of a child are left-handed, there is a 26% chance of that child being left-handed. Handedness displays a complex inheritance pattern.
This finding is likely due to the small proportion of left-handers who have atypical brain organisation. When tasks investigating lateralisation are averaged across a group of left-handers, the overall effect is that left-handers show the same pattern of data as right-handers, but with a reduced asymmetry. Others have more ambiguous bilateral organisation, where both hemispheres do parts of typically lateralised functions. Some of those have reversed brain organisation, where the verbal processing takes place in the right-hemisphere and visuospatial processing is dominant to the left hemisphere. Only around 30% of left-handers are not left-hemisphere dominant for language. However, the majority of left-handers have been found to have left-hemisphere language dominance-just like right-handers. The theory depends on left-handed people having a reversed organisation. As the right hand is controlled by the left hemisphere (and the left hand is controlled by the right hemisphere) most people are, therefore right-handed. As speech is a very complex motor control task, the specialised fine motor areas controlling speech are most efficiently used to also control fine motor movement in the dominant hand. The theory suggests it is more efficient for the brain to divide major tasks between the hemispheres-thus most people may use the non-speaking (right) hemisphere for perception and gross motor skills. In most people, the left side of the brain controls speaking. One common handedness theory is the brain hemisphere division of labor. There are several theories of how handedness develops. More recently, the Flinders Handedness Survey (FLANDERS) has been developed. The longer Waterloo Handedness Questionnaire is not widely accessible. The Edinburgh Handedness Inventory has been used since 1971 but contains many dated questions and is hard to score. Handedness may be measured behaviourally (performance measures) or through questionnaires (preference measures). This cannot be learned and is highly associated with the person's childhood brain development. This is very uncommon in the population with less than 1% prevalence.
Left-handed people are also more prone to certain health problems. In many countries, left-handed people are or were required to write with their right hands. Most of the current research suggests that left-handedness has an epigenetic marker-a combination of genetics, biology and the environment.īecause the vast majority of the population is right-handed, many devices are designed for use by right-handed people, making their use by left-handed people more difficult. There are examples of true ambidexterity (equal preference of either hand), but it is rare-most people prefer using one hand for most purposes. Handedness is often defined by one's writing hand, as it is fairly common for people to prefer to do some tasks with each hand. And finally, cross-dominant (mixed-handed) people make up less than 1% of the population. Ambidextrious people make up 1% of the population. Left-handed people make up 8-9% of the population. Right-handedness is by far more common about 90% of the human population are right hand dominant. The other hand, comparatively often the weaker, less dextrous or simply less subjectively preferred, is called the non-dominant hand. In human biology, handedness is an individual's preferential use of one hand, known as the dominant hand, due to it being stronger, faster or better in dexterity. Left hands make up over 90% of the artwork, demonstrating the prevalence of right-handedness Stenciled hands at the Cueva de las Manos in Argentina.
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