What makes a person a lefty or a righty

If a particular version of this gene is inherited, the child may be more likely to be left-handed, depending on reinforcement and other environmental influences. Sex — slightly more boys than girls are left-handed.

This suggests to some researchers that the male hormone testosterone has an influence on right and left-handedness.

Fetal development — some researchers believe that handedness has more of an environmental influence than genetic. They propose that environmental factors in the womb including exposure to hormones may influence whether we favour the right or left hand later in life. Modelling — children learn to choose their right or left hand by copying parents and other significant caregivers.

Brain damage — a small percentage of researchers theorise that all human beings are meant to be right-handed, but some type of brain damage early in life causes left-handedness. For left-handers and parents of lefthanders, it is important to note there is no hard evidence to support this rather controversial theory. Adjustment — some people who are naturally right-handed become left-handed because of the need to adjust to injury.

The development of preferred handedness Very young children often use both hands equally. Researchers still looking for answers The brain has two hemispheres, the left and the right. Cross laterality explained Cross laterality is an ambidextrous mixture for example, being left handed but dominant in the right eye and foot. Problems for left-handed people Since 90 per cent of the population is right-handed, left-handed people do experience some practical problems, including: Western writing runs from left to right.

This is a natural inclination, not a sign of dyslexia, and will resolve given time, practice and encouragement. Implements such as scissors are designed for use with the right hand. Tools such as circular saws can be dangerous if operated with the left rather than the right hand. Some research has suggested that learning difficulties, epilepsy and autism are more common in left-handed people.

Individuals with the C gene will have a 50 percent chance of being right-handed and a 50 percent chance of being left-handed.

These theories of hand preference causation are intriguing because they can account for the fact that the side of hand preference of individuals with the C gene most left-handers and some right-handers can be influenced by external cultural and societal pressures, a phenomenon that researchers have documented. These theories can also explain the presence of right-handed children in families with left-handed parents and the presence of left-handed children in families with right-handed parents.

If the familial genetic pool contains C genes, then hand preference becomes amenable to chance influences, including the pressures of familial training and other environmental interventions that favor the use of one hand over the other.

The proposed genetic locus that determines hand preference contains an allele from each parent, and the various possible genetic combinations are DD individuals who are strongly right-handed, DC individuals who are also mostly right-handed, and CC individuals who are either right-handed or left-handed. These genetic combinations leave us with an overwhelming majority of human right-handers and a small, but persistently occurring, minority of left-handers.

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